The Geminids and the son of the Sun

This is annual meteor shower is one of the most reliably strong. It will be at its peak in the night of December 13/14.

See the end note about enlarging illustrations.

Most meteor showers consist of fragments shed from comets, but the Geminids derive from a 6-kilometer-wide asteroid, 3200 Phaethon, which has a very short orbit of only 1.52 years and goes nearer to the Sun than any other named asteroid. Hence its name, from Phaethon, who persuaded his father Helios to let him for one day drive the chariot of the sun across the sky. Unable to control the mighty horses, he let them career too near and then to far from Earth, thus scorching the Aethiopians (the “burnt-face” people) and freezing the Arctic, and Zeus had to kill him with a thunderbolt.

Maybe I’ll make that lurid scene into my cover painting for Astronomical Calendar 2023, after the style of the fall of Icarus (1997) or Europa and the bull (2005), though it will be an online book like the new Astronomical Calendar 2022.

I find the rendering of the fall of Phaethon by Rubens too complex, and it doesn’t show the tropics being scorched.

The Geminids, deriving from an asteroid rather than a comet, must include rock-sized pieces, which as they burn up in the atmosphere are often bright and do not leave trails.  Following approximately the asteroid’s orbit, they cross inward close over Earth’s orbit almost sideways – from only slightly to the front, and slightly to the north.  They appear to come at us from near Castor in the constellation of the twins, and from this “radiant” point their paths streak to any part of the sky.  The radiant is up for almost all of the long (northern) winter night, highest at 2 AM.

In this view from ecliptic north, the broad arrow shows Earth’s flight along its orbit in 3 minutes, and an arrow on its equator shows its rotation in 3 hours.  America is coming around into a view of the Geminid radiant higher in the sky.

At the time and place of our horizon scene, the radiant has just risen into view.  It will keep climbing (parallel to the celestial equator) as the long night goes on.

The ZHR, or zenithal hourly rate, of the Geminids is given as 120; this is what an alert observer might count under ideal conditions if the radiant were overhead.  Actual rates are liable to be less.  This is arguably the best shower of the year – it does not produce wild storms like the Leonids, but since about 1960 it is said to have superseded the famous Perseids of August as the most reliable.

This year, the Moon, two days past its first-quarter phase (and far less than half as bright as when full), is about a quarter of the way around the sky ahead (west of) the Geminids’ radiant. So it is in the sky when the Geminid radiant rises, but will set around 2 AM.

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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format.  You may be able to enlarge them on your monitor.  One way: right-click, and choose “View image”, then enlarge.  Or choose “Copy image”, then put it on your desktop, then open it.  On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers).  Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.

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