When You Wish Upon A Star

Asides from being useful for bringing inanimate puppets with a propensity for fibbing to life, shooting stars are also rather exciting to watch. This is just as well because we are about to hit the peak for the Perseid meteor shower. But what actually is a shooting star? Hale-Bopp; Swift-Tuttle; Halley's, these are all comets and comets all have something in common. Comets are effectively giant, dirty snowballs and as they sail around the solar system bits of water ice and rock and other debris stream off behind them, this is especially the case as thy warm up when they pass near to the sun. This cometary debris just sort of hangs about in the vacuum of space until an unwitting planet like ours happens to come piling through it.

A shooting star, then, is actually a tiny piece of comet that is entering our atmosphere and burning up as it does so due to the extreme heat produced as it drags through the air. The Perseid meteor shower is called such because the debris from the comet all appears to be entering the sky around about the constellation of Perseus. People much more clever and talented than I are able to take multiple images of Perseid meteors and overlay them, these combined images make it much more obvious what I mean when I say they radiate out of the Perseus constellation; see below.

Keeping the Greek theme going, comets are so called because back in the day the Greeks thought of the streaming tail of a comet as flowing long hair. Their word for that is κομᾶν which morphed into Κομήτης their word for comet, which my Greek buddy Anastasia reliably informs me is pronounced komiti.

The comet Swift-Tuttle, which I mentioned above, is actually quite pertinent here. It is the tail debris of this comet that we pass through every August which gives us the Perseid meteor shower, a phenomenon that astronomers have been observing for over two thousand years now. I was wondering if the meteor shower would diminish in magnitude each year as we slowly but surely clear the area of debris as we keep going through it, but then it gets replenished once Swift-Tuttle hurtles through every 133 years. I've struggled to find any information on this so I've tweeted a couple of proper astronomers to try to find out. I'll update this post if they get back to me.

In the meantime, if you're in the UK, look to the northeast in the evening and get some wishes ready.

**UPDATE: Astrophotographer extraordinaire and Sky At Night presenter Pete Lawrence got back to me about my theory and I'm totally wrong. The earth hardly removes any of the debris compared to how much the comet sheds and it does indeed replenish it as it orbits so, if anything, perhaps the Perseids will get more intense with time.**

Image courtesy of NASA