SAD sufferers rejoice! Contrary to what you might expect, the earliest sunset of the year doesn't occur on the shortest day of the year. In London at least, the earliest sunset of the year occurs today. Honest.
Tomorrow's sunset in London really will be later than sunset this afternoon, even if only by a few seconds. Check out a list of sunset times for London and you'll see that the time of sunset gets gradually earlier each day until today, and then gradually later again. Conversely the time of sunrise gets gradually later each day until New Year's Eve, and then gradually earlier again. Halfway between these dates comes the shortest day, December 21st (a day on which, spookily, both sunrise and sunset are getting later).
Date
Sunrise
Sunset
Date
Sunrise
Sunset
Dec 6
07:50
15:52
Dec 25
08:05
15:56
Dec 9
07:54
15:52
Dec 28
08:06
15:58
Dec 12
07:57
15:51
Dec 31
08:06
16:01
Dec 15
08:00
15:52
Jan 3
08:06
16:04
Dec 18
08:02
15:53
Jan 6
08:05
16:08
Dec 21
08:04
15:54
And why does this happen? The short reason is because the meridian (the time at which the Sun is highest in the sky) changes subtly each day, with the most rapid changes occurring in December. For example, the time at which the sun crosses the meridian changes by a full ten minutes between 16th December (sun highest at 11:56) and 6th January (sun highest at 12:06).
The long reason for these changes is a combination of the Earth's orbit being an ellipse, not a circle, and the Earth being tilted at an angle of 23½º to its orbit around the Sun. These two independent functions combine to create something called the equation of time, and it's this that causes 'noon' in the sky to differ from noon on a clock. • more on the equation of time(very straightforward) • more on the equation of time(fairly straightforward) • more on the equation of time(a bit more scientific) • more on the equation of time(scarily mathematical, but very pretty) • more on the equation of time(daily differences for London)
The date of the earliest sunset varies from place to place, according to how far from the equator that place is. London's earliest sunset may be today, but Edinburgh's is not until Thursday, Madrid's was last Friday and Sri Lanka's was as long as three weeks ago.
The time of the earliest sunset also varies considerably. On the equator sunset never gets any earlier than 17:47, local time. This earliest time gets earlier as you move further north - for example 17:19 at 20ºN, 16:34 at 40ºN and 14:53 at 60ºN. And above the Arctic Circle (66½ºN) there are of course winter days when the Sun never rises at all.
You can explore the wonderful world of global sunset and sunrise times on the two sites below (both fairly straight-forward, don't panic): • Sunrise/Sunset World Reckoner(ooh that's clever) • Sunrise/Sunset calculator
(Southern hemisphere readers please ignore the above, and just enjoy your lovely long summer days instead)
