Thursday, December 20, 2007

Winter Solstice 2007 - shortest day equinox, first day of winter

A solstice occurs twice a year, whenever Earth's axis tilts the most toward or away from the Sun, causing the Sun to be farthest north or south at noon. The name is derived from Latin sol (sun) and sistere (to stand still), because at the solstice, the Sun stands still in declination, that is, its movement north or south is minimal. The term solstice can also be used in a wider sense as the date (day) that such a passage happens. The solstices, together with the equinoxes, are related to the seasons. In some languages they are considered to start or separate the seasons; in others they are considered to be center points (in English, in the Northern hemisphere, for example, the period around the June solstice is known as midsummer, and Midsummer's Day is 24 June, about three days after the solstice itself).

Paul Winter's Winter Solstice Celebration in New York: a world music celebration of the return of the light after winter. In the Cathedral of St. John the Baptist at the 28th Annual Winter Solstice Celebration on 13, 14 and 15 December 2007


To calculate the date and approximate time of the vernal and autumnal equinoxes and of the summer and winter solstices you can use this online calculator. This is based upon the formulas given by Jean Meeus in his Astronomical Algorithms but without corrections for perturbations, so that the times may differ from the true times by up to 20 minutes.

Start year and End year specify the range of years you're interested in. Only years in the range -100 CE through 4000 CE can be used with this calculator.

The End year box may be left blank. E.g., to get the dates and times for the year 1970 enter "1970" into the Start year box (and click on Submit). This produces:

  Vernal equinox        Summer solstice       Autumnal equinox        Winter solstice
1970-03-21 00:55 1970-06-21 19:39 1970-09-23 10:57 1970-12-22 06:39

These are Gregorian (Common Era) Calendar dates.

Dates for a range of years may be obtained, e.g. for all years in the range 2000 through 2010:

  Vernal equinox        Summer solstice       Autumnal equinox        Winter solstice
2000-03-20 07:26 2000-06-21 01:37 2000-09-22 17:12 2000-12-21 13:25
2001-03-20 13:15 2001-06-21 07:25 2001-09-22 23:01 2001-12-21 19:15
2002-03-20 19:04 2002-06-21 13:13 2002-09-23 04:49 2002-12-22 01:04
2003-03-21 00:53 2003-06-21 19:01 2003-09-23 10:38 2003-12-22 06:54
2004-03-20 06:42 2004-06-21 00:49 2004-09-22 16:26 2004-12-21 12:43
2005-03-20 12:31 2005-06-21 06:37 2005-09-22 22:15 2005-12-21 18:33
2006-03-20 18:20 2006-06-21 12:25 2006-09-23 04:03 2006-12-22 00:22
2007-03-21 00:09 2007-06-21 18:13 2007-09-23 09:52 2007-12-22 06:12
2008-03-20 05:58 2008-06-21 00:00 2008-09-22 15:40 2008-12-21 12:02
2009-03-20 11:47 2009-06-21 05:48 2009-09-22 21:29 2009-12-21 17:51
2010-03-20 17:36 2010-06-21 11:36 2010-09-23 03:17 2010-12-21 23:41

If you are interested in the dates and times after every nth year then you can specify a Period value. E.g., here are some values for years whose difference is 33:

  Vernal equinox        Summer solstice       Autumnal equinox        Winter solstice
1799-03-20 14:16 1799-06-21 12:01 1799-09-23 01:36 1799-12-21 18:23
1832-03-20 14:13 1832-06-21 11:23 1832-09-23 01:19 1832-12-21 18:39
1865-03-20 14:10 1865-06-21 10:45 1865-09-23 01:01 1865-12-21 18:55
1898-03-20 14:07 1898-06-21 10:07 1898-09-23 00:43 1898-12-21 19:11
1931-03-21 14:04 1931-06-22 09:29 1931-09-24 00:25 1931-12-22 19:26
1964-03-20 14:01 1964-06-21 08:51 1964-09-23 00:06 1964-12-21 19:41
1997-03-20 13:59 1997-06-21 08:13 1997-09-22 23:47 1997-12-21 19:57
2030-03-20 13:56 2030-06-21 07:35 2030-09-22 23:27 2030-12-21 20:12
2063-03-20 13:54 2063-06-21 06:57 2063-09-22 23:07 2063-12-21 20:26
2096-03-19 13:52 2096-06-20 06:19 2096-09-21 22:47 2096-12-20 20:41

As noted above, the time calculated by this program is ephemeris time (a.k.a. terrestrial dynamic time or TDT). To get an estimate of GMT to within about fifteen minutes adjust by the appropriate value of delta-T (which is currently about one minute, so no modification is needed for years in the 20th or 21st centuries). For dates around 1000 CE actual times GMT may have been about a half-hour earlier than the times given, and for dates around 1 CE about three hours earlier.


