While the Orionid Meteor Shower continues tonight, I wanted to take some time to explain and breakdown a few things baout meteor showers that will hopefully add some context to what you may see while you look up in the night sky.
A meteor shower is when the earth passes through a bunch of left over debris in outer space during the Earth’s orbit around the sun. Take a look at this very sophisticated graphic:
Since there are other things (mainly comets and asteroids) also traveling around the Sun in orbits that cross the Earth’s, when the earth traverses the orbit of that other celestial body, we also pass through the debris left behind.
As that debris enters earth’s atmosphere it is rendered aglow as that debris heats up as it descends toward the ground. It heats up, expels all of its gas, forms a little streak in the sky and then poof! Often, the debris is so small that it bursts before reaching lower in the atmosphere.
Why is there debris?
Often asteroids and comets are not “whole” pieces but rather multiple chunks of stuff packed together by gravity.
For comets, as they round the sun, the heat of the sun melts, sublimes, and breaks apart some of the ice that is holding some of it together. This allows chunks of the comet that are not ice to break apart and drift away. The tail of the comet is the gas being expelled as the sun heats the comet. In fact “Comet” comes from the latin word “Coma” meaning “hair of the head” because the tail of the comet looks like hair.
For asteroids, these can break apart for many reasons. Sometimes gravity tugs at little chunks as the asteroid rounds its own orbit, other times they collide with other asteroids. And in other cases, ice is helping to hold the chunks of asteroid together and once the ice is gone, the asteroid isn’t held together as strongly. And chunks of it can drift away.
In either case, once debris is dislodged, it may not travel as the same speed around the sun as the asteroid or comet is moving. As it slows down, it forms a trail of debris.
And because these asteroids and comets have been around for thousands, millions, and – in some cases – billions of years, the trail of debris can get pretty long.
When can I see one?
You can see a meteor shower whenever the Earth moves through one of these trails of debris. It isn’t a singular event. Often times meteor showers last a few nights. This is because as the asteroid or comet has been in orbit, the orbit isn’t always perfect. There is a little wobble. Sometimes it is a bit further away from the Sun, other times it is a bit closer to the Sun. This creates a field of trailing debris that the Earth must get across while the Earth orbits the Sun.
Keep in mind that the Earth is moving in its orbit at about 18 miles per second. So the fact that these meteor showers last a few days means that the “field” of debris we are traveling through is a few thousand miles across.
The best plan is to get away from city lights, and get to a place with fewer trees, and look up.
While there is a best time to look, any time when it is dark will allow you to see “shooting stars.”
The other cool factoid here is that this is also happening during the day! There are “shooting stars” flying around with the same density during the day, but we can’t see them because the sun is brighter than the streaks of light.
How often does this happen?
Pretty often! There are many orbits of comets and asteroids that the Earth plows through during the year.
A brief meteor shower calendar:
Lyrids – April
eta Aquariids – May
Perseids – July – August
Orionids – October – November
Leonids – November
Geminids – Early December
Ursids – Late December
Now enjoy your next meteor shower!
Now that you know what causes them and how they work, you can rest easy knowing you can enjoy a meteor shower any time the earth passes through one of these fields of debris
