The Geminids and where they come from

The particles that make the Geminid meteor stream come in across the December part of Earth’s orbit like this.

See the end note about enlarging illustrations.

Rather than being debris from a comet, as with most meteor streams, they have are pieces from an asteroid, 3200 Phaethon, which has a very short orbit.  One of the things this accounts for is that many Geminids are bright, being large solid chunks.

The meteors come at us from somwwhat north of the ecliptic plane, and roughly sideways, rather than from ahead like the Leonids, so they hit our atmosphere with medium speed and are visible most of the night instead of only after midnight.

This time, unfavorably, the Moon is shining from almost he same direction, because it is near Full – outward from Earth.

In this space picture, Earth is seen from ecliptic north (the north pole of its orbit).  The broad flat arrow shows its flight along its orbit in 3 minutes, and the arrow on its equator shows its rotation in 3 hours.  The actual stream of particles in space is millions of miles wide; the dotted line represents only those that happen to arrive from exactly overhead.

America at this time is moving toward midnight, when the Geminid radiant – and the Moon – will be highest.

Compare last year’s Geminid night.

– when the Moon was well out of the way.

You’ve already seen this morning ‘s pictur of this evening’s scene, but here it is again.

The radiant is the place in the sky to which meteor trail can be traced back – if they lie in some other direction they are sporadic metoers, not Geminids.  Radiants shift slightly from day to day during the shower’s days or weeks of acitivity, as expressed by the arrow through the radiant point.  Each hour, the sky turns as indicated by the arrow on the celestial.  By midnight, the Geminid radiant will be about at its highest – and so will the Moon.

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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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