Rate of Change of Day Length
Hello there, This question is regards to changes in sunrise/sunset
times. I understand how they work, but surely the amounts by which the times
differ on a day to day basis depend on the time of year. I would expect for the
greatest change to be around March 21st and September 21st as they are the
opposite days from the solstices. Does the rate of change of time depend on
what rate the angle is changing between the earth's tilt and the sun?
You got that right! the greatest change in daily sunset and sunrise times is
around the equinoxes each year. However the tilt angle changes from 22.1 to
24.1 over many thousands of years, very slowly indeed! For all practical
purposes it is constant.
David H. Levy
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Update: June 2012