As darkness falls this weekend, look toward the heavens for a gem of a sky show from one of the year’s best meteor showers, peaking overnight on December 13 and 14.
The annual Geminid meteor shower promises colorful shooting stars and fireballs–but with the moon in the way this year, it’s all a matter of timing, say astronomers.
“The moon is a waxing gibbous around peak and will tend to wash out the fainter objects, but still, the Geminids are one of the top showers, so we can expect a pretty good show,” said Geza Gyuk, astronomer at Adler Planetarium in Chicago.
“And it only takes one spectacular meteor to make the whole shower worthwhile to watch!”
The Geminids are unusual because they’re thought to be the only annual meteor shower created not by a comet but instead by a mysterious asteroid-like object called 3200 Phaethon.
Discovered in 1983 by a NASA satellite, Phaethon is a three-mile-wide space rock. Its year-and-a-half-long orbit precisely matches the appearance of the Geminids, making the body a prime candidate for the source of the meteors.
More detailed recent studies, however, have shown evidence of a debris tail, and the orbit also appears to be very comet-like. The most reasonable interpretation, says Gyuk, is simply that Phaethon is a dormant or inactive comet instead of a rocky asteroid.
“After repeated close passes to the sun, the surface volatiles [frozen gases] have been baked off, leaving a crust of rock that serves to insulate the remaining ices, reducing the outgassing levels,” he said.
Here now is our guide to enjoying this cosmic spectacle:
When is the best time to look up?
The key to planning your Geminid observing session this year will be to keep your eyes adapted to the dark by going out later in the night, when the moon is lower in the sky or has even set. Gyuk suggests sky-watchers position themselves so that a shadow from a thick tree or a building blocks the moon’s direct light.
How many shooting stars will be visible?
Geminids are known for peaking with rates between 60 and 120 shooting stars per hour. The space rocks, which can be as small as a grain of sand or as big as a baseball, hit the atmosphere at around 20 miles per second, creating beautiful, long arcs across the sky. Many last a second or two.
“There is always a possibility of fireballs or even bolides, with the brightest Geminid meteor ever recorded at magnitude -13, nearly as bright as the full moon,” said Raminder Singh Samra, a resident astronomer at the H. R. MacMillan Space Centre in Vancouver, Canada.
“With a bright moon in the sky, even viewing from a dark location in urban skies can be sufficient to see several dozen meteors per hour.”
Where in the sky will the shooting stars appear?
Favoring observers in the Northern Hemisphere, the shower’s radiant—the point in the sky from which the meteors seem to originate—is in the constellation Gemini, which rises above the eastern horizon after 9 p.m. local time. And it’s in the direction of this radiant that some stunning shooting stars can appear.
“Folks should keep an eye out for ‘Earthgrazers,’ these meteors [that] are long and bright that streak from the horizon to overhead,” said Samra.
“They exhibit a long tail as they follow a path parallel to the atmosphere.”
Sky-watchers therefore will want to head outside between 10 p.m. and 5 a.m. local time, with the highest rates of falling meteors in the wee hours of Saturday morning.
How best to enjoy the meteor show?
The best place to catch the Geminids is from a dark site away from city lights with a clear, unobstructed view of the overhead sky. No need for any high-powered views of telescopes or binoculars—the unaided eyes are best since they can soak in the entire sky. Meteors can appear in all parts of the sky.
The only equipment needed: a blanket or reclining lawn chair and some hot chocolate. Stay warm.
For more sky events check out our weekly skywatching column.