Talk:Julian year (astronomy)

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Requested move[edit]

Reason: to reverse an unsupported renaming

Add *Support or *Oppose followed by an optional one sentence explanation, then sign your vote with ~~~~
  • Support The disambiguation link in the original article is sufficient Nike 22:26, 4 October 2005 (UTC)[reply]
  • Support. Perhaps the recently (today) created Julian year (calendar) should be a separate article under that title or perhaps it should be renamed or perhaps it should be merged into Julian calendar; however the title Julian year should be given to the astronomy article and Julian year (disambiguation) would list Julian year (calendar) if that article is retained under that name. The Julian year is in actual current usage as a time unit in astronomy (fundamentally a way to measure days, not years), whereas the Julian calendar is not in any actual current usage. Until today, the astronomy article was at Julian year, and that ought to be restored. -- Curps 03:43, 5 October 2005 (UTC)[reply]
  • Oppose. The problems caused in the historical record because of alterations to the start of the julian year, is at least as vaild a topic as the use of the Julian year in astronomy. Philip Baird Shearer 08:44, 5 October 2005 (UTC)[reply]
  • Oppose, per Philip Baird Shearer. "Current usage" does not automatically establish more notability. —Lifeisunfair 02:13, 15 October 2005 (UTC)[reply]

Discussion[edit]

Add any additional comments

Although I originally suggested the move and (incorrectly) tried to implement it, I am pursuaded by another that it would not be appropriate. The original article was replaced by a disambiguation page, which links to this article and another which does not exist, Julian year (calendar). The latter subject is covered an existing article, Julian calendar. Since this is already covered by a disambiguation link, a disambiguation page is unnecessary. See discussion on the original talk page. --Nike 22:26, 4 October 2005 (UTC).[reply]

I see that now. I am thinking that probably it does not need an article separate from Julian calendar. However, the first sentence is, "A Julian year is of 365.25 days long." This is factually incorrect. A year of the Julian calendar is either 365 or 366 days long, never 365.25 days. A better one would be, "A Julian year is a period beginning on January 1 and ending on the following December 31 on the Julian calendar, which is either 365 or 366 days long, depending upon whether the given year is a leap year." --Nike 03:17, 5 October 2005 (UTC)[reply]

The whole point of the previous discussion (and the new article) is that the Julian year has not always started on 1 January. The times when countries changed is important information for anyone who is interested in history because changes in dates caused by the move over to the Gregorian calender is only one of the complications. Another is that the recorded year of an even may be different in an historical source because the source may use a different date for the start of the year. Philip Baird Shearer 08:44, 5 October 2005 (UTC)[reply]
BTW I think the changes made to this article in the 12 hours (since it was moved) has made it a far better article. Philip Baird Shearer 10:49, 5 October 2005 (UTC)[reply]
If you wish to create an article about what day was considered the first day of the year, then "Julian year" is hardly the clearest title for it. This is not the first thing that would spring to mind. First day of the year would make more sense, or New Year's Day, or something similar. In fact the topic could be expanded to non-Western calendars to flesh out a full article (see for instance [1].
Also, I suspect the start date of March 25 was not universal. It certainly seems to have applied to Britain and its colonies, but in Ancient Rome the year apparently started on either March 1 or January 1, and according to this fairly detailed page:
In his excellent book Marking Time Duncan Steel remarks (p.165) that it is often claimed that part of the Gregorian reform consisted in setting the first day of the year (New Year's Day) to January 1st, but that in fact the papal bull made no reference to the date of New Year's Day. January 1st was already New Year's Day in many European countries.
So it seems the starting day of the year was not an inherent property of the Julian calendar but varied on a country-by-country basis, which again would make First day of the year or some such a more appropriate title than Julian year (calendar). -- Curps 17:01, 5 October 2005 (UTC)[reply]
It is not just the start of the year which is of interest, it is also the ordinal of the year. Different times have started their calendar from different years. I am no expert on the Roman period and I look forward to more contributions on the subject. This is also something which happens in later times as well when people date their correspondence from the date of the start of a reign, but that is much easier calculate because the start of their reign is usually agreed upon and widely disseminated, although working out the saint's day can be tricky. Philip Baird Shearer 09:07, 6 October 2005 (UTC)[reply]

The year-number is also not an inherent part of the Julian calendar, unlike the Gregorian. It was first instituted in Roman times, when the years were named for consuls, and later the reigns of emperors, so it is not just "something which happens in later times". AUC dates were used mostly by historians. Various other methods have also been used. AD dates only came into general use much later, and are also used with the Gregorian calendar. So the Julian year is independent of any method of counting years. This already discussed in the Anno Domini article, so there is no point on duplicating the information, nor would it be the most appropriate place. What would there be in Julian year (calendar) article that is not already covered by other articles? --Nike 20:32, 6 October 2005 (UTC)[reply]

