Wednesday, December 5, 2012

Earliest Sunset!

Here we are on the 5th of December, a good 2 weeks till the Winter Solstice, and yet, if you look at a table of sunset times, right now is the time of earliest sunset!  "Wait", I can hear you all say - "I thought that happened on the first day of Winter on 21 December!"  Well, you would be partly right - the shortest DAY occurs on the first day of Winter in the northern hemisphere, when the sun follows its lowest arc across the sky.  Referring back to that table of sunset/sunrise times, you will also note that the date of latest sunrise occurs in mid-January, a couple weeks AFTER Winter Solstice.  So the shortest day happens on 21 December, but because the Earth's orbit is not completely circular, but slightly elliptical, the earliest sunset, latest sunrise and shortest day do not all fall on the first day of Winter.  If it did, life would be a little more boring, and we wouldn't be able to use these tidbits as excuses to learn something new.  But do go check out those sunrise/sunset times - you will see I'm right!  You can think of it this way - with the sunset time getting later day by day, it won't be long till the Winter that isn't here yet will give way to Spring and Summer!
Oh, and the picture above - taken a couple months ago from Kitt Peak National Observatory with my little Meade Telescope - an 80mm diameter apochromatic refractor, F/6, with a 480mm focal length and Canon XSi camera.

1 comment:

Anonymous said...

Haha... SOME of us other folks up a bit norther in the Northern Hemisphere than ya'll in Tucson actually have winter. :-P

(Mokpo/Gwangju just got our first snow of the year last night, in fact!) :D