A pre-Christmas solstice shower that's brief, but bright.
The closest meteor shower to the winter holiday season, the Ursid meteor shower come hot on the heels of the Geminid meteor shower in late December each year.
It's not the most powerful shower of the year, yielding only about 10 shooting stars each hour, but in 2017 it peaks moments after the northern hemisphere's winter solstice. They may be few, but Ursids are brighter than most shooting stars.
So if you are outside at this time of year and you do see a shooting star, it's probably an Ursid.
What are the Ursids?
When you witness a shooting star, what you are looking at is a tiny particle colliding with the Earth's atmosphere, which glows for a split second as it heats up.
These tiny particles of dust and debris are left in the solar system by comets as they pass through on their own orbit of the Sun. The Ursid meteor shower is caused by our planet bumping in to detritus left by Comet 8P/Tuttle, which has been known about since 1790.
Comet Tuttle was last seen in the solar system in 2008, and is due back in 2021.
When can I see the Ursids?
Although officially the Ursid meteor shower stretches from December 17-25, Comet Tuttle leaves a fairly narrow stream of particles. So if you want to see an Ursid meteor you must make sure you view very close to its peak. In 2017, that's on the night of Friday, December 22 and into the early morning of December 23.
The observing conditions this year will be ideal; the new moon is just three days previous, so it will set before midnight. By lucky chance, the northern hemisphere's winter solstice – the exact point when the south pole is tilted toward the sun – will have occurred earlier that day.
Where can I see the Ursids?
Shooting stars from the Ursid meteor shower can appear anywhere in the northern hemisphere's night sky, so you don't have to do anything particularly complicated to see one aside from hunting down a dark country sky free from light pollution.
However, you'll know when you've seen an Ursid because if you trace its direction backwards, it will appear to come from the northern sky; the shooting stars produced by the Ursid meteor shower appear to come from a constellation called Ursa Minor, better known as either the Little Bear or the Little Dipper. It's a much smaller, dimmer constellation than the much more well-known Ursa Major – the Great Bear or the Big Dipper nearby – but there's something else very special about Ursa Minor.
The star at the end of the tale of the Little Dipper is Polaris, which isn't a particularly bright star, but Polaris has a special status among stargazers. It's known as the North Star, because it appears to sit directly above the North Pole, so never shifts. Find Polaris and trace an imaginary line down to the horizon, and you have got the exact point of North.
But how do you find Polaris? That's almost as easy; find the 'pointer stars' Dubhe and Merak on the outer part of the Big Dipper's bowl. The draw a line from Merak (at the bottom of the bowl) through Dubhe, and go five times the distance to the next bright star – that's Polaris.
The Ursids will appear to come from nearby, though actually from closest to the star Kochab nearby in the Little Dipper.
When will the Ursids come back?
Next year's Ursid meteor shower is predicted to peak on the night of Friday, December 21.
However, you should see the Ursids while you can, because in 2018 the Full Moon will be up all night, and its light will blot-out all trace of shooting stars. So brave the cold this Christmas and grab an Ursid while you can.