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over-agressive auto-archiving[edit]

It is bad that talk page sections of this article about a timeless long term matter are being agressively auto-archived.- (talk) 14:31, 21 September 2015 (UTC)

The most recent few sections should never be auto-archived, regardless of how old they are.- (talk) 14:43, 21 September 2015 (UTC)

exact time[edit]

The article says 2015 autumn equinox will be at UT 8:20. But the referenced source says 8:21, and various other sources say x:22. Why the discrepancy/variation? Is this event not one precise instant for the whole Earth? What is the true exact time, to at least the second? What is the most reliable source?- (talk) 14:41, 21 September 2015 (UTC)

2015 sep Equinox: 2015-Sep-23 08:20:33.876[edit]

It is very difficult to find the exact times of solstices and equinoxes, to better than a minute of resolution -- and therefore hard to resolve discrepancies in various sources.

This source has a handy any-year calculator that gives
TDT = Wed, 23 Sep 2015 08:21:33 GMT
UTC = Wed, 23 Sep 2015 08:20:06 GMT
but the footnotes explain that these times are only approximate, to about a minute of accuracy (and the following shows them to be about a half-min off).
This is the best discussion of how hard it is to obtain exact times, and how to get them from an online NASA calculator:

Using that engine yields:

Ephemeris Type [change] :     OBSERVER
Target Body [change] :     Sun [Sol] [10]
Observer Location [change] :       Geocentric [500]
Time Span [change] :       Start=2015-09-23 08:20:30, Stop=2015-09-23 08:20:40, Intervals=20
Table Settings [change] :          QUANTITIES=30,31
Display/Output [change] :          default (formatted HTML)
2015-Sep-23 08:20:33.000        68.182392 179.9999901   0.0002366
2015-Sep-23 08:20:33.500        68.182392 179.9999957   0.0002366
2015-Sep-23 08:20:34.000        68.182392 180.0000014   0.0002366
2015-Sep-23 08:20:34.500        68.182392 180.0000071   0.0002366
Date__(UT)__HR:MN:SC.fff            CT-UT    ObsEcLon    ObsEcLat

Which leads to:

2015-Sep-23 08:20:32.876        68.182392 179.9999887   0.0002366
2015-Sep-23 08:20:33.876        68.182392 180.0000000   0.0002366
2015-Sep-23 08:20:34.876        68.182392 180.0000113   0.0002366
The dynamical Coordinate Time scale is used internally. It is equivalent to the current IAU definition of "TDB".

Giving a final result of:

2015-Sep-23 08:20:33.876 UTC (+68.182392 = CT/TDB)

In conclusion, 8:20:34 and 8:21 UTC is the proper rounded time, 8:20 is understandable -- but 8:22 seems somewhat wrong, for any general usage.- (talk) 21:49, 21 September 2015 (UTC)

The Horizons output indicates UT; it does not say if that is UT1 or UTC. According to the US Naval Observatory the prediction is that UT1-UTC = 0.24414 second on 23 Sept. Can you indicate where it is stated whether Horizons considers UT to mean UT1 or UTC? Jc3s5h (talk) 15:47, 22 September 2015 (UTC)
I was able to answer my own question. According to HORIZONS User Manual
is Universal Time This can mean one of two non-uniform time-scales based on the rotation of the Earth. For this program, prior to 1962, UT means UT1. After 1962, UT means UTC or "Coordinated Universal Time". Future UTC leap-seconds are not known yet, so the closest known leap-second correction is used over future time-spans.
Jc3s5h (talk) 15:53, 22 September 2015 (UTC)


In discussing the determination of the date of the equinox, Equinox § Date observes that "the leap year intervals in [Pope Gregory's] calendar were not smooth (400 is not an exact multiple of 97)", but does not explain the significance of these numbers. The Gregorian leap-year cycle is 400 years long and contains 97 leap years (every fourth year, but not in century years xx00 unless xx is a multiple of 4). Needs clear explanation, which the foregoing is not very. --Thnidu (talk) 08:29, 22 September 2015 (UTC)

Lede too detailed[edit]

I've read it like 10 times and I still don't understand what the equinox is. Outedexits (talk) 21:01, 2 November 2015 (UTC)

I will simplify it Outedexits (talk) 22:30, 2 November 2015 (UTC)