Wikipedia talk:Manual of Style/Dates and numbers

RFC for units of the longest distances

What units should be used for distances between star systems and galaxies? These are measured in light years (ly) in popular news and educational media; professional astronomers use parsecs (pc). Articles currently use a variety of units (some only ly and some ly converted to km) but most commonly use ly converted to pc in infoboxes (often automatically from technical data). If conversion to SI units (like kilometers) is not required in certain contexts, this would be added as an explicit exception to MOS:CONVERSIONS. The maximum distance in the observable universe is under 100 billion light-years, and interplanetary distances (inside a star system) are a fraction of a light-year and are measured in astronomical units (AU or au). 01:40, 28 July 2024 (UTC)

Two formats are needed: an expanded format for use in article prose (especially on first mention), and a compact format for infoboxes, tables, and prose where the expanded format would be excessively long. The "unless this would be excessive given the context" rule from MOS:CONVERSIONS will still apply when the units are used several times in prose. First use of light-year/ly, parsec/pc, and rare meter prefixes (e.g. zettameter) must be linked to their articles, per MOS:UNITS. The chosen formats need to accommodate simple cases and complex expressions of precision (examples below).

The choices nominated for inclusion are:

• Light-year (ly) with SI prefixes (kly, Mly, Gly) and large number words (million, billion) in prose
  • 34.6 ± 0.3 million light-years (ly) [first mention in prose]
  • 34.6 ± 0.3 Mly [compact]
  • 408–548+90
    −49 ly [compact]
• Parsec (pc) with SI prefixes (kpc, Mpc, Gpc)
  • 765 ± 2 kiloparsecs (kpc) [first mention in prose]
  • 765 ± 2 kpc [compact]
  • 125-168.1+27.5
    −14.9 pc [compact]
• Kilometer (km) with scientific notation
  • 3.27×10¹⁴ km [compact, secondary in prose]
  • 3.273×10¹⁴ ± 2.8×10¹² km [compact, secondary prose]
  • 68.1+7.5
    −4.1×10¹⁴ km [compact, secondary in prose]
  • 3.27×10¹⁴ kilometres [primary expanded]
• Meter with SI prefixes (Ym, Zm, Em, Pm, Tm)
  • 68.1 zettameters (Zm) [first mention in prose]
  • 68.1 Zm [compact]
  • 68.1+7.5
    −4.1 Zm [compact]

You can of course advocate for as many or few options as you find appropriate, or assert multiple options are equally good, but previous discussion has assumed at most two units would be used because many editors find three to be excessive. Please specify your preferred order; "primary" units come first and other units are converted to (typically in parentheses in prose, sometimes on a new line or after semicolon in infoboxes).

01:40, 28 July 2024 (UTC)

Your preferred units

Please note your preferred units for both compact-in-infobox and expanded-in-prose if they are different.

• Light-years only. If there's a second unit, strong preference for kilometers. Astronomy infoboxes are already number-heavy; adding conversions makes them even more overwheming and unapproachable to the general public, which is a chronic problem in popularizing science. Light-years give nice, easy-to-understand small numbers for which we don't need exponential notation, avoiding overloading brains and having people mentally label everything from planets to galaxies as "incomprehensibly far" and more or less equally distant. It's easy to remember Alpha Centauri is about 4 ly away and the Milky Way is ~100,000 ly across and calibrate intuition from there. The speed of interstellar spacecraft (of which there are none) are sensibly measured in fractions of c, not km/s, and not parsecs per year (!?). If there is going to be a secondary unit, I strongly prefer kilometers, for consistency with all other articles and smaller measurements in infoboxes. Parsecs are too close to light-years and are only useful to specialists, who can easily do the conversion if they need to. I'm less opposed to conversion to km in prose because it feels less overwhelming, especially if it's only done sparingly, and it gives a sense of just how big a light-year is compared to everyday life. That said, it's not wrong to expect people to develop an intuition of how big a light-year is on their own or by reading light-year if they are new to the concept. -- Beland (talk) 01:44, 28 July 2024 (UTC)
• Parsecs or light years as primary, kilometres as secondary (converted) unit. I have no strong opinion regarding the use of pc or ly as primary unit, but figure that pc are to be more useful since they are preferred by specialists. I strongly favour the use of SI units with scientific notation as secondary unit, since it'll give normal (lay) readers a better sense of the dimensions involved – most people know what a kilometre is, and even those more accustomed to miles will know that they are of roughly the same scale. Using other SI prefixes such as zettametres would in theory comply even better with the SI, but few people know prefixes of such dimensions, so in practice it would be much less helpful than km with scientific notation. Gawaon (talk) 05:44, 28 July 2024 (UTC)
• Light-years first, parsecs second. We need to use light-years because that's what our readers understand, and parsecs because that's what our sources use. km is useless, both for intuitive understanding (a gigantic exponent gives no intuition other than gigantic distance), and for calculations (as relevant speeds are given in fractions of c). Em, Zm, Ym are even worse, these SI prefixes are way too obscure. Tercer (talk) 08:17, 28 July 2024 (UTC)
• Light-years only. Agree (mostly) with Beland. Lightyears give an understandable number for the general public such that distances to different stars can be compared (eg 4 light-years to Alpha Centauri vs 100,000 light-years for the width of the galaxy). km's at that scale are all are read as an equal "damn that's big!" and are totally unrelatable - the average reader simply does not think in terms of numbers that big. km clutters up the article with no payback. Parsecs are not known to the general public (professionals know how to convert and probably get their information from better sources than WP anyway).  Stepho  talk  08:47, 28 July 2024 (UTC)
• Light-years first, whatever unit is the primary unit used in the source second. We should be making it easy for our readers to understand, and not trying to shoehorn the content into some "official" style that will be more or less meaningless to many readers. I do support converting the primary unit used in the source to light-years, flipping the output as needed. - Donald Albury 17:45, 28 July 2024 (UTC)
• Light-years, because that's the unit used by Patrick Moore, one of the most prolific authors of popular astronomy books. If the source uses another unit, state that as well, using {{convert}} with |order=flip. For example, if the source says 123 parsecs, we would enter {{convert|123|pc|order=flip}} which emits 400 light-years (123 pc). --Redrose64 🌹 (talk) 18:08, 28 July 2024 (UTC)
• Parsecs, or if necessary pc+ly (pc first) using {{convert}}, for consistency with the professional literature. We need Wikipedia to be usable as a professional resource, not merely a dumbed-down only-for-the-public childrens' encyclopedia. —David Eppstein (talk) 18:34, 28 July 2024 (UTC)

  The guideline Wikipedia:Make technical articles understandable makes a useful distinction between what I would consider "dumbing down" - WP:OVERSIMPLIFY which says not to oversimplify or tell lies-to-children - and "writing one level down", which WP:ONEDOWN says is a good rule of thumb for technical subjects.

  In finding a middle ground between the overly technical and the oversimplified, §Avoid overly technical language specifically advises: "If no precision is lost, use common terms instead of technical terms. Substitute technical terms with common terms where they are completely equivalent." Whether that advice should apply in this situation is a matter of opinion, but I think it's important to remember that "making accessible" and "dumbing down" are not always the same thing. -- Beland (talk) 15:54, 29 July 2024 (UTC)

  Making accessible should also mean, making accessible for professionals to read and to edit. "The widest possible general audience" should include professionals, not just non-professionals. Gratuitously avoiding the preferred unit of professionals makes our articles less usable to and less editable by them, for no good reason. It sends the message that their participation is not welcome here, the opposite of what we want. —David Eppstein (talk) 01:49, 30 July 2024 (UTC)

  The discussion in the previous thread has several examples of peer-reviewed astronomy papers that use light-years, even though it's not the majority, and the unit is well-known in the popular press, which professional astronomers are also exposed to. Light-years should be perfectly accessible to professional astronomers and those familiar with the peer-reviewed literature, and no doubt already occasionally use the conversion factor to compare figures from different sources.

  I was also pondering whether or not it would be good to also have parsecs to attract more professionals to use Wikipedia articles for quick reference, and possibly fix things while they are here. This past week I went through and fixed the densities and surface gravities of a lot of exoplanets; a few seemed completely wrong because someone had confused g/cm³ with kg/m³ or missed undoing a logarithm or just pulled data from a contradictory source without leaving a citation. Those sorts of things I would expect a professional to occasionally spot.

  I think it would be good to get actual data about whether or not this makes a certain community feel unwelcome, rather than go on the guesses of non-astronomers about other people's emotional reactions. Does not using US units in science articles make Americans feel unwelcome? This American certainly does not, so I'm a bit skeptical of this idea. I might feel differently if someone did it intentionally to spite Americans rather than for good reasons, like reducing clutter for a global audience and the fact that STEM fields tend to use metric and Americans are an inconvenient minority on the planet in this aspect. I took some astronomy and planetary science classes while I was an undergrad at MIT, but I'm definitely not a career astronomer. Is anyone else here a professional astronomer or know someone who is and is uninvolved in this discussion so far? -- Beland (talk) 03:29, 30 July 2024 (UTC)

  (See Parejkoj's reply, below, for one answer.) -- Beland (talk) 18:34, 1 August 2024 (UTC)

• Light-years as primary unit, as the most familiar and understandable way of expressing interstellar distances. Parsecs as secondary unit, as the unit most often used by professional astronomers. Sources always use one or both of light-years and parsecs. While I prefer the status quo of using both I would also be okay with only light-years; compact tables like the list of nearest stars should use only light-years. Using large numbers of kilometers is not supported by common usage, and it seems clear that this being more understandable than light-years is a minority position. SevenSpheres (talk) 18:38, 28 July 2024 (UTC)
• Light-years as primary unit (and perhaps the only unit) as the mostly widely understood unit. I don't like the idea of using parsecs. The point of providing multiple units is to allow the reader to understand the number if they are unfamiliar with the primary unit. I can't imagine that there's anyone who knows what a parsec is but doesn't know what a light-year is. Parsecs are used only by professional astronomers, who certainly know what a light-year is and can easily convert between light-years and parsecs. Furthermore, it seems unlikely to me that a professional astronomer would be doing research using Wikipedia rather than more professional resources. Well-respected popular science magazines like Astronomy and Scientific American use light-years. Weak preference for km as a secondary unit if a secondary unit is necessary, although the huge numbers involved in the conversion to km will probably be hard to understand for a significant number of our readers. CodeTalker (talk) 19:05, 28 July 2024 (UTC)

  Well, if edited with that attitude, it is unlikely that our astronomy articles will be usable by professional astronomers. But in other areas of science, Wikipedia is usable, useful, and used by professional researchers, not so much as a source for data but as a good starting point for literature reviews and starting material for understanding topics with which they may not already be familiar. —David Eppstein (talk) 20:02, 28 July 2024 (UTC)

  I certainly know chemists who use Wikipedia to look up reference data on certain molecules sometimes, but when doing so occasionally spot errors. We generally don't convert those data to secondary units in chem infoboxes (though I do see some Fahrenheit). It seems the benefits of using a single set of units - which we're lucky enough to also be those used in industrial and academic chemistry - outweigh the convenience for Americans who might be thinking or calculating in US units. It seems a bit much to claim that using light-years and not parsecs would make Wikipedia articles unusable for astronomers; how hard is it to divide by 3.26? -- Beland (talk) 05:24, 29 July 2024 (UTC)

  @CodeTalker: The "huge numbers involved in the conversion to km" are one reason why such a conversion is helpful. An astronomer does not need reminding of that vastness, and uses parsecs for convenience, but the mindboggling vastness of space is lost when we use correspondingly vast units. The mindbogglingly large numbers resulting from a conversion to km (or mi) is one way of conveying the vastness to a lay reader. Dondervogel 2 (talk) 19:12, 1 August 2024 (UTC)

  My opinion is that "conveying vastness" should not be a goal. The goal should be writing in a way that helps the reader to understand, not to awe them with wonder. I think few readers who are not already mathematically inclined will take anything away from numbers like 10²⁰ km or 10²⁵ km, except that they're both "very big", without any understanding of what they really mean or the difference between them. CodeTalker (talk) 19:36, 1 August 2024 (UTC)

  If it is not Wikipedia's goal to convey how far away the stars are, then I too see little point in converting to km (or Zm). There we can agree.

