The Geminids get their name from the constellation of Gemini, the twins. During the overnight hours of Thursday to Friday, the night of this shower's maximum, the meteors will appear to emanate from a spot in the sky near the bright star Castor in Gemini.
But how unfortunate that the Geminids are relegated to December, when nights get very cold across much of the United States. While August's Perseids get the most attention, because they appear on balmy summer nights when many people are on vacation, knowledgeable skywatchers know that the "cold Geminids" almost always surpass the Perseids. So, if you are willing to brave a long lookout of possible-subfreezing temperatures, you will be amply rewarded. [Geminid Meteor Shower 2018: When, Where & How to See It]
Bright ... and faint
In studies of past Geminid displays, these meteors scored high marks for both quality and quantity. The Perseids or Leonids seem to whiz across your line of sight in a second or less, but the Geminids are noticeably slower. I've often said they resemble "celestial field mice" as they scurry across the sky, producing good numbers of bright, graceful, yellowish-white meteors and fireballs. The Geminids also include many dim meteors, with surprisingly fewer shower members of medium brightness. In other words the meteors you'll see will be either quite bright or rather faint.
The Geminids typically encounter Earth at around 22 miles (35 kilometers) per second. That's about half the speed of a Leonid meteor. And only about 2 to 4 percent of all Geminids leave a persistent train in their wake. That's probably due to their composition: At 2 grams per cubic centimeter (1.15 oz per cubic inch) on average, Geminid meteoroids (the term for meteors before they hit the atmosphere) are several times denser than the cometary bits of fine dust that make up most meteor showers.
This may be because of their origin: They seem to have come not from a comet but from 3200 Phaethon, an Earth-crossing asteroid. Then again, the Geminids may be comet debris after all; some astronomers think Phaethon is the dead nucleus of a burned-out comet that somehow got trapped into an unusually tight orbit.
According to Margaret Campbell-Brown and Peter Brown in the 2018 "Observer's Handbook" of the Royal Astronomical Society of Canada, peak activity for the Geminids this year is projected to occur at or near 7 a.m. EST (1200 GMT) on Dec. 14. That timing strongly favors North America.
Under normal conditions on the night of maximum activity, from midnight to 4 a.m. local time with ideal dark-sky conditions, an average of at least 60 to 120 Geminid meteors should burst across the sky each hour. (Light pollution will greatly cut down on the numbers, however.) The best time for Geminid viewing will come at 2 a.m., when the constellation Gemini will stand almost directly overhead. (Note that the times in this paragraph refer to your local time zone, wherever you're watching from.)
The Geminids perform superbly in most years. However, as was the case for last month's Leonids, the moon will pose a small hindrance. It will reach first-quarter phase on Dec. 15, the day after the Geminid peak. On the evening of Thursday, Dec. 13, the moon will shine brightly in the dim constellation of Aquarius, the water carrier. That means that moonlight could wash out some of the fainter Geminids. However, the moon will set by around 10:30 p.m. local time on Thursday, leaving the sky dark and moonless for the balance of the night and making for perfect viewing conditions.
Slow rise ... and rapid decline
The Earth moves quickly through this meteor stream.
Two nights before the peak, hourly rates average one-quarter peak strength. On the night before the peak, about half as many Geminids appear as compared to the night of maximum. After maximum, the numbers drop off sharply. The night after the peak, the shower is once again down to about one-quarter peak strength, and two nights after the peak, only a handful of residual stragglers will remain.
Another interesting fact is that the meteors seen right up to the night of the peak are generally faint, but after the peak, the preponderance of visible meteors are especially bright.
I alluded to this earlier, but I will remind you once again: This time of year, meteor watching can be a long, cold business. You may be lying down on a long lawn chair or snuggled up in a sleeping bag waiting to catch sight of a meteor. If they don't appear right away, and if you're cold and uncomfortable, I suppose you're not going to look for meteors for very long!
Don't expect meteors to appear at equally spaced intervals of, say, 1 per minute. Instead, you'll probably experience what some have called the "clumping effect." You may see a sudden burst of activity, followed by a lull of several minutes or more.
Therefore, make sure you make yourself warm and comfortable. Hot cocoa, tea or coffee can take the edge off the chill, while also providing a slight stimulus (but avoid alcoholic beverages). It's even better if you can watch the shower with friends. That way, you can keep each other awake, as well as cover more sky.
A few more tips: Look up for as wide a view of the sky as possible. Perhaps listen to some music as you watch. Lastly, give your eyes time to dark-adapt before you look — and good luck!
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications, and he is an on-camera meteorologist for Verizon FiOS1 News in New York's lower Hudson Valley. Follow us on Twitter @Spacedotcom and on Facebook. Original article on Space.com.