Celestia Forums

I was looking at my weather calender for this year, checking out the sunrise/sunset times, and noticed that for my region (Minneapolis, Minnesota), sunrise is at 6:22 am, sunset at 6:21 pm (Central Standard Time), on the seventeenth of march, when the sun doesn't "cross the equator" until march 20. why is there a 3 day difference between the exact 12 hours of daylight, and the vernal equinox?

Refraction.
Atmospheric refraction delays sunset and advances sunrise, so daylight lasts longer than twelve hours on the equinox.