  But in my view a good encylopaedia should strive to convey precisely that. It seems this is where we differ. Dondervogel 2 (talk) 20:10, 1 August 2024 (UTC)

  Of course our goal is to convey how far away the stars are. I don't see how you can read my response to mean that we should not. But it should be done in a way that is understandable to readers, not to deliberately use inappropriate units so that we can impress the reader with big numbers. CodeTalker (talk) 20:16, 1 August 2024 (UTC)

  Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space. Listen... – Douglas Adams, "Fit the Second", The Hitchhiker's Guide to the Galaxy.

  The point is that we cannot conceive very large numbers, so there's no point in choosing one unit over another unless you are comparing one distance with another, in which case you can judge that this object is ten times as far away as that object, when measured using the same units. --Redrose64 🌹 (talk) 21:01, 1 August 2024 (UTC)

  Your precise words were "conveying vastness" should not be a goal. I interpreted that as meaning Wikipedia should not try to convey the vastness of space. I see no other reasonable interpretation. If not that, what did you mean instead? Dondervogel 2 (talk) 22:35, 1 August 2024 (UTC)

  Not to put words in anyone's mouth, but I think the idea is that light years give small numbers that can be readily compared to easily comprehend relative distance. Distances in light years convey the mathematical information about how far away the stars are, but do not convey a realistic sense of sheer vastness unless one already has an intuition for how vast a light-year is. As compared to kilometers, which can (for those who understand scientific notation and who stop to think for a moment) convey an intuitive sense of how far away stars are in absolute terms, for example by making it easy to see how long it would take to drive there at 100 km/h or how long it would take Voyager 2 to get there at 15 km/s. -- Beland (talk) 03:43, 2 August 2024 (UTC)

  Yep. The distances need to be presented in light-years (or parsecs), to provide relative distances and in kilometres (or metres) to convey the vastness. Very well put. Dondervogel 2 (talk) 06:37, 2 August 2024 (UTC)

  The main sticking point here seems to be over if it is within our purpose to do so (re: km conversion).

  Personally, I would say it is not. ... for example by making it easy to see how long it would take to drive there at 100 km/h or how long it would take Voyager 2 to get there at 15 km/s. Including conversions solely for this purpose feels uncomfortably close to WP:INDISCRIMINATE to me. Unit conversions are included for reasons of practicality, not for conveying "vastness" or other arbitrary properties.

  There are, of course, other arguments for include km conversions that others have laid out, but I feel that this specific line of reasoning is a weak one. ArkHyena (talk) 08:05, 2 August 2024 (UTC)

  Conveying vastness essentially means providing a comparison with a familiar unit. Thus providing distances in, say, kilometres enables readers to compare the distance to a measure they use frequently, and providing them in a large unit such as light years enables readers to more easily compare the relative distance for different stars. isaacl (talk) 13:35, 2 August 2024 (UTC)

  My stance that such a reason alone is not sufficient still stands. I fail to see how SI conversions would enable a reader to more easily compare the relative distance for different stars, because that is, in part, why we use lyr/pc in the first place. A star 50 lyr away being twice as distant as a star 25 lyr away is perfectly understandable to the reader. On the topic of vastness, we don't provide the masses of planets in kg just to convey to the reader how massive they are with impressively large numbers, we include them because

  • Kg are occasionally, if not frequently used by astronomers when dealing with the masses of celestial objects, including planetary ones
  • There are relevant attributes that rely on their masses being given in kg, such as planetary densities, planetary compositions, or the masses of a planet's internal layers

  If we are to include SI conversions for lyr/pc, we ought to do so for similarly practical reasons. ArkHyena (talk) 19:50, 2 August 2024 (UTC)

• My previous position was parsec or light-year as primary unit, converted to SI, but I now favour parsec as primary unit, converted to SI. I will explain the rationale behind the shift in a follow-up post, but my thoughts remain in a state of flux and the popularity of the light-year makes me consider the need for a 3-way conversion in some situations. I will be back. Dondervogel 2 (talk) 21:14, 28 July 2024 (UTC)

  … and my considered preference is Parsec as primary unit, converted to an SI unit. In prose, convert also to light-years, thousands of light-years, millions of light-years, billions of light-years (avoiding the abbreviations 'ly', 'kly', 'Mly', 'Gly'), as appropriate.

  My preferred SI unit would be Pm, Em, Zm or Ym, linked on first use to petametre, exametre, zettametre, yottametre. I can see the benefit of relating to the kilometre (km), so I would not object to that option, although I find the exponential notation cumbersome.

  As mentioned in my previous post, I no longer favour the use of light-year as a primary unit. I was already uneasy about “megalight-year” and similar but was unsure why. When I dug a little deeper I discovered the IAU style manual, which lists SI units and non-SI units recognised for use in astronomy. The units recognised by the IAU are the metre (symbol m), the astronomical unit (symbol au = 0.149 60 Tm) and the parsec (symbol pc = 30.857 Pm). In other words, the IAU does not recognise the light-year for use in astronomy. And if the IAU does not recognise the unit, we should not use it, right? No, not quite. Many Wikipedia readers will know a light-year is the distance light travels in a year, and this familiarity makes it relevant, hence the proposed additional conversion (in prose) to light-years, but avoiding the abbreviations ly, Mly, etc., which I find unhelpful.

  The conversion to SI provides a scale (whether the metre or kilometre) that all readers are familiar with and conveys the vastness of space in a way that parsec (or light-year) on their own do not achieve (Readers who understand the meaning of ‘light-year’ as the distance travelled by light in a year do not necessarily have a grasp of how fast light travels; only yesterday I was asked “what travels faster, light or sound?”)

  Examples

  • Sirius B is 2.670 pc (82.4 Pm; 8.71 light-years) from the Sun.
  • The Whirlpool Galaxy is 7.220 Mpc (223 Zm; 23.5 million light-years) from the Sun and 23.58 kpc (0.728 Zm; 76,900 light-years) in diameter.

  The use of 0.728 Zm in preference to 728 Em avoids an unnecessary conversion between Zm and Em in the 2nd example. The SI values could be replaced with exponential notation if that is preferred. I find it cumbersome but that is a personal preference. Dondervogel 2 (talk) 13:57, 29 July 2024 (UTC)

  Finally someone who would agree with me in the discussion on prefixes I started. Avenues2009 (talk) 21:37, 30 July 2024 (UTC)

  I can see the benefit of SI prefixes in astronomy and nuclear physics, because the prefixes obviate the need for cumbersome exponential notation. Where we differ is your statement it would be much more consistent and straightforward if all Wikipedia articles used the full range of metric prefixes, which differs from my position. In 99.9 % of our articles it is preferable to use a scale between "millionths of a millimetre" and "millions of kilometres", as appropriate. Dondervogel 2 (talk) 09:11, 31 July 2024 (UTC)

• Light-years as primary unit, parsecs as secondary unit, as lyr are indisputably the primary unit used to convey interstellar distances or larger. I don't see why distances measured by lyr/pc should be converted as such distances are well into the region where scales conveyed by kilometers are, at best, impractical and unintuitive to most. This is evidenced by numerous science communication outlets—including NASA itself—excluding SI (or US customary) conversions for interstellar distances (some examples: [1] [2] [3] [4]). It is clear that the overwhelming majority of science communication, nevermind technical introductory sources such as astronomy textbooks, deems such conversions as largely unnecessary, and I fail to see why we should be any different. ArkHyena (talk) 02:52, 31 July 2024 (UTC)

  None of the web pages you linked use parsecs, either. -- Beland (talk) 03:17, 31 July 2024 (UTC)

  Yes, but this is balanced by the fact that academic sources overwhelmingly use pc over lyr. Popular sources use lyr, academia uses pc; per this, we should use both, with the less technical lyr being our primary unit. ArkHyena (talk) 03:19, 31 July 2024 (UTC)

  Interestingly, our dab page lyr doesn't mention light-years. --Redrose64 🌹 (talk) 19:59, 31 July 2024 (UTC)

  Should be fixed now, thanks for the heads up :) ArkHyena (talk) 20:04, 31 July 2024 (UTC)

  Our article light-year also doesn't mention "lyr", a contraction which I had never come across until your post of 02:52, 31 July 2024 (UTC) - everybody else in this section, when abbreviating, has used "ly". I hope that "lyr" is not something that you made up. --Redrose64 🌹 (talk) 07:13, 1 August 2024 (UTC)

  I suppose it's a mistake. Gawaon (talk) 07:33, 1 August 2024 (UTC)

  Both "ly" and "lyr" are legitimate abbreviations of "light-year". I have seen "lyr" in reliable sources (e.g., Mutel et al 1981; Chen & Chen 2016). It should be mentioned in Light-year as a legitimate alternative to "ly". Dondervogel 2 (talk) 08:05, 1 August 2024 (UTC)

  I have added "lyr", "klyr" and "Glyr" to Light-year, citing RS. Dondervogel 2 (talk) 08:17, 1 August 2024 (UTC)

• Light years as primary, small preference for conversion to parsecs in extended prose. Professional astronomer here (there's about a half dozen that I know of that semi-regularly edit Wikipedia): parsec is really useful because the relationship between arcsec, au, and pc (and the conversion factor of 206,265) allows really easy conversion between measured angular sizes, proper motions, distances, etc. in one's head. But that's not something that most people will ever have to care about, so there's not a strong reason to use pc on Wikipedia, except that that is the value that most primary sources report. I like the suggestion above to use `order=flip` in the converter, since that helps make it clear where the value came from: we have a terrible problem of un- and poorly-sourced numbers in astronomy articles.
  Metric prefixes for meter are right out: most astronomical scales are well beyond what any typical reader would be familiar with; I work computing, and still have to remind myself what the exponent for peta is. Prefixes above giga would be completely unfamiliar to most readers.
  To the question of whether astronomers are, or should be, using Wikipedia as a data source: I mostly hope that they do not. We have our own curated sources for data values (e.g. NED, SIMBAD, or the SDSS value added catalogs), and it's almost always not as simple as just grabbing the "top" value from a catalog. This often happens on Wikipedia, and results in long arguments by non-experts about e.g. which star is biggest. I've tried at various points to get colleagues to edit wiki pages when they notice something incorrect without much success; you don't get tenure or grant funding editing wiki! We're not going to turn Wikipedia into a preferred source of numerical values without essentially re-creating the work that went into something like SIMBAD, and that took *significant* funding and buy-in from institutions. Trying to re-create that work without experts onboard is not worth our time. - Parejkoj (talk) 03:58, 31 July 2024 (UTC)
• Light years as primary. I would include a conversion to parsecs (using order=flip if it helps). Light-years are widely recognised by the lay reader, which will be most of our audiences. Parsecs are more likely to be found in sources (so including them helps with verification) and will be needed if we aspire to have an audience of professionals. I would not strongly object to a third conversion to kilometres where space allows, but I would strongly object to the use of obscure metric prefixes that would not be readily understood even by professional astronomers or other professional scientists. Shoot, even names of large numbers are more understandable to more people (even if we restrict ourselves to professionals) than most of the larger metric prefixes. At least you can work out how big a quintillion is from its name. You can't do that with exa-, zetta- or yotta-. Kahastok talk 21:40, 2 August 2024 (UTC)