Request for Comment[edit]

This still appears on the request for comment list so I'll add my two cents. I doubt it's a significant inconvenience to astronomers to click on the disambiguation link. However, an amateur history buff with an interest in Napoleon's invasion of Russia would find it confusing to reach the astronomy page by accident. Encyclopedias are references for laypeople. Durova 18:06, 8 November 2005 (UTC)[reply]

Decision[edit]

It was requested that this article be renamed but there was no consensus for it be moved. (proposal was to move to to Julian year) Ryan Norton T | @ | C 13:01, 15 October 2005 (UTC)[reply]

Intro improvement[edit]

The intro first explains the Julian astronomical year technically, then everything that a julian year isn't, up to including confusing a bit, but why such a rigid Julian year concept? What use? I believe the truth is that it was needed for the astronomical epochs: the tropical year varied somewhat by planetary perturbations and the varying ellipticity of Earth's orbit around the Sun, so an astronomical year couldn't be used. Later developments have also shown that a day isn't well enough defined, therefore JD and epochs based on JD are moving to rely on ephemeride time ET, so that we get JDE and epochs based on JDE, otherwise the physics involving celestial mechanics will contain systemic errors. ... said: Rursus (mbork³) 11:36, 25 August 2009 (UTC)[reply]

In general you are correct, although any such reason seems more appropriate in the Usage section which follows the lead. The Julian year replaced the variable Besselian year used before 1984, per the IAU (1976) System of Astronomical Constants. However, both Terrestrial Time (the new name for Ephemeris Time) and Universal Time (variable Earth time) are used with it. TT (atomic time on Earth's geoid) is used for calculating the motions of solar system bodies (in two forms if relativity is included, TCB and TCG), but that time is useless for events on Earth, which requires UT (in two forms, UT1 (mean solar time at Greenwich) and UTC (atomic time with leap seconds). For example, whether a solar eclipse will occur on Earth is calculated using TT, but to determine where and when it will occur on the surface of the Earth UT is needed. — Joe Kress (talk) 17:05, 25 August 2009 (UTC)[reply]

Julian calendar distinguished[edit]

This sentence in the intro has several problems:

Astronomers follow the same calendar conventions that are accepted in the world community: They use the Gregorian calendar for events since its introduction on October 15, 1582 (or later, depending on country), and the Julian calendar for events before that date.

"Astronomers" can be taken to mean modern astronomers, or all astronomers who were active after 1582. I have no idea what calendar an English astronomer would have used to record an event in 1700. I think the truth is that astronomers use many different calendars from one minute to the next, depending on whether they are creating an ephemeris, writing the date of a contemporary observation, researching historical observations, or scheduling telescope time. Jc3s5h (talk) 16:42, 17 February 2012 (UTC)[reply]

I reviewed a few published texts, specifically planetary tables, that is, tables that predict the position of the Sun, Moon, and planets. Ephemerides and almanacs only give their positions for a few years in the future at most. If they are intended for an international audience, they might use both calendars after 1582, or give conversion instructions. Ptolemy, Theon, and Copernicus used Egyptian years of 365 days each. I assume medieval Arabic astronomers used the tabular Islamic calendar. Only after the introduction of the Gregorian calendar do we find dates given in the Julian calendar in planetary tables. Kepler ignored the Gregorian calendar — he only uses Julian dates in his Rudolphine Tables (1627). In his Tables astronomiques (1740), Jacques Cassini used the Gregorian calendar after 1582 and the Julian calendar for earlier dates, as expected since France adopted the Gregorian calendar in 1582. Similarly, in his Tables of the Sun (1898), Simon Newcomb used the Gregorian calendar after 1600, the Julian calendar before 1500, and either during 1500–1600, even though the United States as a British colony adopted the Gregorian calendar in 1752. Newcomb does not allow a Julian date between 1600 and 1752. The Royal Society was founded in 1660 so its published records would be useful. — Joe Kress (talk) 05:15, 20 February 2012 (UTC)[reply]

Angular measure?[edit]

Are the tropical and sidereal years reversed in the discussion of "angular measure"? If not, some clarification is in order. — Aldaron • T/C 13:14, 22 October 2012 (UTC)[reply]

That passage was gibberish. The article by Simon et al. is 21 pages long and isn't really about the Julian year or the length of any of these years. Expecting someone to understand that passage (if it has any meaning, which I doubt) without a reference to a specific page and equation or table is completely unreasonable. I deleted the passage. Jc3s5h (talk) 13:44, 22 October 2012 (UTC)[reply]
Thanks. I'm glad it wasn't just me! — Aldaron • T/C 17:04, 22 October 2012 (UTC)[reply]

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