Each December, the Earth passes through the dusty trail of the asteroid 3200 Phaethon, resulting in a spectacular meteor shower known as the Geminids. This year’s cosmic display will peak on the night of December 13 and into the early hours of December 14. You won’t want to miss it; the Geminids are shaping up to be the best meteor shower of 2018.
As Joe Rao explains on Space.com, the Geminids are relatively slow-moving meteors. They typically enter Earth's atmosphere at about 22 miles per second, about half the speed of the Leonid meteors, which soar through the darkness each November. This in turn means that the Geminids take a longer time to travel across the night sky, making them easier to spot. In perfect conditions—which is to say under clear skies and away from light pollution—you might be able to see as many as 120 Geminid meteors per hour during peak activity.
Like other meteor showers, the Geminids happen when extra-terrestrial debris hits the Earth’s outer atmosphere and heats up, ultimately disintegrating into fiery bursts of color, according to NASA. But unlike most meteor showers, which originate from icy comets, the Geminids stem from the mysterious rocky object 3200 Phaethon. Scientists aren’t entirely sure how to classify 3200 Phaethon; it has many characteristics of an asteroid, but boasts the elliptical orbit of a comet. Some astronomers refer to 3200 Phaethon as a “rock comet,” essentially an asteroid that gets very close to the sun, resulting in a scorched trail of debris that might lead to meteor showers on Earth.
Though they originate from 3200 Phaethon, the Geminids appear to radiate from the constellation Gemini—hence the shower’s name. The Geminids will be visible starting from about 9 or 10 p.m. on the night of December 13, but the American Meteor Society says the best time to see them will be between 1:00 and 2:00 a.m. local time on the 14th. That’s because, from our vantage point on the ground, the meteors seem to move more quickly as the Earth turns towards Gemini; during the earlier hours of the night, the meteors will appear longer and more sluggish. Moonlight also threatens to outshine some of the dimmer Geminids, but the moon is due to set by about 10:30 p.m. local time on the night of the shower, leaving the sky dark and clear.
Locations far removed from tall buildings and light pollution are best for Geminid gazing. Matthew Cappucci of the Washington Post recommends not looking directly at the Gemini constellation, which in this context is known as the shower’s “radiant,” because you’ll see only quick flashes of light. To catch the meteors’ colorful tails in all their glory, it’s best to take a wide view of the sky.
The shower favors the northern hemisphere; in the southern hemisphere, the meteors’ radiant point rises later, and is above the horizon for a relatively short period of time. At this time of year, many northerly regions are quite cold, so be sure to pack warm clothes, blankets and hot drinks. Then lie back and enjoy as the Geminids light up the night sky.