  I feel it's worth adding something on the kilometres point. My view is that conversions from light years to kilometres are unnecessary in general. Such conversions are almost never found in other sources on the topic. And that's because systematically converting interstellar distance to kilometres is as useful as systematically converting the lengths of running races into light-years. In general, I believe that light-years are sufficiently well-known that, per my point below, most readers will understand them. However, I do not strongly object. I do see some small amount of value in helping readers quantify some of these very large distances in niche circumstances, and I don't see a huge harm in using them occasionally - in infoboxes but not in prose, for example. Of course, no such value arises from units using obscure SI prefixes to create things like exametres and zettametres, as these are less likely to be understood than the units they're supposed to be trying to explain. Kahastok talk 17:14, 3 August 2024 (UTC)

• Lightyears first, with parsecs (second choice: parsecs + lightyears). Lightyears first, for our general readers. Parsecs second, for those more familar with astronomy at that scale, readers and editors both, and for the sake of our reputation. Not kilometres, for several reasons; my big two are that few have the skill of comparing values in exponent notation at a glance, without having to separately scale left and right portions, and that any comparison to terrestrial dimensions or speeds tells us only that each sidereal distance is vastly greater and would take inordinate time to cross at any ordinary travel speed, but nothing about this or that particular sidereal distance – or to put it another way, kilometre sidereal distances are good for the sort of fantasy math that we might try once or twice in a lifetime but not for regular use across the 'pedia. NebY (talk) 17:01, 21 August 2024 (UTC)

Summing up

This RFC has had its 30-day run, so it seems time to wrap it up. Trying to boil the comments above down to editor preferences, my ordered tally is:

• Ly, none or km
• Pc or ly, km
• Ly, pc
• Ly, none
• Ly, source
• Ly, source
• Pc, none or ly
• Ly, pc
• Ly, none or km
• Pc, Pm or km
• Ly, pc
• Ly, pc in prose
• Ly, pc
• Ly, pc

If I'm counting correctly (feel free to double-check me), out of 14 participants, that's:

• Primary: 11 ly, 1 pc or ly, 2 pc
• Secondary: 5 pc, 2 none or km, 1 km, 1 none (but pc in prose), 2 source, 1 none or ly, 1 Pm or km
• Tertiary: one non-objection to km, some objections in previous discussion

It seems there's a strong preference (79%) for light-year as primary unit, 86% if you count the vote for parsec or light-year.

For the secondary unit, taking the greatest number of supporters for each option (given the "or" votes), there are at most: 5 pc, 4 km, 4 none, 2 source, and 1 Pm. If we add in 3 votes from people who wanted parsec to be the primary unit, that's a solid 8 supporters for parsec, which is 57%, plus the preference for parsec in prose.

So, any objection to closing this RFC with light-year winning for primary unit and parsec for secondary unit? My proposed sub-bullet-point to add to the "Generally, conversions...except:" bullet point in MOS:CONVERSIONS would be the following. -- Beland (talk) 05:23, 6 September 2024 (UTC)

---

• For distances between star systems and galaxies, use "light-years" or "ly" as primary units, with a conversion to "parsecs" or "pc". Link the units on first mention and do not convert to SI units. For larger quantities, use large number words in prose (million or billion but not thousand) and metric prefixes (kly, Mly, Gly, kpc, Mpc, Gpc) in compact contexts. Examples:
  • First mention in prose: 34.6 ± 2.3 million light-years (10.6 ± 0.705 Mpc)
    • Wikitext: {{convert|34.6|±|2.3|e6ly|Mpc|sigfig=3|lk=on}}
  • Infobox or table: 2.50 Mly (765 kpc)
    • Wikitext: {{cvt|765|kpc|Mly|order=flip|sigfig=3|lk=on}} (use "order=flip" when source uses parsecs)

---

I think it's a fair summary of the outcome. But since we generally don't give commands, I'd suggest rewording the first two sentences to something like: "For distances between star systems and galaxies, "light-years" or "ly" should be used as primary units, with a conversion to "parsecs" or "pc", but no conversion to SI units. The units should be linked on first mention." Gawaon (talk) 08:24, 6 September 2024 (UTC)

Added to the MOS with your tweaks. -- Beland (talk) 17:26, 6 September 2024 (UTC)

Conversion of non-SI metric units

One part of MOS:CONVERSIONS says "conversions to and from metric units and US or imperial units should be provided". Another part says for units "not part of the SI or US customary systems (e.g. zolotnik), supply a parenthetical conversion into at least SI units". Should the latter part say "metric" or "modern metric" instead of "SI"? I may have been the one to put that in and merely chose the wrong words. I ask now because I came across jansky, which is a non-SI metric unit. It seems a bit silly to convert janskys to 10⁻²⁶ W⋅m⁻²⋅Hz⁻¹, which is apparently more strictly SI.

By "metric units" I assume it's clear we mean anything that's a named combination of SI units or can be related to them with factors of 10, which also includes the liter, hectare, and metric ton. Those three I assume we clearly don't want to convert, but to the degree that they are no longer used, it does seem like we'd want to avoid CGS and MTS units where there are drop-in SI equivalents, like erg or dyne or sthène? -- Beland (talk) 01:18, 30 July 2024 (UTC)

It's a bit tricky since "metric" would be very broad, while "modern metric" and SI seem to be largely treated as synonymous. (Metric system say "The International System of Units is the modern metric system"; similarly, International System of Units calls it "the modern form of the metric system".) Units officially accepted for use with the SI should be fine in general (though I'd still like to see the astronomical unit converted to km, but maybe others will disagree). For others, such as the jansky, it could be decided on a case-by-case basis – that one seems reasonable enough. I think rather than changing the text of that section, adding a note on other acceptable units might be a better solution – to be extended, if the need arises, after a short discussion on this page, or through WP:EDITCON. Gawaon (talk) 06:37, 30 July 2024 (UTC)

I don't think that a "metric unit" is necessarily related to an SI unit by an integer power of 10. The article List of metric units includes multiple examples that do not satisfy this criterion. Examples include the CGS-ESU electromagnetic units statcoulomb and statmho. Are these not metric units? Dondervogel 2 (talk) 07:36, 30 July 2024 (UTC)

CGS is obsolete. I assume it is the reason Beland mentioned "modern metric". Tercer (talk) 08:00, 30 July 2024 (UTC)

Yes that's why I was leaning toward "modern metric", though it's interesting to find out about non-base-10 metric units, so, well spotted!

It does seem like a specific list of exceptions to "convert to SI" is needed for clarity, especially since upon further research there are some units that meet my description that are so obscure I'd probably want to convert anyway. Maybe "metric" in the first sentence should actually be replaced by "SI"?

AU and eV have come up at Wikipedia:WikiProject Astronomy/Manual of Style. I was expecting to have a separate discussion about AU after we finalize a decision for light-years. For electronvolt and dalton, it seems like they are actually too small and fiddly, and are actually well-suited to the domains in which they are used, without conversions that would require scientific notation. If no one objects, I think it would make sense to say units officially accepted for use with the SI (except possibly for AU) don't need to be converted.

List of metric units was very helpful to look through for possible exceptions to the "otherwise convert to SI" rule. I tried to find the ones that would be awkward to convert into SI, either because the combo unit is very complicated, or the non-SI name is very common.

• Solar flux unit is complicated but doesn't look like it's used outside of articles about units.
• Rad (radiation unit) looks like it could be replaced in our articles with Gray (unit)
• Rutherford (unit) could perhaps be replaced with MBq
• M for molar concentration seems like a good candidate for leaving unconverted, due to common use.
• Rayleigh (unit) is complicated, but only used in a handful of articles; should probably be discussed.
• Currently, English Wikipedia articles on some planets have atmospheric pressure given in bar, atm, and Pa. Since 1 bar is exactly 100 kPa, that seems like overkill, and a good topic for the astronomy MOS. Measuring in standard atmospheres is nice because it's an intuitive comparison to Earth, though I guess given that the other scales are calibrated with 1 or 100 at Earth standard, maybe only one of these scales is actually necessary? I don't have a good sense of how well people in metric-using countries know bar and Pa, and if one would be better to use over the other or if they are both fine and could be used based on the field or article history or whatnot. Here in the US, the weather is in inHg, my bike tires are in psi, and I have no intuitive sense of how they relate to each other and vague memories of bar and torr from high school chemistry class. (Hlep!) -- Beland (talk) 08:42, 30 July 2024 (UTC)

The electronvolt and dalton are among the units officially accepted for use with the SI, so I think they should be fine to use without conversion. Molar as mol/L seems fine to me, since the mol is an official and the litre an accepted unit. As for rayleigh, I don't know – there doesn't seem to be any other common unit of photon flux, so it probably needs to be kept? Pressure should preferably be given in or converted to Pa, since that's the standard. Gawaon (talk) 09:18, 30 July 2024 (UTC)

Having lived in several countries that use SI, the kilopascal is the common and only unit for pressure in tires in Southern Africa, Australia and New Zealand. The hectopascal is used worldwide for atmospheric pressure (Canada uses kPa), the USA uses inches of mercury for surface pressure and millibars for upper air pressure. The bar and millibar are deprecated and not SI. What they are trying to do in the MOS is have SI primary for every country except the USA, Britain is a mix. Avi8tor (talk) 10:48, 30 July 2024 (UTC)

Here in Spain bar (and milibar) is used for pressure. In informal speech it is used interchangeably with atm. Pascal only exists in textbooks. Tercer (talk) 13:13, 30 July 2024 (UTC)

I was surprised to see erg (as sole unit) and erg/s (with a conversion to W) in Proxima Centauri, one of the examples in the discussion above. Is that common among astronomers?

Some use hectopascals (hPa) rather than mbar for terrestrial weather, as the values are identical, but in science ant technology generally it's Pa, kPa and Mpa with no glimpse of hPa. For inHg/psi, you probably see barometers go up to about 30 inHg and know standard atmospheric pressure's about 14.7 psi, so 2:1 is good enough for an intuitive relationship? NebY (talk) 17:54, 30 July 2024 (UTC)

Weather for pilots is in hPa worldwide because older altimeters are calibrated to millibars and nothing needs changing. Most airplanes now have a switch to change the display from inHg to hPa depending on where you are on the planet. Avi8tor (talk) 08:59, 31 July 2024 (UTC)

My point is not to develop an intuition about US pressure units, but to point out that for the vast majority of Americans that doesn't exist. -- Beland (talk) 19:20, 31 July 2024 (UTC)

Part of the problem here is that previous discussions have broadly used "SI" as a shorthand for the conventional systems of units used in most of the world outside the US and UK. It was never intended that we strictly use the SI interpretation of the metric system purely for its own sake, regardless of what the rest of the world uses. The people writing this probably weren't thinking of units used by scientists at all. They were thinking of things like Scandinavian miles, pennyweights and chains.

