The Equinox is Not Quite Equal

Yep, today is the spring equinox. But its not quite equal amounts of day and night. Checking the Weather Underground for Tucson yields 12 hours and 6 minutes from sunrise to sunset.

So where does that extra six minutes come from? The equinox would be equal day and night if Earth were a perfect sphere and had not atmosphere. Refraction effects due to Earth's atmosphere lengthen our day a bit. The exact amound depends on somewhat on your latitude. For instance, in Anchorage the day will be 12 hours and 10 minutes long tomorrow and at Barrow, Alaska 12 hours and 15 minutes.

NASA is celebrating with a Sun-Earth Day Webcast at 1:00pm edt. Enjoy the equinox, even if it isnt' quite equal.

Reprinted with permission from the Half-Astrophysicist Blog.