Hi vwroom,

It's the solstice (http://en.wikipedia.org/wiki/Solstice) - days get longer in the summer and shorter in the winter for the northern hemisphere and vice versa for the southern hemisphere.

Hope this helps!

cjd
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The Rate of change would follow the graph of a sine wave where the top and bottom crest and trough are the Solstice and the rate of change would swap from positive to negative or vice versa. Therefore the maximum rate of change would occur at the equinox.
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The days get longer faster near the solstice, rather than the equinox. You can look at http://www.laalmanac.com/weather/we88b.htm for the sunrise/sunset times in Los Angeles this year.

Look at January (closer to the winter equinox). From January 1-10, the sunrise goes from 6:59 to 7:00am. The sunset goes from 4:55 to 5:02am. January 1, the day (hours:minutes) is 9:56 long. January 10, the day is 10:02 long, a difference of 6 minutes in 10 days.

Now look at March 16-25 (with the solstice right in the middle of that range). Sunrise/sunset on the 16th is 7:02am/7:03pm. On the 25th, it's 6:50am/7:09pm. The day is 12:01 long on the 16th, and 12:19 long on the 25th, a difference of 18 minutes over those 10 days.

Doing the math, the days near the solstice get longer three times as fast as they do near the equinox. Hope that helps.
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Solstice isn't it?
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