Talk:Julian year (astronomy)

message: 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)
thread_title: Request for Comment

message: 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)
thread_title: Decision

message: 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)
replies: text: 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)
thread_title: Intro improvement

message: 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)
replies: text: 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)
thread_title:  Julian calendar distinguished 

message: 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)
replies: text: 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)
replies: text: Thanks. I'm glad it wasn't just me!   — Aldaron • T/C   17:04, 22 October 2012 (UTC)
thread_title:  Angular measure? 

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thread_title:  External links modified