Rain isn’t the only thing that falls in large amounts in December. This month, multiple swarms of hot little rocks will also shower.
Fortunately, meteors rarely hit the ground. (And when they do, they immediately acquire a different label: meteorites.)
For cosmically coincidental reasons, this month happens to be packed with meteor showers. Nobody’s making any promises about Pacific Northwest weather, but if skies are clear, night owls might spot whole squadrons of incoming projectiles from beyond.
That’s guaranteed to take patience, so bundle up and find a wide-open spot where you can linger. Like bird-watching, shooting-star-watching tends to be a matter of waiting for something to happen while hoping you’re pointed in the right direction.
Meteors last only moments, but they’re worth waiting for. Few naked-eye sky-watching phenomena are as spectacular and satisfying as catching a long arc of light swooping across the sky. Short lines or wriggles are more common, but they’ll still make you gasp.
Meteors are space rocks — lumps of iron and other minerals — that literally burn up as they drop into Earth’s atmosphere. There’s nothing rare about this. Random shooting stars are spotted daily, as wandering space detritus finds its way here after asteroid collisions or other cosmic violence shakes it loose.
But when meteor activity isn’t random at all — when many meteors stream from one region of the sky — that’s a shower. Meteor showers occur when the Earth passes into the cluttered path of a comet.
Comets are frozen bundles of rock and gas that follow irregular orbits through super-cold deep space. (Astronomers sometimes call them dirty snowballs.) When they approach the sun’s warmer neighborhood, they start melting and growing tails of detritus that streams out behind them. That detritus — some of it boulder-sized, but much microscopic — spreads out over time but keeps following the same orbit around the sun.
When the Earth’s orbit brings it through that messy zone, we get to enjoy an annual light show. The light trails of meteors are the signature of heat caused by friction in the atmosphere. Meteors are fragile and usually tiny, and rarely survive the plunge. While 48.5 tons of meteor material hits the atmosphere daily, less than 5 percent of that ever reaches the ground, according to NASA.
Meteors that do make it are usually pebble-to-fist sized. It can be hard to distinguish meteoric rocks, but their dark-glazed surfaces stand out in desert and polar regions, according to NASA. Surviving evidence of really huge meteor strikes is rare on Earth, with just 190 confirmed impact craters listed in a clearinghouse called the Earth Impact Database.
One immense crater that’s buried under the Gulf of Mexico and Yucatan peninsula is evidence of the biggest meteor strike in all of Earth’s prehistory. An asteroid as large as 9 miles wide smacked the Earth there 66 million years ago, tossing tons of debris into the atmosphere, blocking the sun and triggering a lengthy “impact winter” that radically cooled the entire planet.
While scientists disagree whether that asteroid came from a comet or some other source, there’s little disagreement about the catastrophic outcome: a rapid mass extinction that wiped out three-quarters of all life on Earth, including the dinosaurs.
How to watch
As they follow specific orbits through space, meteors seem, to our eyes, to emerge from regions of the sky associated with specific constellations. That’s how they get their names. For example, the Geminid shower — one of the major annual showers beloved by skywatchers — seems to radiate out from the constellation Gemini.
While many meteor showers require patience, you can increase your odds of seeing lots of them by going someplace very dark. Reflected light from a nearly full moon may present a significant challenge early in the month, but the moon’s phase will wane as the weeks go by. And, moonrise will shift from early to late evening and then into the wee hours of morning.
Unfortunately for people with bedtimes, that’s when many meteor showers are known to peak — in the wee-est of hours, nearer to dawn — so the later and darker you can make it, the better. Serious skywatchers who stay up very late or get up very early can sometimes be rewarded with dozens, or even hundreds, of visible meteors per hour.