The Geminids: A Fiery Death


(Photo, via Wikipedia: "Leonid Meteor Storm, as seen over North America in the night of November 12./13., 1833. Source, E. Weiß: "Bilderatlas der Sternenwelt"; Published 1888)

The Earth is hurtling through mostly empty space at nearly 70,000 mph. But space is only mostly empty. Throughout the solar system is debris left behind by comets, colliding asteroids, and even dust from interstellar space. When the Earth hits these things – at 70,000 mph – it puts on a nice show.

You can see the show any time of the year. Just find a dark moonless sky and stare up for a while. You'll eventually see the quick streak of a shooting star. That "shooting star" was what happens when one of these tiny dust-sized pieces of debris gets in the way of the earth. It burns high in the atmosphere. Very very occasionally the earth will run into an even larger piece of debris.

The best I ever saw in my life was when I was sitting on a beach in Hawaii and noticed a bright light behind me, turned around, and saw a huge bolide split multiple times in the air before disappearing behind a volcano behind me.

These days they are often caught by security cameras or by whoever happens to have a video camera in their hand at the time.

Some parts of the solar system are dirtier than others, and right now the Earth is plowing through one of the dirtier ones. We are plowing right through the orbit of a former comet, and that orbit is full of dust and small rocks sputtered out by the comet over centuries. The comet has lost so much debris, in fact, that by now it appears as a barely distinguishable rocky asteroid quietly orbiting the sun.

If you want to see shooting stars and see a lot of them, now is a good time to get outside and do it.

When? Where?

There's a little bit of bad news here, that you can understand just by thinking about how the direction Earth is moving through space. View from the north pole, the Earth goes counter-clockwise around the sun. So imagine, as we did a few days ago, that you are looking down on the Earth and that the Sun is off at the 6 o'clock position. If you were standing on the Earth at the 6 o'clock position the sun would be straight overhead; it would be noon. If you were standing on the Earth at the 12 o'clock position it would be the middle of the night: midnight. Since the Earth also rotates counter clockwise, if you are standing at the 3 o'clock position you see the Sun on the horizon, but soon you will rotate into darkness: sunset. And at the 9 o'clock position you will be experiencing sunrise. The 9 o'clock position is also special because it points in the direction that the Earth is travelling around the sun. In other words, if you are standing on the Earth and the sun is rising and you point straight up (and you don't live too close to the north or south pole!) you will be pointing in the direction that the Earth is travelling.

The Earth is slamming into the cometary debris as it travels, so the place to look is in the direction of travel. Straight up. Sunrise. Sunrise is, of course, too bright, so you're actually better in the hours before sunrise when it is still dark. The Moon and Jupiter will have set (don't miss Venus and Saturn, too, but we'll talk about those next week), and the skies will be dark. (The debris itself is moving too, actually, so this rotates the impact point around enough that the actual best time is more like 2am, but any time after the Moon sets and before the Sun rises should be fabulous).

What will you see? No one ever knows precisely what a meteor shower will show, or even precisely when it will peak. The current one is expected to be good tonight, better tomorrow night, and fade quickly. At its peak you could see a shooting star every minute from a nice dark clear site. If you're lucky, you'll see one split into pieces and color the skies.

It's the end of life for the little piece of cometary debris that first coagulated out of the interstellar cloud of gas and dust more than four billion years ago. It's been a long ride: billions of years out in the asteroid belt, finally heated and ejected from a comet, a lonely flight through empty space, and then a firey death as the Earth slams into it. Don't you want to be there to see its last ride?