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Russian Meteor 15/02/13

February 15, 2013 2 comments

News reports have recently come in of a huge meteor exploding in the air over the Russian cities of Yekatarinburg and Chelyabinsk (about 200km apart), injuring hundreds of people. It’s worth clarifying some of the facts in this matter:

The object that exploded was a meteor, a lump of space rock passing through the Earth’s atmosphere. In this particular case the meteor appears to have exploded around 10km above the ground, over the city of Chelyabinsk.

The shockwave from the explosion damaged some buildings, shattered windows, and set off car alarms. It appears that most of the injuries came from the broken glass, not from the meteor itself hitting anyone.

Showers of fragments from the meteor have been reported too, falling after the explosion over a large area of Russia.

The meteor poses no risk to us any more; it’s all burned up, and it was a one-off random event. Such things are not that rare, happening once every few years, but this one just happened to fall over a populated area.

This meteor was unrelated to asteroid 2012 DA14 that is due to pass by the Earth later today.

UPDATE: A 6m diameter crater has been found in the ice & snow of Lake Chebarkul where the meteorite is thought to have landed:

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The Fireball of 21 September 2012

September 22, 2012 4 comments

Did you see it? Plenty of UK-based stargazers did; a huge, bright, long-lasting fireball streaked through the sky last night, 21 September, at 2255BST (2155UT).


The fireball was caught on meteorlog’s meteor cam

I saw it as I was driving home from a stargazing trip to Loch Tay in the Highlands of Scotland. The first glimpse I caught was behind some trees, and I clearly saw the very bright (estimated magnitude -5), yellow fragments of a space rock that was disintegrating as it burned up in our atmosphere. It was traveling westwards from the SW, and look to be about 40° above the horizon. I lost sight of it as I drove, but once I’d turned a bend in the road, a full ten seconds later, I caught the last few fragments burning it.

Straight away I pulled over and tweeted to see if anyone else had seen in, and very soon a flood of observations came in. The team at the Kielder Observatory actually had a group of people up observing, who all saw it.

Mike Alexander, who runs the Galloway Astronomy Centre, had a group of guests out stargazing then too, and they also saw it, but even better they heard it!

By the time I got home, around 0030BST this morning, only an hour and a half after it happened, there were reports of it on BBC Radio 4, with people all over the northern UK and Ireland reporting the same thing, a disintegrating fireball burning through the night sky for around 20 or 30 seconds.

By the time I woke up this morning it had made it onto BBC News.

So what was it?

A few people suggested that it might have been man-made space debris, an old satellite burning up as it de-orbits, but this isn’t the case, for a couple of reasons. First it was traveling east to west, and satellites don’t orbit in that direction. Secondly, Mike (above) reported hearing a sonic boom approx 150 seconds after it faded. Both of these observations point to the fact that it was a large chunk of space rock, a meteor. When meteors are as bright as this one we call them fireballs.

Fireball of 03 March 2012

Last night, 03 March 2012 at around 2145GMT, my Twitter stream became flooded with reports from people saying they’d seen a giant meteor streaking across the sky.

The first I heard about it was a tweet from @VirtualAstro:

ALERT! Reports coming in of sightings of fireballs (large meteors/ Shooting stars) in the North and South of England

It turns out that these were probably all reporting the same sighting. For a brief spell the hashtag #ukcomet started to gain prominence, but it wasn’t a comet at all, rather a large chunk of space rock burning up in the Earth’s atmosphere.

On any clear dark night you can see a few meteors – which are also known as shooting stars – as the Earth hurtles round the Sun hoovering up all the bits and pieces of debris floating about in space.

Most meteors are the size of a small pebble and as they get hoovered up by the Earth they pass through the atmosphere. This generates frictional heating as the space-rock rubs past air molecules, and eventually the rock will burn up completely. This happens in part of the atmosphere called the mesosphere, which is about 75km (45 miles) above the Earth’s surface. During the brief period of frictional heating not all the energy produced is converted into heat, some of it gets converted into light, which is why we see them streaking across the sky. Usually a meteor will be moving so fast, and burn up so quickly, that is appears as a very quick flash of light, of less then a second in duration.

But there are bigger bits of rock out there too, and when something bigger than around 10cm enters the Earth’s atmosphere we might get a far more spectacular display, something called a fireball, or bolide meteor.

This is what happened last night. Rather than friction heating up the rock (there was probably a bit of that going on too) the energy seen in fireballs is generated by ram pressure. This is as a result of the large rock crashing into the atmosphere and causing all of the air in front of it to rapidly compress, forming a shock wave. The air in this shock wave heats up (did you know that compressed air heats up? Feel the tube on a bicycle pump next time you’re blowing up a tire) and flows around the rock, causing it in turn to heat up. This process starts the rock glowing, and when it’s bright enough we see it as a fireball.

Fireballs are much brighter than standard meteors – in fact the IAU defines a fireball as any meteor brighter than magnitude -4 – and last longer in the sky, and so they’re much easier to spot. Therefore even though they’re much rarer than your common or garden meteors they tend to get spotted by lots more people, and are even visible in big cities, hence the flurry of reports late last night.

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