Tuesday, 13 August 2013

The sky is falling!

So, I've got this Cousin, right, and he's an Astronomer (Safety Tip: they REALLY don't like being called Astrologers - Not even by accident, I mean, I've seen one spontaneously combust under these conditions, it's not pretty - You don't want to do it if you're wearing your best clothes.)  He's not a full-time Astronomer, obviously... I mean, he doesn't do it during the day, and I'm reliably informed that not many of them do, what with the whole lack of visible stars thing, and that pesky sun causing the teensiest bit of light pollution.

Anywho, he was on Aleena Naylor's breakfast show on BBC Radio Derby this morning talking about the meteor shower that we're currently all experiencing - Trying to calm the populace, convincing them that the sky was not falling and that no, sacrificing a chicken or Edward Woodward wouldn't help the situation in any way, shape or form.

So, what are these strange lights in the sky?  Are they dangerous? Should we wear a hat when we go out? Are they different from that huge killer fireball that threatened to vapourise Russia in February?

Well, unless you've been living (or more likely cowering, shivering, rocking backwards and forwards, crying a bit) under a rock for the past week, you'll know that they're called the Perseids.  But why are they called that?  Well, mainly because they 'appear' to come from the direction of the constellation of Perseus (Which you will find just under the much easier to identify 'W' shaped constellation of Cassiopea, in the sky, mostly at night).  Does this mean that aliens in that constellation are shooting rocks at us?

Yes, yes it does probably - We should all run and hide... But not for a couple of thousand years yet, and I'll talk about that later.

Put simply, all the wonderful lights you may, or may not see when you look up into the night sky are dust, usually smaller than a grain of sand, travelling at anywhere between 25 and 160 THOUSAND miles an hour (That's between 33 and 210 times the speed of sound kids) and they would come really keen if they hit you on the back of your leg - You'd have a bruise for days.  Luckily, the vast proportion of them disintegrate as they burn up in the atmosphere.

But why is space full of dust? and has this anything to do with the popular mouth-exploding treat 'Space Dust'?  I'll answer the second question first... No... No it doesn't.  One is a mixture of boiled sugar and pressurised CO2 and the other is the excreta from a comet.  In the case of the Perseids, this is the fallout from comet Swift-Tuttle, a charming ball of ice and rock that swings round our part of the solar system every one hundred and thirty-three years.  This particular snowball however is sixteen miles across (About the size of Birmingham) and weighs (OK, has a mass of - before the Science nerds all gang up, gaffer tape me to a hobby rocket and launch me into a tree) about eight quadrillion metric tonnes (That's an eight with fifteen zeroes after it - give or take a zero - My degree's not in maths)

Every time our new friendly little galactic icepop goes near the sun, it melts a little (as you would) and bits fall off, most of that is ice, but enough of it is dust and pebbles to leave a trail around our solar system.  Every July/August the Earth goes through this trail and we get peppered by it, thus causing the lightshow - Simple as.

Do these space-dusty-rocky things ever not burn up and go on to bullseye a cow (possibly in Venezuela, maybe in 1972) and kill it instantly by blasting it in half?  Well, yes, technically that does happen.  But you shouldn't worry as it's incredibly unlikely - In fact, a chap called John S. Lewis, Author of the book 'Comet and asteroid impact hazards on a populated Earth'  (who probably had nothing to do with the Department store) once said 'No one in recorded history has ever been killed by a meteorite in the presence of a Meteoricist and a medical Doctor' - But, in fairness, I've been alive for forty-five years (as of last Saturday.. Where was your card?) and I've never knowingly done anything in the presence of both a Meteoricist and a medical Doctor, so that doesn't really mean a lot.

Did you notice something there?  The chances of one of these things surviving to impact the Earth is so slight that they get a new name:

Meteor - space-dust that burns up in the atmosphere

Meteorite - scalding hot death rock that survives its trip through the atmosphere, turns cows into spaghetti sauce and causes light bruising to people called Hodges, in Alabama, when they crash through their ceilings and bounce off their radios.

Anne Hodges, 60 years ago, with her space-ouchie

Back to Russia... It was difficult to turn on the TV in February and not see the beginning of that Bruce Willis film about the Earth-Killing comet impact... Thing is, it was actually real-life footage of a real-life event.

Big badda-boom!

This was obviously a Meteor (see above) but it didn't actually start life as part of a comet, it was one of the Apollo Asteroids that we share an orbit with around the Sun (In fact, there's a massive cloud of them that fills the space between us and the Sun, we're constantly swimming through this cloud - Doesn't that make you feel better?) and it was 'Only' about 20 meters across, but still weighed more than the Eiffel Tower and was travelling at about forty two THOUSAND MPH (or a mere sixty times the speed of sound)  It didn't hit the ground in one piece, luckily, but exploded about fourteen miles up in the air with a blast calculated to be about 20-30 times more powerful than the Hiroshima nuclear explosion.  This caused hundreds of small meteorites to hit the ground, disappear into snowdrifts, melt holes in ice-covered lakes and ruin a couple of perfectly serviceable fur hats.  The sound from the explosion was so loud that the echoes took more than a day to die down - You probably heard it without even realising... And you thought Brian Blessed was loud?

Very, very rare though, things like this.  So rare in fact that we had a near miss from another, bigger, asteroid on the same day, only we were so busy watching the first one, that we missed it.  It passed us at a distance of 17,000 miles (To give you some idea of how close that is, the Moon is 250,000 miles away - or fourteen times further) and it was half as big again as the one that lit up Russia - It is the largest thing that we know has ever passed that close to us without wiping out any dinosaurs.

And finally, remember where I said that we should worry a bit, but not for a couple of thousand years?

Well, it seems, that our friendly, neighborhood comet, Swift-Tuttle, mother of the Perseids, crosses the orbit of the Earth again on, or about Sept 15th. 4479 - two and a half thousand years in the future - No one we know will be alive then, the chances are that us Earthlings will have scattered ourselves across the Solar System by then, either by colonisation or as radioactive dust and it'll be close, about ten times as far away as the moon.

Everything should be fine... as long as, in the next 2,500 years, nothing effects its orbit at all, even by a minuscule amount, say 1,000 miles a year (which, in celestial mechanics terms is 'the square root of bugger all') - Because then it will hit the Earth square-on.

It will be travelling at 134 THOUSAND miles per hour and it's getting on for three times the size of the one that's supposed to have taken out the dinosaurs.

Should be quite impressive, as long as you're watching it from a distance.  Sleep tight dear readers, and keep watching the skies.

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