With the Moon a waning crescent, conditions are very favourable in 2019 for a minor meteor shower that is active in the run-up to Christmas, the Ursids.
Unlike the Geminids, which delivered a fine show earlier in December, the Ursids usually offer only a handful of meteors an hour at their peak. But very occasionally there is significantly enhanced activity.
The period of activity is quoted by the International Meteor Organization as being from the 17th to the 26th of December, with a peak on the night of the 21st/22nd. The IMO suggests patient observers who can sit out and brave the cold may see 5 to 10 Ursids an hour in the pre-dawn hours.
However, in a number of years, there have been outbursts when rates reached 25 meteors per hour for a time. The meteors are produced by dusty debris left by a comet called 8P/Tuttle.
The shower is called the Ursids because the radiant lies in the constellation of Ursa Minor, the Little Bear. This is the northernmost constellation in the heavens, so the radiant is circumpolar from northern latitudes, meaning it is always above the horizon.
You can see meteors at any time when the radiant of a shower is above the horizon. If you live in the northern hemisphere, this means that you get the chance to see them for most of the night, since the radiant is circumpolar, meaning it does not set for most northern latitudes.
However the radiant will be low down in the early part of the night, reducing the numbers of meteors. During the hours before dawn, it rises higher in the sky offering a better opportunity to see some.
From locations in the southern hemisphere, the radiant never rises, so no Ursid meteors can be seen.
As with all meteor showers, the individual “shooting stars” can be seen I any part of the sky. The radiant is the point where the paths of these meteors intersect if you trace them back across the sky. In other words, it marks the direction from which they are arriving from deep space.
Don’t expect a dazzling spectacle, but it will definitely be worth keeping half an eye on the sky, especially as you always have the chance of seeing some meteors unrelated to the Ursid shower too, otherwise known as sporadics, during the night.
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