My rule of thumb for scientific articles would be to ask whether the reader (judged e.g. according to WP:ONEDOWN) is likely to be familiar with the unit. If so, no conversion is needed, just link it. If not, then you should convert to a unit that they will be familiar with. Kahastok talk 15:14, 3 August 2024 (UTC)

Sure, which is why a conversion into kilometres (with scientific notation) seems like a good idea. Gawaon (talk) 15:40, 3 August 2024 (UTC)

Depends what you're converting. If you're starting from something in Scandinavian miles, sure. If the starting value is in angstroms, I'd suggest metres or nanometres instead. Kahastok talk 16:56, 3 August 2024 (UTC)

Hehe, sure! Gawaon (talk) 17:37, 3 August 2024 (UTC)

Not all non-SI metric units can easily be converted to SI. For example, in the CGS system, the units of time and of temperature are the second and kelvin respectively, and no conversion is necessary. For some other units, there is a simple conversion by multiplication: the CGS units of mass and of length are the gram and centimetre respectively, and conversion of these to kilograms and metres involves multiplication factors of 0.001 or 0.01 respectively. But anything involving electricity or magnetism is fraught with danger: there are at least two CGS units of electric current, the abampere and statampere, one of which has the speed of light as a term; and one abampere (CGS) corresponds to, but is not equal to, 10 amperes (SI). --Redrose64 🌹 (talk) 15:50, 3 August 2024 (UTC)

All the more reason to always convert them to SI, lest the reader not know what we are talking about. This is a rather abstract concern, though, I have never met anyone that actually wanted to use the electrostatic/electromagnetic CGS units. Tercer (talk) 16:03, 3 August 2024 (UTC)

Draft treatment

Thanks, everyone, for the help in collecting observations about which units are in use around the world. The situation is complicated and I'm not sure what the best solution is for readers that would also satisfy the most editors here. To keep making progress, I've drafted some language, taking Gawaon's suggestion of explicitly listing the units we're talking about. In the process of doing this, I started to realize the great degree to which "core" metric units the general public uses are different than the "core" metric units defined by SI and whatnot, and that affects what level of explanation or linking is needed. That results in somewhat longer lists. Please take my draft only as a starting point for discussion; I don't actually have strong feelings about how these units should be treated and for some of them I just guessed or made an arbitrary choice.

The current text says:

• For units of measure that are obsolete, obscure outside of a particular specialty or geography (e.g. furlong), or not part of the SI or US customary systems... supply a parenthetical conversion into at least SI units

We could change "SI" to "metric" in both places and add list sub-items to clarify:

---

(version 1, edited based on below comments)

• Metric units should be commonly known, and commonly-known units approved for use with SI can be used without conversion in science-related articles or as a conversion target in other articles: meter (m), gram (g), second (s), ampere (A), liter (L), Pascal (Pa), hertz (Hz), degrees Celsius (°C), minute (min), hour (h), day (d), degree (of angle, °), volt (V), watt (W)
• Metric prefixes used should be commonly known, namely "pico" thru "tera", preferably in commonly-used combinations (e.g. 2,000 kilometers not 2 megameters).
• Metric units commonly used in certain fields but less familiar to the general public can be used without conversion in science-related articles or as a conversion target in other articles, as long as the unit name, abbreviation, or symbol is linked on the first instance and the property being measured is clear from context (e.g. that K is for a temperature): kelvin (K), mole (mol), candela (cd), hectare (ha), metric ton (t), joule (J), coulomb (C), radian (rad), steradian (sr), decibel (dB), arcminute (′), arcsecond (″), molar concentration (M), electronvolt (eV), dalton (Da), neper (Np), jansky (jy), gray (Gy), becquerel (Bq), sievert (Sv) tesla (T), farad (F), ohm (Ω), lumen (lm), lux (lx), siemens (unit) (S), henry (unit) (H)
• Obscure metric units should be linked and defined in basic SI units on first use: rayleigh (R), katal (kat), weber (Wb)
• Metric units other than those listed (e.g. in the CGS or MTS systems) should either be replaced with listed units (e.g. joules instead of ergs), or they should be treated as obscure units in the same way as furlongs.
• Some quantities expressed in listed metric units should also be converted into more intuitive field-specific units; see Wikipedia:WikiProject Astronomy/Manual of Style#Units
• (Light-year and parsec and astronomical unit will need to be added depending on the outcome of the RFC.)

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Later we would either add light-year and astronomical unit or link to Wikipedia:WikiProject Astronomy/Manual of Style, with the specific content depending on the outcome of the RFC. "Pico" thru "tera" are in everyday use according to Metric system, though that may be pushing the boundary of what Americans can cope with in STEM articles where there are no conversions to US units.

-- Beland (talk) 09:10, 14 August 2024 (UTC)

I would recommend using the pipe trick to remove (unit), e.g., [[mole (unit)|]] rendering as mole rather than [[mole (unit)]] rendering as mole (unit). -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 09:56, 14 August 2024 (UTC)

Sure, I wasn't trying to be tidy on the first pass. I just tweaked the draft to pipe as appropriate, not link where linking is not recommended, and show the symbol for each. I kind of grouped the units by topic and frequency and kind of just dropped them in as I came across them. Maybe alphabetical would work better instead? -- Beland (talk) 16:43, 14 August 2024 (UTC)

I needed some extra coffee, so can I check I understand the principles?

• Some common/familiar SI units and units approved for use with SI can be used without being linked.
• Less familar metric units should be linked on first use.
• Obscure metric units should be defined in base SI units on first use.
• Only familiar metric prefixes should be used, preferably in commonly-used combinations.
• Re conversion, effectively insert thus into the current text or rephrase to this effect: For units of measure that are obsolete, obscure outside of a particular specialty or geography (e.g. furlong), or not part of the SI (or units approved for use with SI) or US customary systems... supply a parenthetical conversion into at least SI units.

Are those the key points, in outline, or have I missed some? — Preceding unsigned comment added by NebY (talk • contribs) 7:13, 14 August 2024 (UTC)

Yes, except on the last item, change "SI" to "metric". -- Beland (talk) 16:20, 14 August 2024 (UTC)

Ah, that would be rather different. Do you mean this? For units of measure that are obsolete, obscure outside of a particular specialty or geography (e.g. furlong), or not metric or US customary units ... supply a parenthetical conversion into at least metric units. NebY (talk) 18:26, 14 August 2024 (UTC)

I should add now, because I might seem to be trying to entrap you, that this would not be wise.

Some units in three variants of the metric system

Quantity	SITooltip International System of Units/MKSTooltip Metre–kilogram–second system of units	CGSTooltip Centimetre–gram–second system of units	MTSTooltip Metre–tonne–second system of units
acceleration (a)	m/s2	gal (Gal)	m/s2
force (F)	newton (N)	dyne (dyn)	sthene (sn)
pressure (P or p)	pascal (Pa)	barye (Ba)	pièze (pz)
energy (E, Q, W)	joule (J)	erg (erg)	kilojoule (kJ)
power (P)	watt (W)	erg/s (erg/s)	kilowatt (kW)
viscosity (μ)	Pa⋅s	poise (P)	pz⋅s

The "metric system", unless specified as SI plus units approved for use with SI, comprises several different coherent variants and a number of, ahem, incoherent units too. It would be unacceptable to provide conversions into most of them. This table, copied from Metric system#Development of various metric systems, shows some. There are also calories, statcoulombs, abamperes (biots), the gauss, maxwells, apostilbs (blondels), skots, brils, stères, and variants on the variants – ampere-turn, international volt, millimetre of mercury (mmHg), metre head (mH₂O), metric horsepower, daraf, debye, demal (a measure of conductivity - our redirect is unhelpful), Einstein (unit) and on, and on. We mustn't go there. The SI units and the units approved for use with SI are the only metric targets we need or want, and have the virtue of being comprehensively documented in reliable sources, fully supported by {{Convert}}, and adopted by many countries and many standards organisations even in places that haven't fully metricated or metrified – NIST, ASME, ANSI and more.

If I've misunderstood you and this is all a straw man - phew! But let's be careful with this. NebY (talk) 20:10, 14 August 2024 (UTC)

You are exactly right; that was what I intended to convey, and I think I failed to do that clearly. Presumably for any units not explicitly listed, we want articles to either not use them or convert them into one of the units listed. I will add another bullet point to make that explicit. Tweaks and further discussion welcome. -- Beland (talk) 22:16, 14 August 2024 (UTC)

Oh, and yes, that was the new wording I intended. -- Beland (talk) 22:18, 14 August 2024 (UTC)

That sentence isn't right yet, or your first bullet isn't. The sentence would require units accepted for use with SI to be converted to SI – litres to cubic metres, degrees Celsius to kelvin, minutes, hours and days to seconds, and so on. It would also stop units accepted for use for SI being sufficient as conversion targets - no converting degrees F to degrees C unless also converted to K. I don't think that's your intention and it's not what your first bulletpoint says. NebY (talk) 13:22, 15 August 2024 (UTC)

• I can't tell whether this is meant to apply to scientific articles, or general articles. If the latter, the idea that meters, kilos, and degrees C will be given without conversion is a nonstarter. EEng 17:09, 14 August 2024 (UTC)

  Ah, yes, my wording is definitely muddled. I did not intend to change the circumstances under which units need to be converted, only to say which units we mean by "metric" when we say they can be used without conversion on scientific articles and as conversion targets for articles that use US and imperial units. I will change the phrasing to clarify; further tweaks welcome. -- Beland (talk) 21:54, 14 August 2024 (UTC)

• Generally this reads good to me, impressive work! Though I don't quite understand why it says "metric" – wouldn't "SI" work too? Gawaon (talk) 06:28, 15 August 2024 (UTC)

  @Gawaon: Whilst all SI units are metric, not all metric units are SI. This has been extensively discussed already. --Redrose64 🌹 (talk) 07:30, 15 August 2024 (UTC)

  While that's trivially true, it misses the point. Where in Beland's listing are the non-SI metric units? SI units should usually be preferred, so I just wonder if these non-SI units deserve the treatment suggested for them. Gawaon (talk) 12:57, 15 August 2024 (UTC)

  Liters, hours, Daltons, and decibels, for example are non-SI units accepted for use with the SI, though not all of them are based on units of 10 from the base units. Light years, parsecs, or AU may get added to that. Not all of those are what I think of when I think of the metric system; dalton (unit) doesn't even say that unit is part of the metric system, so maybe "metric" isn't the best terminology, either. -- Beland (talk) 16:29, 15 August 2024 (UTC)

  Dalton (unit)#Adoption by BIPM already correctly describes it as a non-SI unit accepted for use with the SI and the following sections go into more detail. The lead is unhelpful; we don't need another demonstration that Wikipedia is not an RS so I'll fix that. SI's coherence is one of its great virtues compared to earlier metric systems, but metric units have had many relationships with each other. NebY (talk) 16:50, 15 August 2024 (UTC)

  I think it should be fine to talk about "SI units and units approved for use with the SI", especially since we then go on and list all relevant units anyway. So there is no need to mention "metric units". Gawaon (talk) 17:14, 15 August 2024 (UTC)

  If I'm understanding correctly, I find myself agreeing with Gawaon (talk · contribs). All non-SI units should be converted to SI, except those units accepted by BIPM for use with SI. Dondervogel 2 (talk) 13:10, 15 August 2024 (UTC)

  Just so. We shouldn't require degrees C to be converted to K, or insist that mL be converted to m³. We should normally convert °F to °C not K, and fl.oz. to mL is usually enough,but it would be excessive to start specifying pairs. NebY (talk) 13:33, 15 August 2024 (UTC)

  That makes sense. There should also be no requirement to convert logarithmic units like the byte, shannon or decibel to SI. Dondervogel 2 (talk) 18:01, 15 August 2024 (UTC)

  Bytes and shannons are units of information and information entropy. As far as I can tell, they cannot be converted to SI units because they are nonphysical, but are also not accepted for use with the SI. Presumably all English- speaking countries use the same units, so I think we don't need to say anything about those. -- Beland (talk) 20:40, 15 August 2024 (UTC)

  On second thoughts, some variants of the decibel, like the dBm or dBV, really do need conversion, in these two cases into watts and volts, respectively. Dondervogel 2 (talk) 21:46, 15 August 2024 (UTC)

• Beland's fourth bullet Obscure metric units should be linked and defined in basic SI units on first use: rayleigh (R), katal (kat), weber (Wb) is unnecessary and not useful to our readers. Very few who don't understand weber (Wb) will find (kg⋅m²⋅s⁻²⋅A⁻¹) useful; most will find the eruption of gobbledegook into a sentence disruptive. We do want to make the point that Less familar units should be linked on first use, which does sit in the middle of Beland's third bullet about conversion but I think would stand better alone.

