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Ephemeris: 12/21/2023 – Winter comes late this evening

December 21, 2023 Comments off

This is Bob Moler with Ephemeris for Thursday, December 21st. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:04, and it will rise tomorrow at 8:17. The Moon, 2 days past first quarter, will set at 3:37 tomorrow morning.

Today is mostly the last day of Fall, since the moment of solstice will arrive at 10:28 pm (03:28 on the 22nd UTC). If you’re south of the equator this is the first day of summer. The Earth reaches a point in its orbit where its North Pole is tipped its furthest away from the Sun, and is in shadow in the middle of its six-month night. The Sun for us is up only 8 hours, 48 minutes, and to boot the Sun only rises 22 degrees above the horizon giving us the least amount of energy of any day of the year. Why did the ancients celebrate this time of year? That’s because the Sun had slowed and stopped its drift southward and was beginning to come back higher in the sky. Spring and summer would eventually return!

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –5 hours). They may be different for your location.

Addendum

Solstices
Comparing the sun’s path at the summer and winter solstices for Traverse City, MI Latitude ~45 N. This is a stereographic representation of the whole sky which distorts the sky and magnifies the size of the sun’s path near the horizon.
December solstice
The Earth and its axis on the first day of winter, the winter solstice. From my Sun and the Earth talk slides.
The Earth near December solstice
Not quite the solstice, this is the Earth on December 16th, 2015 taken by the EPIC camera on the DISCOVR spacecraft at the Sun-Earth L1 point, some 1 million miles (1.5 million km) sunward from the Earth. The South Pole is in the middle of its six-month day, and the North Pole is in the middle of its six-month night.

Categories: Concepts, Earth, Ephemeris Program, Seasons Tags: