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How about that…


Posted by Nate in Bike Commuting, Weather.
Tuesday, January 8th, 2008 at 7:59 am

I’ve been noticing as I leave work that my bike lights seem less and less necessary since it’s been so much brighter. At first I thought maybe it was the snow reflecting more light, but it’s also definitely been staying lighter later.

I was confused since I noticed this about a week ago and the solstice had only just passed – how can it be this much brighter already? And why is the morning still so darn dark if the days are really getting that much longer?

Turns out (and I’m fuzzy on the exact details) that it’s got something to do with the tilt of the earth and the fact our solar orbit is an ellipse rather than a circle. Basically, the sunrise times and sunset times move slightly out of sync. If you graph them they still look sort of like sine waves, but they’re shifted just out of phase.

Our sunrises continue to be later (darker longer) all the way through December 27th, almost a week after the solstice, but our sunsets start getting later (lighter longer) on December 10th! The combination of movement puts our shortest day (and everyone’s) on the 21st, but I never really did the figuring to realize how differently the sunrise and sunsets change.

And now it’s in your brain, too.

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5 Responses to “How about that…”

  1. Rick Says:
    January 8th, 2008 at 9:00 am

    Nate – I knew that sunrise and sunset changed differently, and that even after the solstice, the morning sunrise got later. But I didn’t realize that the days started getting longer so much before the solstice. Amazing how these things happen and we’re only sort of aware.

  2. Nate Says:
    January 8th, 2008 at 10:46 am

    Hmm, sorry if that was confusing. The total length of daylight does what you think – shrinking until the solstice and then growing after – so that’s still the shortest day, but the WAY it happens is different. It’s stealing light off the morning for longer than it is in the evening, and you start to gain light back in the evening before you gain it back in the morning.

  3. sls Says:
    January 8th, 2008 at 3:24 pm

    Hmmm – this post makes me think of 2 things.
    ONE) I am way jealous that you leave work early enough to notice this — I have not observed these changes from my basement cube.
    TWO) This explains daylight savings time a little – because even we get night light, we still need morning light, so we have to change the clocks!

  4. troy Says:
    January 9th, 2008 at 12:39 pm

    Ah, the level of posts not under “beer” can be quite educational. :)

  5. troy Says:
    January 14th, 2008 at 4:37 pm

    By the by, is there a way to “subscribe” to a blog and just get notified when a new post is made?