That third bullet ends with a long list of units. Do we want such itemisation? It could be summarised instead as "other SI units and units approved for use with SI", "units in SI or approved for use with it", or similar. NebY (talk) 13:56, 15 August 2024 (UTC)

I like that idea. The three units in the last list are used by hardly any articles, so presumably they will explain some amount of more helpful context. If we just say those should be linked like the second list, then the only list we'd need would be the ones that don't need to be linked. -- Beland (talk) 17:29, 15 August 2024 (UTC)

---

(version 2, edited based on below comments)

Change hatnote to:

See also: § Currency conversions, and Wikipedia:WikiProject Astronomy/Manual of Style § Units

Change bullet point and add sub-points:

• For units of measure that are obsolete, obscure outside of a particular specialty or geography (e.g. furlong), or not part of the SI/SI-accepted or US customary systems (e.g. zolotnik), supply a parenthetical conversion into at least SI or SI-accepted units. [...remainder of line unchanged...]
  • Metric units not part of SI or accepted for use with SI should either be replaced with SI or SI-accepted units (e.g. joules instead of ergs), or they should be treated as obscure units in the same way as furlongs.
• Metric prefixes used should be commonly known, namely "pico" thru "tera", preferably in commonly-used combinations (e.g. 2,000 kilometers not 2 megameters).
• (Light-year and parsec and will need to be added depending on the outcome of the RFC.)

Under the bullet point "Units unfamiliar to general readers", add:

• Commonly-known SI and SI-accepted units that can be used without linking are: meter (m), gram (g), second (s), ampere (A), liter (L), Pascal (Pa), hertz (Hz), degrees Celsius (°C), minute (min), hour (h), day (d), degree (of angle, °), volt (V), watt (W)

---

Version 2 above is an attempt to incorporate the above comments. If we accept that as a general rule, it implies there is no need to convert AU to kilometers, though we could add an exception for that later. -- Beland (talk) 18:23, 15 August 2024 (UTC)

I'm not sure I like the part about the AU not being converted all that much, but in general, that draft makes a lot of sense! Gawaon (talk) 18:37, 15 August 2024 (UTC)

This is much tighter, easier to read and easier to use, and sound. I like it. I'm not sure we need "(e.g. in the CGS or MTS systems)" - it could be seen as contradictory, because there is a lot of overlap between SI and those two (metres, (kilo)grams, seconds), but that's about the biggest nit I can pick. AU->km might be an exception, but metrology always has edge cases; better to have a clear core. NebY (talk) 11:54, 16 August 2024 (UTC)

Okey, dropped that parenthetical. -- Beland (talk) 04:55, 17 August 2024 (UTC)

What specifically is meant by the "SI/SI-accepted unit and an intuitive field-specific units" clause? I don't think the link to WikiProject Astronomy is all that helpful here. Maybe it would be possible to list the relevant units right here instead? Gawaon (talk) 06:34, 17 August 2024 (UTC)

Wikipedia:WikiProject Astronomy/Manual of Style#Units has like ten additional points, so I thought it would get less out of sync if it only exists in one place? The relevant units would be radiuses and masses of the Sun, Jupiter, Earth, and Moon; luminosity of the Sun; and standard gravity. Maybe better phrasing would be "Some properties of planets and stars need additional conversions; see Wikipedia:WikiProject Astronomy/Manual of Style#Units"? -- Beland (talk) 20:05, 17 August 2024 (UTC)

Frankly I'm not convinced they need to be mentioned here at all. The important point is that at least a conversion into SI units is present; that they are additionally also expressed in alternative units is not forbidden by our rules. So if that's not mentioned here, but only on the Project Astronomy page, there's no conflict. Gawaon (talk) 20:21, 17 August 2024 (UTC)

By "they" do you mean the specific units to be converted to like "mass of the Sun"? I was assuming this MOS page should at least link to any topic-specific advice related to units, for completeness and ease of navigation. -- Beland (talk) 23:14, 17 August 2024 (UTC)

I'm rather sceptical of linking from this page to the WikiProject since it would seem to make the WikiProject's rules an "official" extension of this guideline, which actually they are not. A "See also" hatnote might be more appropriate and would reduce the risk of giving that impression. Gawaon (talk) 06:36, 18 August 2024 (UTC)

Well, if you ask me, they are just as important to follow, because the consequences will be the same - the project will be inconsistent, and people will potentially be upset and potentially revert your edits. But a "see also" link is fine. I'll edit the draft. -- Beland (talk) 15:17, 18 August 2024 (UTC)

Discussion seems to have died down, so I put the revised-as-above version 2 on the live page, except for the light-years part which is still closing out in the above thread. -- Beland (talk) 05:37, 6 September 2024 (UTC)

Jansky and Rayleigh and friends

The above changes have taken care of a lot of cases (hurray!) but as I was tidying up, I realized some units seem to have fallen through the cracks, namely:

• jansky (jy), rayleigh (R), katal (kat), weber (Wb)

These seem to be the only metric units not approved for use with SI which are nevertheless still in modern use, and awkward to convert into SI units in a way that is easy to understand when presented briefly. I think the new wording of MOS:CONVERSIONS tells us to treat these units "as obscure units in the same way as furlongs" which would require a conversion to SI units. But given the discussion above, it sounds like we don't actually want a conversion, but would be happy with just linking to the defining articles? If so, I assume we can simply add these as exceptions under the light-year/parsec exception? -- Beland (talk) 18:14, 6 September 2024 (UTC)

I'm not sure about katal and weber (their respective articles claim they are both SI units), but jansky and rayleigh are unfamiliar and should be converted to an equivalent SI unit. Dondervogel 2 (talk) 18:41, 6 September 2024 (UTC)

Ah, you're right; katal and weber are both listed on International System of Units as derived units. I totally missed those on the list. The conversions for the others would be:

• 1 jansky (10⁻²⁶ W⋅m⁻²⋅Hz⁻¹)
• 1 rayleigh (1/4π 10¹⁰ photons s^-1 m^-2 sr^-1)

This looks like the "gobbledygook" NebY was objecting to for weber; does that objection also hold for jansky and rayleigh given that unlike weber they are not official SI units? Beland (talk) 19:39, 6 September 2024 (UTC)

The jansky's expression in SI isn't bad, as these things go; it's brief, the units give a fair indication of what sort of quantity's being measured, and the converted values might well be meaningful to those interested. We don't seem to use it often, or if we do we aren't linking it - most of the instances at Special:Whatlinkshere/Jansky seem to be uses of Template:Radio astronomy, and one of the few applications is in the opposite direction a peak X-ray flux density of 2.3×10⁻²³ W/(m²⋅Hz) (2.3×10³ jansky). If someone went wild and inserted SI conversions throughout, at worst it'd cause little offence to editors and little or no difficulty to readers; and it might even be helpful. Let's treat them like furlongs.

The rayleigh's expression looks much more intimidating in either version, using 1/4π sr-1 as above or using extended columns of a centimetre cross-section. We link to it in 9 articles, with actual values in only two. IMAGE (spacecraft) has The sensitivity is 1.9 count/second-Rayleigh. Student Nitric Oxide Explorer has The sensitivity of channel A at 130.4 nm is 23 counts/second/Rayleigh and the sensitivity of channel B at 135.6 nm is 26 counts/second/Rayleigh. Is counts/second/rayleigh equal to 4π^-1 10^-10 m² · steradian counts per photon?? Is it too late to pretend we never heard about it? NebY (talk) 21:30, 6 September 2024 (UTC)

OK, I've added jansky and rayleigh as affirmative examples of obscure metric units that should be converted to SI. The rayleigh equations didn't make much sense to me either in terms of dimensional analysis or visually, so I'll tag those two articles and rayleigh (unit) itself and ask for some help from experts. -- Beland (talk) 00:25, 7 September 2024 (UTC)

The weber (Wb) is one that I learnt at school (but have had little use of it since). It is the SI unit of magnetic flux, and 1.0 Wb = 1.0 V s, or 1.0 J s C^-1, or 1 × 10⁸ maxwell. --Redrose64 🌹 (talk) 20:56, 6 September 2024 (UTC)

Astronomical units

(The discussion wrapped up and resulted in a change to the MOS.)

Another thread recently concluded that units approved for use with the SI do not need to be converted to SI units. Astronomical units (AU) are approved for use with the SI, but there was some sentiment expressed that they should be converted to SI units.

The RFC on very large distances has concluded that light-years should be primary, with conversion to parsecs and not kilometers or foometers. One big objection to kilometers at that scale was that exponential notation would be required to express those quantities, and many readers would find that difficult to understand. Interplanetary distances are small enough that they can be written in familiar words. Pluto currently does that even in its infobox, and it seems to work OK.

Previous discussion resulted in a decision not to use metric prefixes larger than "tera", because they would not be widely understood; planetary systems extend into the petameters, e.g. the heliopause, though most AU distances probably don't. Articles like Makemake currently use Tm.

Which solution are people in favor of?

1. Astronomical units are accepted for use with the SI, and don't need to be converted.
2. Astronomical units should be converted to kilometers using "million", "billion", or "trillion" in both prose and compact environments like infoboxes and tables. Examples:
   • 49.3 au (7.38 billion km)
   • 121,000 au (18.1 trillion km)
3. Astronomical units should be converted to meters using metric prefixes. Examples:
   • 49.3 au (7.38 Tm)
   • 121,000 au (18.1 Pm)
4. Something else.

Presumably we'd flip to using light-years and parsecs before getting over 9,999 trillion km, possibly even before 999 trillion km. A million AU is about 150 trillion km, and going over 1 million AU could be awkward anyway. -- Beland (talk) 19:06, 6 September 2024 (UTC)

I've nothing against light years or AU, but articles should include a converted value to metres with the appropriate prefix that avoids decimal places 49.3 AU (7,380 Gm). A kilometre is after all 1000 metres. Wikipedia educates, the reader can always link to Giga or another prefix to see what it is. We already use Giga or Gibi for computer storage. Avi8tor (talk) 19:29, 6 September 2024 (UTC)

Hmm, Wikipedia:WikiProject Astronomy/Manual of Style#Units recommends km/s for large velocities, like interplanetary spacecraft. It's a bit harder to compare tens of thousands of km/s to Tm instead of billions of km (though obviously a lot easier than miles). -- Beland (talk) 20:22, 6 September 2024 (UTC)

Your option 2 seems like a good balance: trillion is the largest we'd ever really hit (once around 100,000 au we should switch to ly; might be worth putting that in the guidelines!), and I don't see a large benefit in using metric prefixes for million and billion here. I think the point of a converted value is for people to have a value they can try to compare with ordinary life, and "million km" seems easier to do that with than "billion m". Scientific notation probably isn't worth using in prose but might be in info boxes? - Parejkoj (talk) 20:31, 6 September 2024 (UTC)

NOT #3. The point of the conversion is to move out of specialist-speak. Giving two specialist versions is pointless. Johnjbarton (talk) 23:04, 6 September 2024 (UTC)

Option 2 is clear and useful, and we don't really need to worry about expressing anything in trillions of kilometres. Neptune's only about 30 au (4.5 billion km) from the sun and even the heliopause is about 120 au (18 billion km) out. 121,000 au (1.91 ly) is really an interstellar distance, nearly halfway to the nearest star out here in the boondocks, and I wouldn't expect our sources to be using au then. Not #3, it makes reading too much like hard work. NebY (talk) 23:38, 6 September 2024 (UTC)

I must have been reading something other than the heliopause that's 120,000 AU out and got my numbers mixed up. Oort cloud and a couple dozen other articles do use 200,000 AU, 100,000 AU, and 50,000 AU. Comet, for example, actually converts 50,000 AU to light-years.

