Sky-gazers have one more big night to get excited about before 2018 comes to a close. On Friday, December 21, a cold moon and the Ursid meteor shower fall on the longest night of the year, presenting a rare, end-of-the-year treat for astronomy fanatics.
The Ursids appear in the night sky every year around December 17 through the 26. The shower is on the tamer side, peaking at five to 10 meteors per hour in a typical year, but it's been known to spike unexpectedly with as many as 100 meteors flaring in an single hour.
This year, the peak night of the shower coincides with two big celestial events. Friday, December 21 marks the winter solstice—the time when the Northern Hemisphere is tilted farthest from the Sun, giving us the shortest day and the longest night of the year. It's also the night of a cold moon. A cold moon is a regular full moon that appears during December. Like a strawberry moon, the first full moon of summer; and a harvest moon, the first full moon of autumn, the name refers to a certain time of year rather than anything special going on with the celestial body.
A cold moon hasn't fallen within 24 hours of winter solstice since 2010, and it won't happen again until 2029. Though it makes for an exciting trifecta, the full cold moon will unfortunately make the Ursids harder to spot the night of December 21 and the morning of the 22nd. If you don't catch them at their peak tonight and tomorrow, the shower is expected to continue into next week.