If dates in the Julian Calendar are needed then there is PC software available to do the same as the online calculator except that it gives dates in both the Julian and the Gregorian Calendars.

The VE.EXE program calculates the approximate date and time of the vernal and autumnal equinoxes and of the summer and winter solstices. This program uses the same formulaes given by Jean Meeus in his Astronomical Algorithms as are used by the online calculator, so the results are the same. The times are ephemeris times.

VE.EXE should be run from a DOS command line (see Running Console Applications from Windows). When run with no command line parameters it displays the required command line syntax:

VE.EXE, Version 2.0, Copyright 2000 Hermetic Systems
This program calculates dates of equinoxes and solstices.
Use: VE start_year [end_year]
Range of years: -100 through 4000

The parameter end_year may be omitted. E.g., to get the dates and times for the year 1970 use "VE2 1970", which produces:

 Vernal equinox      Summer solstice     Autumnal equinox    Winter solstice
1970-03-21 G 00:55, 1970-06-21 G 19:39, 1970-09-23 G 10:57, 1970-12-22 G 06:39
1970-03-08 J 00:55, 1970-06-08 J 19:39, 1970-09-10 J 10:57, 1970-12-09 J 06:39

Note that dates are given in both the Gregorian (Common Era) Calendar and in the Julian Calendar.

Dates for a range of years may be obtained, e.g. for all years in the range 2000 through 2010:

 Vernal equinox      Summer solstice     Autumnal equinox    Winter solstice
2000-03-20 G 07:26, 2000-06-21 G 01:37, 2000-09-22 G 17:12, 2000-12-21 G 13:25
2000-03-07 J 07:26, 2000-06-08 J 01:37, 2000-09-09 J 17:12, 2000-12-08 J 13:25
2001-03-20 G 13:15, 2001-06-21 G 07:25, 2001-09-22 G 23:01, 2001-12-21 G 19:15
2001-03-07 J 13:15, 2001-06-08 J 07:25, 2001-09-09 J 23:01, 2001-12-08 J 19:15
2002-03-20 G 19:04, 2002-06-21 G 13:13, 2002-09-23 G 04:49, 2002-12-22 G 01:04
2002-03-07 J 19:04, 2002-06-08 J 13:13, 2002-09-10 J 04:49, 2002-12-09 J 01:04
2003-03-21 G 00:53, 2003-06-21 G 19:01, 2003-09-23 G 10:38, 2003-12-22 G 06:54
2003-03-08 J 00:53, 2003-06-08 J 19:01, 2003-09-10 J 10:38, 2003-12-09 J 06:54
2004-03-20 G 06:42, 2004-06-21 G 00:49, 2004-09-22 G 16:26, 2004-12-21 G 12:43
2004-03-07 J 06:42, 2004-06-08 J 00:49, 2004-09-09 J 16:26, 2004-12-08 J 12:43
2005-03-20 G 12:31, 2005-06-21 G 06:37, 2005-09-22 G 22:15, 2005-12-21 G 18:33
2005-03-07 J 12:31, 2005-06-08 J 06:37, 2005-09-09 J 22:15, 2005-12-08 J 18:33
2006-03-20 G 18:20, 2006-06-21 G 12:25, 2006-09-23 G 04:03, 2006-12-22 G 00:22
2006-03-07 J 18:20, 2006-06-08 J 12:25, 2006-09-10 J 04:03, 2006-12-09 J 00:22
2007-03-21 G 00:09, 2007-06-21 G 18:13, 2007-09-23 G 09:52, 2007-12-22 G 06:12
2007-03-08 J 00:09, 2007-06-08 J 18:13, 2007-09-10 J 09:52, 2007-12-09 J 06:12
2008-03-20 G 05:58, 2008-06-21 G 00:00, 2008-09-22 G 15:40, 2008-12-21 G 12:02
2008-03-07 J 05:58, 2008-06-08 J 00:00, 2008-09-09 J 15:40, 2008-12-08 J 12:02
2009-03-20 G 11:47, 2009-06-21 G 05:48, 2009-09-22 G 21:29, 2009-12-21 G 17:51
2009-03-07 J 11:47, 2009-06-08 J 05:48, 2009-09-09 J 21:29, 2009-12-08 J 17:51
2010-03-20 G 17:36, 2010-06-21 G 11:36, 2010-09-23 G 03:17, 2010-12-21 G 23:41




2010-03-07 J 17:36, 2010-06-08 J 11:36, 2010-09-10 J 03:17, 2010-12-08 J 23:41

As with the online calculator, the times calculated by this program are ephemeris times. The source code for this program is in VE.C.

VE.EXE requires a 32-bit Intel PC. Together with the VE.C source code it may be downloaded from this site as VE.ZIP (23,024 bytes). This software may be used freely by individuals for personal, non-commercial purposes.

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