We could actually advise, say, anything over 10,000 AU should have AU converted to light-years and not kilometers (that's about 0.16 ly). That starts to become a significant fraction of the distance to the nearest star. It would ease the transition from km to light-years; otherwise short distances have AU+km and long distances have ly+pc and there's no way to directly compare them. -- Beland (talk) 00:58, 7 September 2024 (UTC)

My preference would have been to use AU for small (astronomical) distances and pc (or ly) for large ones, with continuity ensured by always converting to SI. I understand Beland's proposal to be: convert AU to km for short distances, AU to ly for middle distances and ly to pc for long interstellar distances. It's a pig's ear but it's probably the best we can do given the (IMO misguided) decision to avoid converting interstellar distances to SI. Dondervogel 2 (talk) 06:42, 7 September 2024 (UTC)

Ah yes, I was forgetting how great comet orbits can be and the hypothesised extent of the Oort cloud. I'm hesitant about giving advice on a transition point (a little like saying when to use inches or feet) or introducing a third conversion pair. My rule-of-thumb might be that in a planetary or in-system context use au/km, in an interstellar one use ly/pc, and if if it should be put in both contexts then consider using not only one context's pair but also the lead dimension from the other (au/km + ly, or ly/pc + au), but sparingly - and there has to be a better way of putting that. NebY (talk) 12:34, 7 September 2024 (UTC)

I concur that we shouldn't have a transition distance, but rather recommend AU for in-system contexts and ly for interstellar contexts. When both contexts are relevant I think it's better to not try to make a rule; Solar system mixes AU, ly, and km in various places, and I think they do a good job. Tercer (talk) 13:03, 7 September 2024 (UTC)

Should we just say something like "where interplanetary and interstellar scales overlap, it is OK to convert between AU and light-years to make distances comparable"? BTW, for clearly interplanetary distances, were you in favor of AU+km or just AU? -- Beland (talk) 16:55, 7 September 2024 (UTC)

I think that's a good solution. As for AU+km or AU, I don't have a strong opinion. 150 million km is on the edge of what can be intuitively grasped, so it can be useful for some readers. I don't think it's worth the clutter, so I'd rather write only AU. But if some editor wants to add the km conversion I won't bother them about it. Tercer (talk) 19:28, 7 September 2024 (UTC)

Personally I'd favour option 2 as most reader-friendly. However, option 1 follows logically from our general rule that "units approved for use with the SI do not need to be converted to SI units", so it would be a reasonable solution too. Gawaon (talk) 06:42, 8 September 2024 (UTC)

Option #4. None of Options #1-3 are compatible with the use of pc/ly for interstellar distances. To avoid inconsistencies, we need overlap between

• large interplanetary distances (in au) and small interstellar distances (in ly/pc), and
• large planetary distances (in km) and small interplanetary distances (in au).

The only way I see to achieve both is to convert au to SI for small interplanetary distances and au to ly/pc for large ones. Dondervogel 2 (talk) 09:02, 8 September 2024 (UTC)

Comment To give some examples for how the latter is currently handled: at a predicted minimum distance of 0.051 parsecs—0.1663 light-years (10,520 astronomical units) (about 1.60 trillion km) (from the lede of Gliese 710); about 52,000 astronomical units (0.25 parsecs; 0.82 light-years) from the Sun (from Scholz's Star); and Semi-major axis 506 AU (76 billion km) or 0.007 ly (from the infobox of Sedna). Renerpho (talk) 22:55, 8 September 2024 (UTC)

The second one looks to me like the MOS-preferred style (other than the choice of units) for a triple conversion and something that naturally comes out of {{convert}}, whereas the other two need some tidying up. The quadruple conversion seems like a bit much. -- Beland (talk) 17:20, 9 September 2024 (UTC)

In the case of the solar system article, it became a bit silly to keep converting distance scales from AU to km. The consensus was to use AU throughout, because the AU is intended for interplanetary scales (whereas km is intended for planetary scales). There is a comment in the early part of the article explaining the term, and that is all that is needed. The comparable conversion used on the asteroid articles is AU and Gm. Praemonitus (talk) 21:57, 9 September 2024 (UTC)

• From the listed options I would go with Option 1 (just use AU), though I could see giving a conversion to either km or m using scientific notation. I have a pretty strong negative reaction to Gm, Tm, etc; I think that's just SI fetishism. I'm fairly sure those units are used at most sparingly in the wild. --Trovatore (talk) 00:17, 10 September 2024 (UTC)

I'd go with Option 1, but most importantly we should use the modern abbreviation au wherever it appears. Wikipedia's usage has been left inconsistent for too long (including in this thread). Skeptic2 (talk) 11:29, 12 September 2024 (UTC)

Fully agree about consistency of symbol (au, not AU). Let's make sure any new guidance reflects that consensus. Dondervogel 2 (talk) 11:55, 12 September 2024 (UTC)

Is that a proposal to delete "Articles that already use AU may switch to au or continue with AU; seek consensus on the talk page." from MOS:UNITSYMBOLS? I use "AU" in conversation because that's what I learned in as an undergrad, but I have no particular preference. -- Beland (talk) 18:00, 12 September 2024 (UTC)

That was not my intention. I just meant that any new statement about astronomical units should follow existing mosnum consensus, which is to use au for the unit symbol. I can't speak for Skeptic2. Dondervogel 2 (talk) 18:06, 12 September 2024 (UTC)

I have no strong preference between au and AU, but I'm less than convinced that this needs to be uniformized across Wikipedia as a whole. The main thing is that it be consistent within any single article, in the spirit of WP:ARTCON. --Trovatore (talk) 18:09, 12 September 2024 (UTC)

Hmm, well, the existing consensus isn't exactly for "au", it's for "au" except where "AU" is consistently established. I intentionally used "au" in the examples because that seems to be the long-term direction we're going, but for consistency with the other recommendation the examples might need to have a note saying "AU" is OK if used consistently throughout an article. On the other hand, if we're adding or removing conversions across the entire project, that would be a good time to standardize on "au". Dropping the "AU" exception would also result in simpler rules. Either way, I'm going to run a script to find non-compliant instances like I did to enforce the new rule that liter uses a capital "L" symbol.

BTW, I was wondering where consensus for the existing guidance was established, and it appears to be Wikipedia talk:Manual of Style/Dates and numbers/Archive 157#Abbreviation for astronomical unit once again. -- Beland (talk) 18:16, 12 September 2024 (UTC)

I prefer option 1, no conversions or optional conversions. 21 Andromedae (talk) 15:27, 14 September 2024 (UTC)

The use of au in place of AU was recommended by the IAU in 2012 and is now adopted by leading professional journals such as MNRAS, ApJ, AJ, etc. Hence au is the internationally recognized abbreviation and should have been adopted by Wikipedia a decade ago.Skeptic2 (talk) 19:00, 12 September 2024 (UTC)

Summing up au

OK, trying to score the opinions above in a reductionist fashion (correct me if I've gotten anything wrong):

• Avi8tor: #3
• Parejkoj: #2
• Johnjbarton: NOT #3
• NebY: #2, NOT #3, for overlap: au+km+ly (and in reverse ly+pc+au)
• Dondervogel2: #2 more or less, for overlap au+km, au+ly+pc
• Tercer: #1 but #2 OK, for overlap: "where interplanetary and interstellar scales overlap, it is OK to convert between AU and light-years to make distances comparable" rather than a specific rule
• Gawaon: #2 but #1 OK
• Praemonitus: #1 for solar system
• Trovatore: #1 but #2 OK, m with scientific notation OK, NOT #3
• Skeptic2: #1

And tallying those up:

• #1: 3 first choice, 1 second choice, 1 for solar system context
• #2: 4 first choice, 2 second choice
• #3: 1 for, 3 explicitly against
• #4: 3 in favor of conversion from au to at least ly to provide overlap

It's pretty clear there is consensus against #3, and it looks like there's a weak preference for #2 over #1. Given the reasons people noted for and against converting au to km, it might make sense to adopt #2 but emphasize the existing "excessive" exception, which will result in #1 in places where I expect people feel strongest that au-only is better.

It seems we favor "au" over "AU", so I'll use that in examples. I'm doing some database scans and will ask about removing "AU" as an allowed unit as a separate question once I have some numbers.

It also seems like there's support for having overlapping but not rigidly specified ranges between km, au, and ly, so readers can make appropriate comparisons. Exactly how to do that was a bit unclear, but for the sake of operationalizing this, I'll make a specific proposal. (If people have strong feelings, feel free to discuss.) The previous RFC decided to convert ly to pc, and there might be some objections if ly are used and pc are not (though astronomers also use au). It also decided not to convert between km and ly, partly because of comprehensibility problems with overly-large quantities of km, so maybe we should avoid doing that. Which would also mean the same units would be used no matter whether au or ly were primary, which is kind of nice. So the overlapping units on the high end would be au, ly, and pc, with either ly or au primary.

So, how about adding this as another "Generally...except" bullet point after the "light-years" exception:

• Astronomical units (au) should be converted to kilometers (km) using "million", "billion", or "trillion" in both prose and compact environments like infoboxes and tables. When large interplanetary-scale distances overlap with small interstellar-scale distances, convert au to ly and pc, or ly to pc and au (depending on context). Examples:
  • 49.3 au (7.38 billion km)
  • 121,000 astronomical units (1.91 light-years; 0.59 parsecs)
  • .9 ly (0.28 pc; 57,000 au)

and add "articles like Solar system where many interplanetary distances are given" to the list of examples on the "excessive" exception. -- Beland (talk) 03:26, 13 September 2024 (UTC)

Thank you for taking the time to do this. You have captured my position well in your summary. Dondervogel 2 (talk) 05:52, 13 September 2024 (UTC)

I think the last example should read "0.9 ly" since we don't do 0-dropping. Otherwise I like it! Gawaon (talk) 06:11, 13 September 2024 (UTC)

Oh man, well spotted. I have a script to fix that very thing, and am sad to have not noticed that. So make that:

0.9 ly (0.28 pc; 57,000 au)

— Preceding unsigned comment added by Beland (talk • contribs) 17:57, 13 September 2024 (UTC)

Added to the MOS page; further tweaks welcome if anyone notices anything else amiss. -- Beland (talk) 23:00, 13 September 2024 (UTC)

Guidance at APPROXDATE for completely unknown ranges

At risk of instruction creep... currently MOS:APPROXDATE has guidance for various partially unknown date ranges. It doesn't say anything about when everything is unknown, presumably because most editors simply omit it when there's nothing to say. However, it seems there are lists which have say a birth / death range as a standard inclusion per row, and some editors might be tempted to throw in an empty range to mark that the range is not included. There doesn't appear to be MOS guidance for this case, currently.

