What causes meteor showers

¡SkyCaramba! Weekly astronomy blog for the week ending May 31, 2014

When dust particles and space rocks collide with Earth’s atmosphere at thousands of miles per hour, they heat up. Military satellites designed to detect heat trails from missiles also see these bits of stuff from space traveling through our atmosphere. If the meteors are hot enough, they glow and we can see them with our own eyes. We call them meteors.

Meteors are quite often yellow or white, but they can also be green, red, or blue. It depends what the dust is made of and how hot it glows.

Much of the stuff that strikes the atmosphere is about as big as a grain of sand. Astronomers frequently refer to all of it as dust, although some of it is too big to be adequately described that way. Some debris is as big as parking lot gravel. Some items are as big as baseballs. The most spectacular meteors are burning rocks even bigger. They could be bigger than a house.

You can see meteors any night if the sky’s clear. There’s plenty of haphazardly strewn stuff out there for Earth’s air to sweep up any time on our planet’s way around the sun. But on some nights, you can see a meteor shower. That’s when our planet passes through a dust trail left behind by a comet.

A comet passed in front of Earth's path and led to speculation that there would be a new meteor shower in May 2014

Meteor showers are fairly regular as far as when they occur. Since our calendar is tied very closely to Earth’s position in orbit, the planet passes through the same area again on or close to the same date. But it’s hard to predict just how many meteors will be seen. A shower that’s strong one year can be weak the next. And when scientists successfully predict a strong shower one year, they may be wrong about it the very next year.

These showers are hard to predict because it’s so hard to tell just how much dust is coming off a comet at any given time. The dust also disperses in ways that aren’t well understood as it drifts in space. Add to this the fact that a comet is shedding dust in or close to its older dust trails. And even when the comet is in a stable orbit, its orbit is subtly changing as the dust it loses takes energy with it.

Meteor showers are named for the constellations the meteors appear to radiate from. The visible parts of their trails don’t always start there, but they can be traced back. So the Geminids trace back to Gemini. And the Camelopardalids, a new meteor shower that was expected to happen on May 24, 2014, would trace back to Camelopardalis.

Follow the links below to learn more about meteor showers. ¡SkyCaramba!