When skywatchers think of meteor showers during the month of December, they immediately think of the Geminids, which over the years have evolved into the most prolific and reliable of the dozen or so annual meteor displays that take place. And yet, there is also another notable meteor shower that occurs during December that, in contrast, hardly gets much notice at all: the December Ursids. The peak of this meteor display usually occurs on the night of Dec. 22 to Dec. 23.
While the Ursids would normally be difficult to see during this time because of bright light from the full moon, the rare upcoming total lunar eclipse may provide a special chance to catch a glimpse of the Ursid meteor shower.
Check this NASA lunar eclipse chart to see how visible the eclipse will be from different regions around the world.
The Ursids are so named because they appear to fan out from the vicinity of the bright orange star Kochab, in the constellation of Ursa Minor, the Little Bear. Kochab is the brighter of the two outer stars in the bowl of the Little Dipper (the other being Pherkad), that seem to march in a circle like sentries around Polaris, the North Star. These meteors are sometimes called the Umids, in a rather unsuccessful attempt to make clear that they originate from the direction of Ursa Minor, not Ursa Major.
The fact that Kochab is positioned so near to the north pole of the sky means that it almost never sets for most viewers in the Northern Hemisphere.
And since the Ursids seem to fan out from this particular region of the sky, you can look for these faint, medium-speed meteors all through the night if you care to. The fact that they reach their peak on Dec. 22 to Dec. 23, however, is not good news for prospective Ursid watchers in 2010, as this coincides with the first full night of winter, with a brilliant nearly full moon that will shine in the sky all night from about 5:00 p.m. local time onward.
This is unfortunate because the underappreciated Ursids "badly need observing," according to the British Astronomical Association.
That observers have neglected the Ursids is not surprising. Everything about them is wintry.
The Ursid meteor shower usually coincides with the winter solstice, and is best seen by polar bears since they come from near the celestial north pole. In contrast to the Geminids, which can produce up to 120 meteors per hour, the usual Ursid rate is but a fraction of that; generally speaking they produce about a dozen or so per hour at their peak.
The Ursids are actually the dusty debris shed by the periodic comet Tuttle 8P/Tuttle, which circles the sun in a 13.6-year orbit and was last seen in early 2008. On occasion, the Earth has interacted with a dense, narrow stream of particles shed by this comet, which has caused brief outbursts of Ursid meteors numbering in the dozens per hour, but no such interaction is expected this year.
The eclipse will help!
But don't cross the Ursids off your observing calendar just yet. As I noted above, this year they coincide with a brilliant almost-full moon, which likely will squelch visibility of most meteors. If only the moon weren't in the sky...
But wait! The night before the Ursid peak (Dec. 20 to Dec. 21) is the long-awaited total eclipse of the moon. In fact, for 72 minutes, while the moon is completely immersed in the Earth's shadow, the moon will appear anywhere from 10,000 to 100,000 times dimmer and will allow many of the fainter stars and even the Milky Way to temporarily appear. [Amazing photos of a total lunar eclipse]
And possibly a few Ursid meteors too! Usually not many people would be outside on a cold late-December night looking up at the sky, but the eclipse will be the feature attraction that will draw many outdoors.
So if, while you're admiring the totally eclipsed moon, you happen to also catch sight of a few meteors streaking from out of the northern part of the sky, congratulations! You've probably caught sight of the Ursids.