My suggestion to add:

If both extremes of a range are unknown but a c. or fl. marker is inappropriate, omit the range entirely. Do not use ?–? or ????–????. This is true even if part of a section that normally includes such a range, e.g. a list of people with their birth and death dates. In the rare scenarios where such a range is important to include anyway, use (unknown) or (disputed) if there are referenced scholarly sources saying it is flat unknown or a debate, but do not use these if the dates merely haven't been found in sources consulted so far, such as for obscure people or organizations.

This would basically make "omit it" the default. Thoughts / alternative ideas? Would this be a useful inclusion? (Or alternatively does anyone want to argue we should suggest something different for this case, e.g. using "(unknown)" even when it might be known, just not to the Wikipedia editors at the moment?) SnowFire (talk) 22:04, 10 September 2024 (UTC)

• Two points:
  • The issue isn't specific to dates or date ranges. It could be any data in a table, so I'm not sure it's a dates-and-numbers issue specifically.
  • The advice to say unknown or disputed is good, but my intuition is this isn't something that MOS should opine on (not yet, anyway) -- see WP:MOSBLOAT. Has there been controvery about this on multiple articles currently?

EEng 23:27, 10 September 2024 (UTC)

I'm honestly not sure if it comes up particularly often. It came up recently at a FLC discussion and I realized there didn't appear to be a "standard" to settle the matter. I'm sensitive to CREEP concerns and if we want to just file this one away as a "wait for a 2nd person to complain", that's fine by me - just figured the first person to raise the matter might still be a useful signal. SnowFire (talk) 09:14, 11 September 2024 (UTC)

Strong oppose the proposal. This comes up all the time if you are writing about medieval and earlier people and events. Obviously you still have include something. It's completely ridiculous to say dating should be suppressed just because we don't know if, for example, someone was born in 1105 or 1109, or some date in between! But there's no point in another finely-tooled set of instructions which most will ignore. MOS:APPROXDATE is already rather too long and over-prescriptive. Johnbod (talk) 15:34, 21 September 2024 (UTC)

Estimated or approximate non-dates?

We generally don't use c.  (etc.) for figures other than dates, even in places we would happily use the English word around. Would it be appropriate to explicitly mention options for non-dates such as est. , approx. , and associated templates somewhere? Both the attempted use of circa for non-dates, as well as general confusion on the matter seem at least semi-frequent. Remsense ‥ 论 05:36, 21 September 2024 (UTC)

Circa or c. is mostly used for dates, but there is nothing in its meaning to make it only for dates. Making a new rule (on top of our already too many) seems unnecessary for me. SchreiberBike | ⌨  00:49, 22 September 2024 (UTC)

I agree there shouldn't be any new provisions, but use of c. or circa for anything but dates, years, etc. will strike readers as very awkward. I'd challenge you to find any non-time usage in high-quality sources. EEng 01:24, 22 September 2024 (UTC)

That would seem an etymological fallacy to me: the very existence of the narrower convention where it is used only for dates means that other uses trying to treat it as a perfect synonym of around are actively awkward to read; it is a wrong usage. With that made clear, I would object that this is likely MOS creep: approximated and estimated figures are important and common, and editors routinely express a general lack of understanding for how best to present them. Remsense ‥ 论 00:58, 22 September 2024 (UTC)

Wait... you're objecting to your own proposal as WP:MOSCREEP? EEng 01:24, 22 September 2024 (UTC)

No, sorry: I was objecting to Schreiber's concern of MOSCREEP. Remsense ‥ 论 01:27, 22 September 2024 (UTC)

So you meant to say something more like "I object to the characterization of this as MOSCREEP"? Under that assumption, I disagree (with you), until (per MOSCREEP, which -- ahem -- I wrote) there's evidence that this issue has been a problem on multiple pages. Is there? EEng 01:44, 22 September 2024 (UTC)

You are correct. There's definitely classes of articles where this is a problem; I'll see what I can do. Remsense ‥ 论 01:46, 22 September 2024 (UTC)

Like the cat who ate some cheese then stood outside a mouse hole, I wait with baited breath. EEng 02:47, 22 September 2024 (UTC)

Recent edits

A string of edits by Jc3s5h and JMF. introducing and removing changes to Wikipedia:Manual of Style/Dates and numbers § Common mathematical symbols, raise issues that I believe should be discussed.

1. The most recent change, permalink/1247903136, has the comment This page does not cover matrix operations., however, I do not see anything in the article to support a restriction to numerical operations.
2. The most recent change reinstates the link to dot product, despite the comment.
3. There seems to be disagreement on the division sign.

The questions that I wish to raise are

1. Should that section mention {{tmath}} or <math>...</math>?
2. Are vector operations within the scope of the article? Regardless of the answer, the dot and cross products should be treated consistently.
3. Should there be two new rows for dot and cross product?
4. Should there be a row for tensor product?
5. Is obelus unhelpful since it has three forms?
6. Should the Division sign (U+00F7 ÷ DIVISION SIGN) be deprecated in favor of Slash (U+002F / SOLIDUS)?
7. Should U+2215 ∕ DIVISION SLASH be explicitly deprecated in favor of Slash?
8. Should the use of "x" and "*" as multiplication signs be explicitly deprecated in favor of U+00D7 × MULTIPLICATION SIGN?
9. Should that section show the LaTeX markup for characters in addition to the HTML character entity references?

-- Shmuel (Seymour J.) Metz Username:Chatul (talk) 10:52, 27 September 2024 (UTC)

1. I think the page should be devoted to general articles, and <math> should be reserved for advanced math and science articles.
2. Vector operations are not currently in the scope of the project page, and I'm not thrilled about adding them.
3. Dot product and cross product should certainly not be addressed in the same row as any scalar operation. The multiplication dot should certainly not be linked to the "Dot product" article nor should the multiplication cross be linked to the "Cross product" article.
4. Tensor products should not be covered in this project page because they're too advanced.
7. I'm not willing to spend 5 or minutes figuring out what this line means.
8. The asterisk as a multiplication sign should be limited to articles about computer languages that use it as such.
9. LATEX should not be mentioned, since we don't use it in Wikipedia. This isn't a style manual for writing outside of Wikipedia.

Jc3s5h (talk) 19:45, 27 September 2024 (UTC)

Tbh, I wondered what this extensive list is doing in the MOS in the first place. Glossary of mathematical symbols does it better. It really needs to be reduced to cover only those symbols that have a styling issue: scalar division and multiplication.

• The grade-school division sign should be formally deprecated, for reasons explained at division sign.
• The 'ordinary' slash (002F) should be preferred over 2215, same logic as straight quotes and curly quotes.
• I prefer U+00D7 × MULTIPLICATION SIGN over x, for biology as well as math but maybe that needs debate.

𝕁𝕄𝔽 (talk) 20:04, 27 September 2024 (UTC)

Comments:

• I see no good reason to prohibit using a division sign to express division. That seems absolutely fine. The division sign article seems to say it might be confusing in Italian, Russian, Polish, Danish, Norwegian, or Swedish, but this is the English Wikipedia. We use points as decimal separators also, and we use commas as a thousands separator too, although that might be confusing in other languages.
• I also see no good reason to prohibit using an asterisk for multiplication; it seems well-understood, easy to type, unambiguous, and common in practice. I agree with not using "x" for multiplication, although I think it's OK to express "by" relationships for 2x4 lumber, 4x8 sheets of plywood, and 4x4 trucks.
• <math>x</math> (i.e., $x$) looks different from ''x'' (i.e., x), and those look different from {{math|''x''}} (i.e., x), at least on my screen, and seeing mixtures of those in the same article can be a bit annoying (especially if they are near each other).

—⁠ ⁠BarrelProof (talk) 21:46, 7 October 2024 (UTC)

Asterisk means convolution (which is somewhat related to the idea of "multiplication" but should not be confused with the usual multiplication). Its use as a substitution for "×" or "⋅" is a bad habit from the old days of poor technology (but it was never used as such in professional typesetting) and has no excuse nowadays. — Mikhail Ryazanov (talk) 22:12, 7 October 2024 (UTC)

Convolution would only be a matter to consider in very mathematically sophisticated specialized contexts. It's not something most people have ever encountered. Even for those who use it, it would often be expressed using summation or integration instead. —⁠ ⁠BarrelProof (talk) 22:21, 7 October 2024 (UTC)

I don't think that this is a good reason to make exceptions to tolerate/promote sloppy typography (moreover, in some computer fonts the ASCII asterisk looks more like a superscript than a binary operator consistent with +, −, = and so on).

I don't think we should feel responsible for how Wikipedia is rendered in all possible fonts. We should remember that everyone is supposed to be able to edit Wikipedia articles. In an article that isn't about mathematics, or at least isn't using it beyond the 10th grade level, f = 1.8 * c + 32 seems basically OK to describe conversion from degrees C to degrees F. It's tricky enough that we tell people to pay attention to the difference between "-", "–", "—", and "−", and to not use italics for the numbers in that formula, although I support those instructions. —⁠ ⁠BarrelProof (talk) 03:37, 8 October 2024 (UTC)

Nobody should complain about otherwise good edits that include "lazy" typography. Those edits are 100% OK and a net improvement to Wikipedia. Other editors who care about typography and MoS can clean up the markup and character choices later. Wikipedia is a collaborative project. Indefatigable (talk) 15:46, 8 October 2024 (UTC)

Using an asterisk to represent multiplication is programming language syntax; I don't think this is common or even well-known among non-programmers. isaacl (talk) 01:47, 20 October 2024 (UTC)

I agree we should discourage use of "*" as a multiplication symbol. I agree it's easy to type, so if one editor writes "y = m*x + c" in an otherwise correct edit, the response should not be to revert that edit, but to replace it with "y = mx + c" or other approved alternative. Dondervogel 2 (talk) 10:40, 20 October 2024 (UTC)

Misleading shortcut

Wikipedia:Manual of Style/Dates and numbers#Common mathematical symbols indicates that its shortcut is "MOS:COMMONMATH", but in fact MOS:COMMONMATH links to Wikipedia:Manual of Style#Common mathematical symbols (a different section on a different page, although partially covering the same topic), which also indicates "MOS:COMMONMATH" as its shortcut. Perhaps one of them must be renamed. — Mikhail Ryazanov (talk) 00:47, 7 October 2024 (UTC)

@Mikhail Ryazanov: I have traced it to this edit nearly two years ago by SMcCandlish (talk · contribs), which I have reverted. The two redirects MOS:COMMONMATH and WP:COMMONMATH were created on the same day in January 2014 (although about twenty hours apart), the first by BarrelProof (talk · contribs) and the second by Wavelength (talk · contribs) following this discussion. It seems that they were intentionally different - and have remained so ever since. If one of them should be repurposed to match the other after ten years, we would need a WP:RFD. --Redrose64 🌹 (talk) 09:00, 7 October 2024 (UTC)

There must've been something that happened to instigate creation of those on the same day, but I have no recollection of it. —⁠ ⁠BarrelProof (talk) 09:17, 7 October 2024 (UTC)

You'd observed that there are two MOS sections on the symbols and suggested merging them, Wavelength responded that both locations are appropriate and we could have two shortcuts instead, and no-one else said anything. NebY (talk) 11:26, 7 October 2024 (UTC)

Thanks for the refresher. I think the two sections ought to at least mention each other in hatnotes, if not be merged. I just added the mentions. It is confusing that both of them are part of the MOS and both of them are sections of the MOS with the same heading: "Common mathematical symbols". Maybe they should become MOS:COMMONMATH1 and MOS:COMMONMATH2?? Is there some way to express the difference between the purposes of those two? I notice that one of those is part of Wikipedia:Manual of Style/Dates and numbers but says nothing at all about dates and numbers, so I suggest that it be merged into the other one. Mathematics is not synonymous with numbers. That section is about expressing operations and relationships and formatting variable names, not numbers. —⁠ ⁠BarrelProof (talk) 17:50, 7 October 2024 (UTC)

Better with hatnotes, yes. Though mathematics != numbers, MOSNUM seems the natural place where readers might look for guidance on the symbols; after all, the less mathematically sophisticated we are, the more likely we are to think of the operators as things we use with numbers. I'd expected that MOSNUM would be more detailed but there's extra content in MOS too, so that's not a useful distinction. The chatty one and the formal one? NebY (talk) 20:10, 7 October 2024 (UTC)

Usually having "MOS:FOO" and "WP:FOO" go to two different places is fine; the very reason we have the "MOS:FOO" pseudo-namespace for MoS shortcuts is that MoS pages were sucking up too many of the mnemonically meanful shortcut strings in which "WP:FOO" would for more editors bring to mind some non-MoS "WP:"-namespace material. Yes, use a disambiguation hatnote as needed; we have those for a reason. However, in this case, both targets are MoS sections, so both shortcuts should go to the same place, presumably the more detailed material. If the stuff at Wikipedia:Manual of Style#Common mathematical symbols is simply a nutshell summary of Wikipedia:Manual of Style/Dates and numbers#Common mathematical symbols (which is probably the case and should be the case) then the former needs no shortcut at all.  — SMcCandlish ☏ ¢ 😼  06:04, 8 October 2024 (UTC)

Discourage postfix plus?

(motivated by the previous section) If there's any work to be done with combining/rearranging MOS:COMMONMATH and WP:COMMONMATH, can we please also add that "over N" and "at least N" should use the standard notation >N and ≥N respectively (as, for example, the CMOS tells in 3.83 and 12.16) instead of a postfix plus (N+, which is ambiguous, inconsistent with other cases like <N and ~N, and doesn't seem to conform to any reputable style guide)? — Mikhail Ryazanov (talk) Mikhail Ryazanov (talk) 21:29, 7 October 2024 (UTC)

Has this issue come up a lot? EEng 22:12, 7 October 2024 (UTC)

A while ago I've got a revert with a suggestive edit summary (that particular article has changed a lot since then, but I still stumble upon similar examples from time to time – if needed, I can put some effort to find specific examples). Also, a simple search for insource:/[0-9]\+ / prefix:: yields thousands of results (before timing out), only a small fraction of which are legitimate uses (or poorly formatted binary operations). — Mikhail Ryazanov (talk) 22:54, 7 October 2024 (UTC)

Then the next question is: has time been wasted debating this question on multiple articles, or can they just be fixed on sight without fuss? If the latter, then no new MOS provision is needed, and therefore it is needful that there not be one. EEng 23:10, 7 October 2024 (UTC)

Numerals in a sequence

'Phase 1' or Phase one'? This appears to be a case that's not explicitly covered.

The AP Stylebook recommends using figures for sequences in its section on "Numbers": "Also use figures in all tabular matter, and in statistical and sequential forms", from which I infer that for sequences, such as 'phase 1', figures should be used for clarity and consistency.

Similarly, chapter 9 of The Chicago Manual of Style advises using figures when referring to a sequence.

I propose adding similar explicit advice to this section of the MOS.

-- Jmc (talk) 20:10, 19 October 2024 (UTC)

• As usual, what's needed before something's added to MOS is examples of this being an issue on multiple articles -- see WP:MOSBLOAT. Are editors not able to work this out for themselves on individual articles? Anyway, why does the word "Phase" need this in particular? Why not "Section" and "Part" and any other words like that?
  The advice from APA and CMS are great if you're making up a new sequence for your thesis, but that's not us. It's hard to imagine an article using a phrase like "Phase 1" or "Phase One" on its own -- that is, other than in imitation of the phrasing of sources. So follow the sources; for example, Economic Stabilization Act of 1970 refers to Phase I and Phase II and Phase III., because that's the form the Act uses. We're not going to override that in the name of consistency with other, unrelated articles. EEng 22:00, 19 October 2024 (UTC)

  To clarify: I'm using 'Phase' purely as an example. The issue of using figures for sequences applies to any sequence. including 'Section' and 'Part' - and other examples: "Game 3", of a sequence of nine; 'Chapter 9' of a sequence of 24; 'Week 4' of a limitless sequence.

  I raise this issue in the context of differing editorial practices in the British Post Office scandal article, where both figures and words have been used to reference the same phases and weeks of the inquiry. I sought guidance from the MOS and found none.

  I'd be content to follow the sources, without adding bloat to the MOS, if I could be confident that that's an accepted stylistic convention in this instance. -- Jmc (talk) 22:27, 19 October 2024 (UTC)

  Such names are very often established by authoritative sources and constitute proper names; we should follow the sources rather than renaming them. Per EEng, we only need a MOS guideline if our sources don't provide clear names and either there is dissent among editors or consistency across articles would be of significant benefit. In the Post Office case, I see the phases have been titled Phase 1, Phase 2 etc by the inquiry[5] so unless the inquiry's inconsistent, we can follow that source. Still, I see that this is a live issue at that British Post Office scandal article, so it would be wrong to establish a new guideline or issue some sort of MOS talk-page ruling without the knowledge of the other editor; pinging MapReader. NebY (talk) 14:56, 20 October 2024 (UTC)

  Between May 1966 and December 1989, multi-episode Doctor Who stories could have titles in any of the four combinations of (i) "Episode ..." or "Part ..."; (ii) numbers as figures or as words. The decision as to which format to use was probably in the hands of the series producer, but in our articles about each story, we give the actual title shown on screen - except that where the on-screen title is all-capitals, we reduce it to title case. Certain Doctor Who reference books do the same, so we're following the sources. --Redrose64 🌹 (talk) 18:18, 20 October 2024 (UTC)

  The question raised was "differing editorial practices in the British Post Office scandal article". Sounds like a matter of internal consistency, which is different. For all manner of things -- this being one IMO -- we might not need consistency among articles, but it does look bad within articles. Surely we already have a rule addressing that general issue tho? Herostratus (talk) 13:24, 21 October 2024 (UTC)

  I think we don't. In articles on TV series it's common to have expressions like "season 3" and "episode 7", which seem to go against our current wording (use words for numbers below 10). Gawaon (talk) 16:37, 21 October 2024 (UTC)

  It is indeed a matter of internal consistency and it does look bad, as Herostratus says. Within the one article (British Post Office scandal), we have (e.g.) both "Phase 3 hearings" and "Phases five and six". Is there in fact a rule addressing this general issue? -- Jmc (talk) 18:47, 21 October 2024 (UTC)

  From Wikipedia:Manual of Style/Dates and numbers#Numbers as figures or words: "Comparable values nearby one another should be all spelled out or all in figures, even if one of the numbers would normally be written differently." Unless you are dealing only with series with fewer than 10 seasons each with fewer than 10 episodes, it is more in line with MOS to give all season and episode numbers in digits rather than words. --User:Khajidha (talk) (contributions) 13:15, 22 October 2024 (UTC)

  True, but series with less than ten seasons aren't all that rare, and there are also miniseries with less than ten episodes. Gawaon (talk) 16:39, 22 October 2024 (UTC)

  Whether or not it's in line with MOSNUM, we frequently – I suspect in the vast majority of cases – give series/season and episode numbers in digits. I've been dipping into Wikipedia:Good articles/Media and drama#Television. Articles on individual episodes do routinely begin e.g. " the ninth and final episode of the first season" but with digits in the infobox. Articles on a season/series list episodes using digits, and articles on a show list series/seasons and episodes with digits, regardless of whether there are more or less than ten, in keeping with the examples in Wikipedia:Manual of Style/Television#Episode listing. Articles are often titled <show> season <n> where n is a digit, never a word, in accordance with Wikipedia:Naming conventions (television)#Season articles. Sampling our WP:Featured articles#Media, I see the same treatment in titles, infoboxes, and listings.

  I very much doubt that editors would accept changes to those FAs and GAs to bring them into line with MOS:NUMERAL, that FA and GA assessors will start to apply MOS:NUMERAL in such cases, that any move requests would succeed, or that MOS:TV and WP:TVSEASON will be brought into line with the current MOS:NUMERAL. Changing MOS:NUMERAL might be easier. NebY (talk) 08:20, 23 October 2024 (UTC)

  I agree, a small addition to MOS:NUMERAL might be a good thing. Gawaon (talk) 17:00, 23 October 2024 (UTC)

  Your final sentence doesn't follow from your statement. It would be more in keeping with the MOS to give all in words. MapReader (talk) 11:16, 23 October 2024 (UTC)

μs vs us

Which style I should use for micro seconds? Does μs relative to "Do not use precomposed unit symbol characters"? DungeonLords (talk) 04:44, 30 October 2024 (UTC)

The 2 characters "μ" and "s" are just fine. The precomposed symbols advice is to guard against particular fonts that combine them into a single character because many software readers for the sight impaired do not know all of these symbols.  Stepho  talk  04:53, 30 October 2024 (UTC)

Day, date month format

Greetings and felicitations. I assume that such constructions as "Wednesday, 24 February" are discouraged, but I can't find it in the text or the this page's archives. (The comma seems unnecessary to me.) May I please get confirmation or refutation? —DocWatson42 (talk) 04:28, 4 November 2024 (UTC)

• MOS:DATEFORMAT and MOS:BADDATE cover the allowed and disallowed formats. Unless the day of the week is vitally important then we leave it out.  Stepho  talk  06:16, 4 November 2024 (UTC)

  This specifically regards the "Hadaka Matsuri" article, and its Konomiya Hadaka Matsuri infobox, which includes the days of the week. —DocWatson42 (talk) 07:40, 4 November 2024 (UTC)

  Ah, the mysterious East. EEng 08:06, 4 November 2024 (UTC)

• Salutations and hugs and kisses to you too.
  • If your question is whether day-of-week should be gratuitously included with dates for no particular reason, the answer is No. That is, if the day-of-week is somehow relevant to the narrative, sure, include it, but otherwise no.
  • Assuming we're in some situation where (per the preceding) inclusion of day-of-week is indeed justified, maybe your question is how to append the D.O.W.
    • If the date is February 24 or February 24, 2024, then without doubt the right format is Wednesday, February 24 or Wednesday, February 24, 2024.
    • According to "Elite editing" [6] (whoever they may be -- search the text "inverted style" on that page), the corresponding answers for 24 February and 24 February 2024 are Wednesday, 24 February and Wednesday, 24 February 2024. To me that does seem right -- Wednesday 24 February 2024 (all run together, no commas at all) seems intolerable.

The question naturally arises as to whether MOS should offer advice on all the above. My answer, as usual, is provisionally No, per WP:MOSBLOAT. EEng 08:02, 4 November 2024 (UTC)

Looking at the article, the date is the 12th day of the Chinese year and the day of the week has no significance. I would remove the day of the week from all those dates in the infobox. For what it's worth, I spent most of the 1990s in Hong Kong/China. Major holidays based on the Chinese calendar treat the day of the week in the same way that we treat the day that Christmas falls on.  Stepho  talk  09:18, 4 November 2024 (UTC)

Okay—will do. Thank you both. ^_^ —DocWatson42 (talk) 09:21, 4 November 2024 (UTC)

The new 18th edition of The Chicago Manual of Style gives advice about commas in dates in ¶ 6.14. When giving examples they mostly give examples with words after the end of the date so the punctuation at the end of the date is illustrated. Some examples:

• The hearing was scheduled for 2:30 p.m. on Friday, August 9, 2024.
• Monday, May 5, was a holiday; Tuesday the 6th was not.

Jc3s5h (talk) 16:56, 4 November 2024 (UTC)