Bob Moler's Ephemeris Blog

This is Ephemeris for Monday, December 9th. Today the Sun will be up for 8 hours and 53 minutes, setting at 5:02, and it will rise tomorrow at 8:09. The Moon, 1 day past first quarter, will set at 2:20 tomorrow morning.

Today is the date of the earliest sunset, in the middle of a 13-day stretch where the Sun sets within the same minute. We are still 12 days from the winter solstice, the day of the shortest daylight hours, on the 21st. The reason is twofold. The Sun is approaching its farthest position south of the equator, where the longitude lines are closer together, so it takes less time to cross them. 15 degrees in longitude equals one hour in Earth’s rotation. Add to that we are less than a month from Earth’s perihelion in its orbit of the Sun, that is at its closest, and is moving faster than average. The combined effects delay sunrise and sunset, from what they’d be if the Sun stayed on the equator and the Earth’s orbit was circular. We will have our latest sunrise on January 2nd.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.

Addendum