Tuesday, December 1, 2009

His Dark Environment

The winter here gets very dark. This is not surprising considering how far north we are. Despite our relatively mild winters (courtesy of the Gulf Stream) we are far north of even Quebec City.

The shortest day of the year, the winter solstice, December 21st --- is a date celebrated in one way or another by most cultures on earth. On this day, London only gets 7 hours and 50 minutes of sunlight – substantially less than New York which gets 9 hours 15 minutes. On the other hand, if you happen to live in Oslo, you only get 5 hours 53, and if you live in Svalbard you won’t see the sun at all from the end of October til mid February.

However, surprisingly, the solistice is not the day when the sun sets the earliest, or rises the latest. In New York, the earliest sunset is actually December 8th and the latest sunrise is January 4th. As you get further north, these two dates get closer together: Here in London, the earliest sunset is December 12th and the latest sunrise is December 29th.

At one point in graduate school I remember pondering the geometry of why this happens --- which has to do mainly with the angle of the earth with respect to its orbital plane (if I remember correctly). I think it was my friend Dave Morin who managed to figure it out --- not surprisingly he just finished writing a classical mechanics textbook with a ton of really hard problems in it.

8 comments:

Nuntiya said...

I never knew this. I've always counted down to Dec. 21st - if I can make it to this date, then it would all get better again. But I see it's more complex than that. Now I have to decide what's more important to me, a late sunrise or an early sunset. Hmmm.

Steve said...

To avoid wrestling with this issues, the ancient Egyptians all decided to winter in Florida.

jennienyc said...

The ancient Britons, perhaps. The ancient Egyptians didn't have to wrestle with this problem at all, seeing as they were already at the same latitude as Florida.

Steve said...

Of course I meant that the Egyptians did not go to Britain for vacation....

Susanne said...

The upside: If you happened to be in Oslo today, you could watch a beautiful sunrise and a breathtaking sunset from the *same* side of the physics building -- without having to come in early or work late... :)

Steve said...

http://curious.astro.cornell.edu/question.php?number=208

This is a really good explanation..

Carissa Aoki said...

This isn't completely related, but if you've ever wondered how the earth's orbit, axis, etc. operate on MUCH MUCH longer time scales, see: http://en.wikipedia.org/wiki/Milankovitch_cycle.

Steve said...

Thanks Carissa -- this is very cool!