Geminids are much slower than either the summer Perseids or the hit-or-miss Leonids, because they don’t strike us head-on; they come at Earth sideways. At 20 miles per second, they lope along at half the speed of the other major showers, and it shows. It’s very appealing. Instead of sharp, brief zaps across the sky, we get leisurely streakers.
Geminids are abundant from midnight to dawn. If you were to pick a single half-hour “window” to watch, I’d say to start at 2 a.m. A sky-ruining Half Moon (with bright Jupiter next to it) sets around 12:30, so serious meteor-lovers should go out after that time – even though some Geminids will be seen as early as 9 p.m. Or, if you’re already an early riser, head out at 5 or 5:30 a.m., but no later. Then you’ll also get to see dazzling Venus in the east.
These meteors are the most mysterious in the known universe. All other showers are debris from comets: skimpy stuff, chunks of ice. Strangely, Geminid meteors are twice as dense. What could they be?
There are other oddities, too. All other major meteor showers have been observed for centuries or millennia. But the Geminids were unseen as recently as the mid-1800s, when they started as a modest shower that delivered only 20 meteors per hour. Over time they’ve grown increasingly rich; now they deliver one to two a minute – often the year’s best display.
Despite decades of searching, the source of these strange fireworks was unknown until 1983, when NASA’s infrared-detecting satellite found a small body moving in exactly the same path as the meteoroid swarm. Named 3200 Phaethon, it has a speedy, oval, 1.4-year orbit that carries it far within the orbit of Mercury, and then out past Mars into the asteroid belt. Since Phaethon does not develop a cometlike tail nor shed material when approaching the Sun, it was assumed to be an asteroid – a rocky body.
Fine. Except asteroids don’t disintegrate to produce meteor showers: curioser and curioser. Nowadays a few researchers continue to believe that Phaethon is nonetheless a true asteroid that suffered enough collisions to fill its lopsided orbit with debris – which means that it’s asteroid-stuff that we observe on December 13. But most astronomers now think that Phaethon is an odd, unique, has-been comet – one that completely lost its outer covering and is at present just a comet-core that has perhaps acquired a coating of interplanetary dust grains. Either way, the mystery material puts on quite a show.
Try to get away from lights, to a place with an open expanse of sky. Bring a folding chair to be comfortable, or else stand there taking in as much sky as possible. In the middle of December, lingering outdoors after midnight is odd behavior – like mixing tuna fish with marshmallows, the way my sister does.
Be patient, keep your eyes glued upward, and if it’s clear Monday night you will see meteors. Count on it.