Talk:Q577

Definition of year

A year is not necessarily associated with a solar year. Consequently most definitions are plain wrong. GerardM (talk) 10:18, 23 December 2013 (UTC)

• At least ru:Год is about unit of measurement that ≈365 days. So for example galactic year (Q268391) is not subclass of year (Q577). — Ivan A. Krestinin (talk) 11:26, 23 December 2013 (UTC)
  • It follows that the Russian article is not about the same concept as the others. Consequently it needs its own item. GerardM (talk) 21:28, 24 December 2013 (UTC)
    • This is general problem: very large part of items links similar but not strongly equals terms. This problem is often mentioned in P31/P279 discussions. I saw some links in this item, all contains definition that is similar to ru:Год, so I do not see reasons to disconnect ru:Год from Q577. I think then we need some strongly defined term for P31/P279 hierarchy it is better to create new "clear" item then use existing items with many sitelinks and as the result many near but different meanings. — Ivan A. Krestinin (talk) 22:15, 24 December 2013 (UTC)

I added the statement different from (P1889): calendar year (Q3186692), Julian year (Q217208), common year (Q235729). That should make it a bit clearer. --Arctic.gnome (talk) 17:19, 31 August 2016 (

Shouldn't a year be a subclass of a unit of time (Q1790144), rather than an instance of a unit of time? -- Alexzabbey (talk) 13:16, 31 December 2019 (UTC)

Conversion to SI

@Infovarius: Changed conversion to SI unit (P2370) to duration (P2047) because converting to SI units has a constraint violation with unit without standard conversion to SI (Q21684377). Because the orbit of the Earth is not exactly the same every year, it cannot be perfectly converted to SI. --Arctic.gnome (talk) 17:17, 31 August 2016 (UTC)

Ok. But may be we should increase error then? --Infovarius (talk) 12:23, 1 September 2016 (UTC)

If you look at w:Year#Sidereal, tropical, and anomalistic years you will see that all three of these years could be considered the period of the Earth's orbit about the Sun, depending on what reference point you adopt for the beginning and end of the orbit. The range of these values is about 0.0174 days, which is about 1500 seconds. I agree the precision should be changed, and a reference to a reliable source should be provided. Jc3s5h (talk) 13:51, 18 June 2017‎

Conversion value removed

I removed the recently added value conversion value, 31,556,925.9747 ephemeris seconds, because no reference is supplied, and because there are several kinds of years which are accurately described by the item's description "orbital period of the Earth around the Sun" and this value could only apply to one of them. This issue is discussed in the two talk page sections above. Jc3s5h (talk) 13:38, 23 April 2018 (UTC)

@Jc3s5h: You can find "31 556 925.9747" in w:en:Ephemeris_time#Redefinition_of_the_second and https://books.google.co.jp/books?id=uJ4JhGJANb4C&pg=PA80. And why do you believe 31558000 seconds is the only true conversion value for 1 year? --Okkn (talk) 14:39, 23 April 2018 (UTC)

I just noticed that while the value for duration, 31,558,000±1,000 second, correctly included a tolerance, the value for conversion to standard unit did not. I have corrected this oversight. I believe 1000 seconds is the correct tolerance because it contains the various reasonable interpretations of "orbital period of the Earth around the Sun" that can be found in the table "Lengths of principal years" on page C2 of the Astronomical Almanac for the Year 2017 prepared by the US Naval Observatory and Her Majesty's Nautical Almanac Office. The relevant years are the tropical year, sidereal year, and anomalistic year. The eclipse year is also listed, but I don't believe it falls with the description of this item. Jc3s5h (talk) 14:51, 23 April 2018 (UTC)

@Jc3s5h: Why do you adopt only the value provided in Astronomical Almanac (Q1815913), and not the one defined in ISO 80000-3: Quantities and units—Part 3: Space and time (Q17005431)? In the ISO definition, 1 a = 365 d or 366 d. --Okkn (talk) 15:12, 23 April 2018 (UTC)

I do not have a copy of Astronomical Almanac (Q1815913), and no library near me has a copy. I won't rely on a source I can't read. But infer from your restatement of the definition, "1 a = 365 d or 366 d", that it refers to a Gregorian calendar year. We don't seem to have a separate item for Gregorian calendar year, but if we did, it would be a subclass of calendar year (Q3186692).

There are many calendars that attempt to model the revolution of the Earth about the Sun, for example, the ancient Egyptian calendar (Q254101). I drew the line at modern scientific measurements that are all considered valid ways of measuring the revolution of the Earth around the Sun; I disregarded cruder approximations, including all calendars that can only measure ± 1 day, at best. If we want to include all solar and lunar-solar calendars, the tolerance would have to be around a month. Since calendar year (Q3186692) contains the property subclass of (P279) year (Q577), it seems to me we either need to include all solar calendar years, or none of them. It seems to me the use of different from (P1889) for common and leap year indicates we are excluding calendar years. So maybe the calendar year item should not be indicating it is a subclass of year. Jc3s5h (talk) 16:15, 23 April 2018 (UTC)

Here is a link to the page from the almanac that gives the duration of several kinds of years. Jc3s5h (talk) 17:24, 23 April 2018 (UTC)

Page from Astronomical Almanac for the Year 2017 which gives, among other things, the duration of several kinds of years.