When you wish upon a star...

When you wish upon a star...

You could see a beautiful meteor shower!

What is a shooting star?

The proper name for a shooting star is a meteor. A meteor is a tiny piece of space dust that heats up when it hits the Earth's atmosphere, causing it to glow brightly and creating a shimmering trail of gases. These tiny particles are in orbit around the sun and travel at speeds of 29 to 42 kilometres per second.

Perseid meteor shower_63672main_image_feature_206_jw4

Perseid meteor shower (Image (c) NASA)

When do meteors hit the Earth?

You stand a chance of seeing a meteor at any time of the year as the Earth is struck by about 40 tonnes of cosmic debris per day. The best time to look for meteors is August and November, when the biggest showers of the year  happen: the Perseids (August) and the Leonids (November).

What's with all the ids?

Why are the showers given such strange names? It's all to do with where the meteors appear to come from in the sky. If you look at the photo below, all the meteors seem to come from one point in the sky. This point is called the radiant.

The radiant for the Perseids is in the constellation of Perseus. The radiant for the Leonids is in the constellation of Leo. Get the idea?

So, if you know the name of the shower you have got a pretty good idea of where to look for it in the sky.

Meteor shower - showing radiant

Meteor shower showing radiant

Why do showers happen at certain times of the year?

The Earth goes around the sun in a very nearly circular orbit. Sometimes there are  objects in space that cut across this orbit. Comets often do this. They come hurtling in from the depths of space and their orbits cross the Earth's orbit at the same time every year.

Comets are very scruffy things. The name actually means 'hairy star', and they do indeed moult! They shed millions of tiny particles into the space all around them. These tiny particles follow the same orbit as their comet. Eventually, the particles get spread all around the comet's orbit. This means that every time the Earth's orbit crosses a comet's path, it collides with all the tiny particles and a meteor shower happens.

A NEAT comet_58495main_image_feature_166_jw4

Comet C/2001 Q4 (Image (c) NASA)

Why do all the meteors appear to come from the same spot?

This is actually an optical illusion; the trails just look as if they come from the same spot. It's like looking at a pair of railway lines disappearing into the distance. You know they must be parallel, but your eyes and brain tell you they are getting closer together. This is a 'perspective' effect. Artists use it all the time to make a flat canvas look as if it has depth. The most dramatic demonstration happens if you stand outside in a heavy rain shower and look straight up. What do you see?

Railway lines showing perspective effect

Railway lines showing a perspective effect

Can I become a meteor spotter?

Yes, and the darker the sky, the better. So if you live in the country, great! You can still see them in cities, but you won't see as many. There are always some that are very bright. The Leonids in particular always produce a number of 'fire balls' (very bright meteors). Some even leave a luminous trail that lasts for minutes.

Lie on down (on a blanket or a ground sheet if the ground is wet) and point yourself in the direction of the constellation of the radiant (a star chart helps) and wait. Meteors arrive in a completely random pattern. Sometimes you will see nothing for a while. See how many artificial satellites you spot while you're waiting for the meteors. You may be surprised at how many you can see. They look like steadily moving stars that sometimes get brighter or fade.

Happy star spotting!

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