Our cosmic companion is about to put on its best show of the year
On the night of December 3, sky-watchers around the world will get a chance to revel under the first—and last—full supermoon of the year.
A supermoon is the popular term for a full or new moon that coincides with the lunar orb making an especially close approach to Earth. The moon’s orbit around Earth is not a perfect circle but is somewhat elongated. That means the moon changes its distance to Earth by a few thousand miles over time, reaching a closest point (perigee) and a farthest point (apogee) in any given month.
Technically, this will be the fourth supermoon of the year, but it’s the only one we’ve been able to see with naked eyes. That’s because the other three supermoons of 2017 coincided with new moons, when the lunar disk shows a totally darkened face. (Find out what a “black moon” is and when to see one.)
The December full moon officially occurs at 10:47 a.m. ET (15:47 UT) on the 3rd. Less than a day later, the lunar orb will make its closest approach to Earth for the month, coming within 222,443 miles of our planet at 4:00 a.m. ET (9:00 UT) on the 4th. That means the moon on the night of December 3 will appear about seven percent larger and 16 percent brighter than usual.
Don’t be surprised if you’re having a tough time spotting the difference, though. The moon is so far away, that these subtle changes can be tough to detect with the naked eye.
The best time to enjoy the view will be as the full moon rises just minutes after local sunset, when an optical effect called the moon illusion will make the supermoon appear much bigger and brighter than it will once it’s high in the sky. (Get our tips and trick for how to photograph a supermoon.)
Through the overnight hours, the moon will sit within the bright constellation Taurus, the bull. By covering the lunar disk with your thumb, you can look for the nearby orange star Aldebaran, a stellar giant 65 light-years away that marks the eye of this mythical bovine.
Lucky sky-watchers in northern Alaska, Canada, Russia, and wide parts of China will get to see the moon briefly slide in front of this star.
While there is no need for any special instruments to enjoy the sky show, observers using cameras with telephoto lenses, binoculars, or telescopes can use the opportunity to get enhanced views of the lunar surface.
If your night skies end up cloudy, you can still catch the supermoon online with a free webcast from the Virtual Telescope Project starting at 16:00 UT on December 3. Astronomers will provide real-time images of our beautiful satellite as it rises above the legendary monuments of Rome, Italy.
And don’t worry if you miss this month’s supermoon, because you’ll get two more chances early in 2018. The full moon on January 2 and another on January 31 will also be supermoons.