are the same length. Their names exist because they are the days with
the longest period of daylight and shortest period of daylight. The word solstice is a corruption of 2 latin words that mean sun and stand.
The days when this occurs are known as the Summer Solstice, about June 21, and the Winter
Solstice, about December 21. These dates/days do vary, and so does the time of whichever day.
Very basically the Earth revolves round the Sun, also the Earth's axis is tilted
relative to the Sun at 23.45°. The relative tilt of the Earth's varies to the supposed axis of the Sun
as we progress through the year.
In what we call an Earth day the earth apparently rotates roughly once so we see sunrise in
what we call the morning and sunset in what we call the evening.
There are 365 days in a year, so every year we have a new cycle - not that simple though because
it is closer to 365¼ days per year which is why every 4th year we add the odd ¼ s together to give
an extra day which is of course our leap year. If we didn't make this basic adjustment, every 700 or so
years the winter would be in the summer, and the summer in the winter.
Even that is not exact and every so often a leap second has to to be added
to adjust that small but increasing inaccuracy.
With the respective movements of Sun and Earth at these significant times during the year the
northern and southern hemispheres are nearer the Sun, or the Sun is further north or south.
In the northern hemisphere, when the Sun is furthest north in June at the time of the Summer
Solstice the Sun is overhead at latitude 23° 27' north, also known as the Tropic of Cancer.
There is no convienient arrangement to make a precise adjustment to our year every year so as they
roll by the actual time of the of the Solstice actually becomes slightly early until adjustment of the leap year moves it
back. The consequence of this is that a summer solstice on June 22 will gradually change to June 21 and earlier,
a winter solstice from December 22 to December 21 and earlier.
Even after the leap-year adjustments take effect you begin to see over many years a
change of solstice time which is demonstrated in the graph below.
Leap year adjustments usually take place when the year, such as 1988, is divisible by
4. However the rule for leap years when a century occurs, such as 1900, is that it must be exactly divisible
by 400 and 1900 is not, whereas 2000 is and therefore allows the solstice to slip further forward in
the year. If there had been no leap year adjustment the date/time would be even earlier.
An apparent anomaly in all of this is that the Sun does not set at its latest on the
longest day or at its earliest on the shortest day. The reason is complex and revolves around the
Sun's reduction or increase of the interval of the Sun's transit and setting, and also of the change
of the equation of time. It all balances out.
It should be noted that the times in the graph are Greenwich Mean Time and take no account
of the annual change to the outdated British Summer Time, which should be made permanent as British
Standard Time. Changing back and forth between GMT and BST does of course mean the last Sunday in
March has 23 hours and the last Sunday in October has 25 hours.
We have created a table below to show the Summer Solstice, the Winter Solstice, and both
Vernal and Autumnal Equinoxes. The Equinox is in fact the point when the Sun passes over the Equator.
Since there are so many variables to all of this, it should be stressed there is no
absolute date/time for any of these events and different algorithms give slightly differing results,
so we presume to say no table is spot-on, just close.
Year | | Vernal equinox | | Summer solstice | | Autumnal equinox | | Winter solstice |
| | | Date | Time | | Date | Time | | Date | Time | | Date | Time |
| |
2000 |
| Mar.20 | 07:26 |
| Jun.21 | 01:37 |
| Sep.22 | 17:12 |
| Dec.21 | 13:25 |
2001 |
| Mar.20 | 13:15 |
| Jun.21 | 07:25 |
| Sep.22 | 23:01 |
| Dec.21 | 19:15 |
2002 |
| Mar.20 | 19:04 |
| Jun.21 | 13:13 |
| Sep.23 | 04:49 |
| Dec.22 | 01:04 |
2003 |
| Mar.21 | 00:53 |
| Jun.21 | 19:01 |
| Sep.23 | 10:38 |
| Dec.22 | 06:54 |
2004 |
| Mar.20 | 06:42 |
| Jun.21 | 00:49 |
| Sep.22 | 16:26 |
| Dec.21 | 12:43 |
2005 |
| Mar.20 | 12:31 |
| Jun.21 | 06:37 |
| Sep.22 | 22:15 |
| Dec.21 | 18:33 |
2006 |
| Mar.20 | 18:20 |
| Jun.21 | 12:25 |
| Sep.23 | 04:03 |
| Dec.22 | 00:22 |
2007 |
| Mar.21 | 00:09 |
| Jun.21 | 18:13 |
| Sep.23 | 09:52 |
| Dec.22 | 06:12 |
2008 |
| Mar.20 | 05:58 |
| Jun.21 | 00:00 |
| Sep.22 | 15:40 |
| Dec.21 | 12:02 |
2009 |
| Mar.20 | 11:47 |
| Jun.21 | 05:48 |
| Sep.22 | 21:29 |
| Dec.21 | 17:51 |
2010 |
| Mar.20 | 17:36 |
| Jun.21 | 11:36 |
| Sep.23 | 03:17 |
| Dec.21 | 23:41 |
2011 |
| Mar.20 | 23:25 |
| Jun.21 | 17:24 |
| Sep.23 | 09:06 |
| Dec.22 | 05:30 |
2012 |
| Mar.20 | 05:14 |
| Jun.20 | 23:12 |
| Sep.22 | 14:54 |
| Dec.21 | 11:20 |
2013 |
| Mar.20 | 11:03 |
| Jun.21 | 05:00 |
| Sep.22 | 20:43 |
| Dec.21 | 17:09 |
2014 |
| Mar.20 | 16:52 |
| Jun.21 | 10:48 |
| Sep.23 | 02:31 |
| Dec.21 | 22:59 |
2015 |
| Mar.20 | 22:41 |
| Jun.21 | 16:36 |
| Sep.23 | 08:20 |
| Dec.22 | 04:48 |
2016 |
| Mar.20 | 04:30 |
| Jun.20 | 22:24 |
| Sep.22 | 14:08 |
| Dec.21 | 10:38 |
2017 |
| Mar.20 | 10:19 |
| Jun.21 | 04:12 |
| Sep.22 | 19:57 |
| Dec.21 | 16:27 |
2018 |
| Mar.20 | 16:08 |
| Jun.21 | 10:00 |
| Sep.23 | 01:45 |
| Dec.21 | 22:17 |
2019 |
| Mar.20 | 21:57 |
| Jun.21 | 15:48 |
| Sep.23 | 07:34 |
| Dec.22 | 04:07 |
2020 |
| Mar.20 | 03:46 |
| Jun.20 | 21:36 |
| Sep.22 | 13:22 |
| Dec.21 | 09:56 |
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