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Ephemeris: 12/12/2023 – The source of the Geminid meteor shower

December 12, 2023

This is Bob Moler with Ephemeris for Tuesday, December 12th. Today the Sun will be up for 8 hours and 51 minutes, setting at 5:02, and it will rise tomorrow at 8:11. The Moon is new today, and won’t be visible.

The Geminid meteor shower, which will peak this Thursday, is caused by a small body called 3200 Phaethon which looks like an asteroid but has the orbit of a comet, coming close to the Sun and back out to the asteroid belt. It’s probably a dead comet, with all the volatiles sublimated away leaving only the rocky bits. It is named Phaethon, because at the time it was the asteroid that came closest to the Sun. In Greek mythology Phaethon, the son of Helios the Sun god borrowed his father’s chariot that carried the Sun to take it out for a spin one day with disastrous results. The Geminid meteor shower was first recognized in 1862. The hourly rates of the Geminids have increased every year since then. The meteor stream has completely filled in the orbit of Phaethon, and they’re being pushed around by the gravitational effect of the planets and the pressure of sunlight.

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

3200 Phaethon showing a tail
3200 Phaethon a rock comet showing a tail as it nears the Sun. Credit NASA/STEREO
Time-lapse radar images of Phaethon from Arecibo.
The orbit of 3200 Phaethon
Orbit of 3200 Phaethon with the orbits of the planets from Mercury to Jupiter. Credit TheSkyLive.com.
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