Astro Bob: Here come the Geminids! Best meteor shower of year
The annual Geminid meteor shower, best of the year, peaks on Sunday night, Dec. 13-14, with dozens of meteors visible per hour.
I hope you can set aside an hour or two for a scintillating show this weekend. The annual Geminid meteor shower is active through the first day of winter but peaks on Sunday night, Dec. 13. From a dark, moonless sky more than 100 meteors per hour might be visible. However, since most of us have to deal with varying amounts of light pollution we're more likely to see closer to 50-60 an hour from outer suburban areas. Still more than enough for an enjoyable experience.
Whether you stay at home or travel to dark skies wear your warmest clothes and bring a folding lounge-style chair. If you watch standing up you'll get a kink in your neck. Better to stretch out on your back under a thick blanket or sleeping bag for a relaxing view of the sky overhead. And don't forget the hot chocolate ... and marshmallows.
Meteor-shower watching is one of the best ways to enjoy the sky. All you need are your eyes and for clouds to remain at bay. It's also a wonderful family activity or socially distanced way to get together with friends. You're outdoors, and it's easy to spread out. As a bonus, the Geminids are active during both evening and early morning hours, so you don't necessarily have to drag yourself out of bed at 2 a.m. like you would for other showers.
The name "Geminids" comes from "Gemini the twins" because the meteors all shoot out of a small patch of sky called the "radiant" near the constellation's second brightest star, Castor. Geminids can flash anywhere — east, west, south north, overhead. But you'll know it's a shower member and not a random meteor if you can trace the path back to Gemini.
The radiant is a perspective effect similar to looking down parallel railroad tracks that appear to converge in the distance. Like rails, meteors travel on parallel paths through the atmosphere. They only appear to converge because we're looking upstream into the distance as the Earth plows forward in its orbit. You'll see the same radiant effect when driving at night through a snow or rain storm. Meteors (or snowflakes) close to the radiant make short, little dashes while those further away form long streaks.
To sample both short and long-trailed meteors, it's best to look about 45 degrees to one side of the radiant. For the Geminids that means you can face north or southeast during evening hours. After midnight, when the constellation is much higher in the sky, face south or southwest.
You can start meteor-watching as early as 9 p.m. local time because the radiant will already be 30 degrees high or a third the way up the sky. I suggest spending at least an hour with the shower for a satisfying and immersive experience. Lucky for evening viewers, the Geminids reach their pinnacle around 7 p.m. CST, helping to offset the smaller number of meteors typically visible when the radiant is still relatively low.
As Gemini and the radiant climb higher, especially in the early morning hours, meteors have the complete run of the sky without getting cut off by the horizon. That will significantly boost how many you see. Also, after midnight, the part of Earth you're living on turns into the direction of the planet's motion around the sun, so you head directly into the meteoroid stream. Prior to midnight, meteoroids have to catch up with the Earth. Using another snowstorm analogy, it's the difference between driving into an approaching storm versus driving away from it.
You'll spot a modest number of meteors around 9 or 10 p.m. Or you can loose a little sleep and observe between 1 a.m. and 5 to see more. I like to split the difference and sample both temporal realms by starting around 10 and finishing up at 12:30 a.m. Sometimes I'll set a goal of say, 30 meteors, but I almost always exceed that because the sense of anticipation proves too seductive. Each needle of light convinces me to stick around for the next until minutes become hours.
Meteor showers are funny. At times you might see one flash a minute, followed by a 4- or 5-minute pause when everything seems to come to a dead stop. Then all of the sudden two meteors will blast into view simultaneously, and the action starts anew. The Geminid shower is richer in Venus-bright meteors called fireballs than any other. Yet another reason not to miss the show. Nor will the moon interfere this year and steal away the fainter meteors. We won't get another moonless Geminid show until 2023.
Of course there's all the other cool stuff you experience when you're out under the stars. Occasional satellites, random meteors, the sound of owls and coyotes and of course the grand entry of Orion and his entourage of brilliant suns.
So where do these meteors come from? Most meteor showers originate from dust released by icy comets when they're heated by the sun. But the Geminids are something of an oddity. The stem from an asteroid named 3200 Phaethon (FAY-uh-thon), which dips closer to the sun than any other asteroid known. At closest approach (just 13 million miles or 21 million km) its surface heats up to 1,300 degrees Fahrenheit (700 degrees Celsius), hot enough to stress the rock and make it crack and crumble.
The bits and pieces, collectively called meteoroids, spread out along Phaethon's orbit. Every mid-December the Earth crosses the path of debris laid down by the asteroid, and the material strikes the atmosphere at 22 miles per second (35 km/sec). That's so fast that each tiny fragment glows hotly and excites the air molecules around it to glow, too. Together, they create the streaks of celestial fire we're willing to stay up late for.
2020 has been a difficult year for mind and body, but the sky continues to be a place we can go to find calm and experience wonder. Our sense of amazement never disappears, you know. Just gets buried under the leaves sometimes.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob .