Talk:September equinox

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Equinox on September 21[edit]

This equinox will occur on September 21, 2096 in UTC and so the changre just made by an anonymous editor is justified. Karl (talk) 12:08, 20 August 2014 (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.

  • stellafane.org/misc/equinox.html
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).
  • www.survival.org.au/solstice2013.php
This is the best discussion of how hard it is to obtain exact times, and how to get them from an online NASA calculator:
  • ssd.jpl.nasa.gov/horizons.cgi
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.-96.233.20.34 (talk) 21:37, 21 September 2015 (UTC)

more precise Solstice and Equinox times[edit]

The English speaking world seems to be limited to approximate Solstice and Equinox times, to about the nearest minute.
The French offer a more precise, to the second, master table:

  • fr.wikipedia.org/wiki/Mod%C3%A8le:Solstice-%C3%A9quinoxe
2013       20      11:01:55        21      05:03:57        22      20:44:08        21      17:11:00
2014    20      16:57:05        21      10:51:14        23      02:29:05        21      23:03:01
2015    20      22:45:09        21      16:37:55        23      08:20:33        22      04:47:57
2016    20      04:30:11        20      22:34:11        22      14:21:07        21      10:44:10
2017    20      10:28:38        21      04:24:09        22      20:01:48        21      16:27:57
2018    20      16:15:27        21      10:07:18        23      01:54:05        21      22:22:44
Références :   mars • juin • sept. • déc.
Institut de mécanique céleste et de calcul des éphémérides

Most WP readers do not care about this -- but some might like access to the more accurate times. How can we provide such access in a good way? Would we ever want to replace our template master table with a more-precise master table of times? -71.174.188.32 (talk) 19:14, 22 December 2015 (UTC)