Return of the Orionids

Meteors from the annual Orionid shower may be seen sparsely for much of October. If you see a bright streak that can be traced back to their “radiant,” near the upraised club of Orion, it is an Orionid, rather than a sporadic bit of space dust.

The Orionids have a broad peak of about a week, say Oct. 19 to 25, over which there is probably little difference. The theoretical peak moment this year is Oct. 22 at 0h Universal Time, which may be when Earth passes closest to the center of the meteor stream.

The Moon reaches its first quarter position early on Oct. 22, so in the evening hours it is shining over in the west of the sky. The best hours for glimpsing the meteors will be after midnight.

The Orionid radiant climbing into view. See the end note about enlarging illustrations.

These meteors are fragments from Halley’s Comet. See our page about this, with a 3-D view of the orbit: https://www.universalworkshop.com/halley-meteors/

The Orionids are Halley meteors on the way in, crossing north of the October part of Earth’s orbit; and the Eta Aquarids are Halley meteors on the way out, crossing south of the May part of our orbit. But the distance between the orbits is greater on the inward leg, so that we encounter an outer part of the stream; the Orionids are less abundant and can hardly count as a major shower. The ZHR, or zenithal hourly rate, is estimated as 50 for the Eta Aquarids and 20 for the Orionids. This is the average number a single alert observer might expect to see if the radiant is exactly overhead and if sky conditions are perfect – neither of which is likely to be true. So, dress warmly, take a look after midnight, you may be lucky enough to see the fiery end of a small piece of the great comet that thrilled us in 1986 and will next whip through the inner solar system in 2134.

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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” or “Open image in new tab”, 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.