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They Fall to Earth

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-BOTH: Hello.

-Welcome to the Natural History Museum

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here in London.

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This is the Otumpa meteorite, a piece of space that fell to Earth.

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When I first came here as a small boy I ran through the gallery to try

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and get close to it. I am still impressed today.

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This programme is all about meteorites.

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We've come to see the museum's fantastic collection of space rocks

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and find out what we're still learning about them today.

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We'll bring you the latest on the Chelyabinsk impact in Russia,

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and Jon Culshaw has been on a meteorite hunt of his own in Wiltshire.

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Pete and Paul have tips on what to see in this month's night sky,

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and Chris North has something new - our first Space Surgery.

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Seeing any fireball falling to Earth is very special.

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ALL: Wow!

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What a corker!

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Meteorites are essentially space rocks that are unlucky enough

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to collide with Earth.

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Last month, asteroid 2012 DA14 had a lucky escape, swinging past

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close enough for Sky At Night viewers to capture these amazing images.

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Most meteorites are small

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and the product of a collision between asteroids

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resulting in millions of tiny, rocky fragments which float in space.

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Some get in our way and then burn up in the Earth's atmosphere,

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sometimes creating a fireball and sometimes landing on Earth.

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ALL: Oh!

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But meteorites can come from all sorts of places,

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sometimes from comets and sometimes even from other planets.

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Meteorites are our best way of getting ahold

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of a piece of another world and looking at it close-up.

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The Natural History Museum has one of the finest collections

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anywhere in the world.

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This is just fabulous.

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This is an enormous piece of Mars that fell to Earth in 2011.

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That impact was observed and this is a fresh Martian meteorite,

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kept in this case to keep it away from Earthly contamination.

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That means it can tell us stories of the Red Planet

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and this particular rock is the only Martian meteorite to show

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signs of water, weathering it away in the dim and distant past on Mars.

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These are the latest images from our rovers on Mars

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and their self-portraits show them hard at work

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on the surface of the Red Planet.

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Even though they're doing amazing science, nothing beats getting

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hold of a lump of Mars and bringing it down into the lab.

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700,000 years ago, an impact on Mars resulted in debris

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being flung into space.

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What became the Tissint meteorite wandered through space before falling

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down to Earth, providing us with a hands-on guide to Mars' past.

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At the Natural History Museum, they're using medical CT scanning

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technology to build up an image of Tissint and its insides.

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They're looking for holes or voids inside the rock

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which could be filled with Martian air.

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This is a CT scan of a small fragment of Tissint

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that I looked at last year in the summer.

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'Caroline Smith is the meteorite curator.'

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Just to give you an idea,

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it is about the size of the end of my little finger.

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Quite a small thing.

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What we're seeing here is a video, a movie

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as if we're sort of flying through the specimen.

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'The CT scan has revealed a hole in Tissint which is filled with air.'

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The question is, if this has got air in it,

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is it Earth air or Martian air?

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If it is completely sealed in the rock,

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theoretically it still should have Martian air in it.

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That's what we wanted to find out.

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You can see it is completely sealed at this end.

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Oh, but hang on, we've got all of this red stuff here

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-and in fact, there is a little hole.

-Oh, no!

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Yeah, so if there was any Martian atmosphere in there,

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it ain't there now!

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We wouldn't have been able to do this a few years ago.

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With this, we can get a really good

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idea of what's inside the meteorite without having to chop it up,

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without having to cut it, without having to break it.

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Whenever you do those to any samples, but especially

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rare meteorites, of course,

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you're damaging something rare and precious.

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Meteorites are classified by their composition.

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Some are made of stone, but some are made of iron,

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the condensed cores of what must have been larger asteroids.

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Some are mixtures of both.

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The most interesting meteorites are relics of a time nearly

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five billion years ago, when our solar system was just forming.

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Out of the dust and debris left over from the birth of our sun,

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planets were eventually formed.

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But the details are sketchy and what we need is first-hand evidence.

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We get just that in the form of meteorites

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called carbonaceous chondrites,

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the fossilised remains of the primeval solar system.

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So, we're in the carbonaceous chondrite drawer.

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You can see there's lots of different labels.

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What do they look like? How would we know one if it landed in the back garden?

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They're actually quite boring-looking rocks, actually.

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But that's the thing.

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Their lack of looking interesting belies their significance

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because they're actually some of the most interesting

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meteorites that we actually have to study. This is called Allende.

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Why Allende is very important is primarily because of these things.

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You can see on the surface of this one is this white splodge.

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And then you can see inside as well, there's lots of sort of smaller,

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irregularly shaped white objects.

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These are these things called CAIs,

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stands for calcium aluminium-rich inclusion.

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And the CAIs, we think, are the first solid objects to form

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in our solar system.

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When we talk about the solar system being 4.6 billion years,

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it's actually dating the CAIs

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and in fact, we think in the very, very early solar system,

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in this protoplanetary disc, that's where these rocks

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were beginning to form by bits and pieces all sticking together.

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Another reason why carbonaceous chondrites are particularly

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interesting is because some of them are very rich in organic molecules.

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Right, there is a story about this, isn't there? Is it the Murchison one?

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That's right, the Murchison is one of my favourite meteorites.

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That means it's smelly. That's what I have heard anyway.

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Murchison is smelly.

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Oh, yeah, you get a really strong gunpowder smell out of it.

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It's quite amazing, so I will try...

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And that's been given off by the meteorite?

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This has been given off by the meteorite.

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Now, I will sort of take it out, hopefully no bits will drop off!

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It's quite fragile. So this is a fairly large piece.

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This one weighs about 800 grams.

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You can hold it but very carefully, because it is quite friable.

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And you can see again, a bit like Allende,

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quite a boring-looking meteorite, but it is very, very,

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very rich in organic molecules - amino acids,

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sugars and perhaps the most interesting, I think,

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are nuclear bases, because nuclear bases are the organic molecules

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you need for DNA to replicate.

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I was going to say, these are complicated molecules.

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These are complicated molecules.

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Asteroids and comets carry in them the building blocks of life,

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which then fall to Earth in meteorites.

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They have a sinister presence, emerging from the blackness

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and then disappearing silently again.

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They're dark, cratered worlds, scarred by impacts -

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most ancient, but some quite recent.

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Tracked by telescopes,

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we know precisely where the large ones are,

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but the vast majority of asteroids are too small for us to detect

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until the last minute.

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A fireball is the only sign that something's on the way.

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The last meteorite to fall in the UK was in 1991.

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In that typically understated British way,

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it didn't make much of a fuss

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when it landed in Mr Pettifor's garden, near Cambridge.

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They heard a whistling noise and the neighbour said,

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"Arthur, I think something's just landed in your garden."

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Right at the back of the garden they found this dark rock sitting

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where there had been no dark rock,

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and Mr Pettifor was clever enough to realise that this was

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something quite unusual and maybe this was a meteorite.

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You get lots of these calls

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from people who think they've found meteorites.

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A few hundred a year, yes!

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So when you go out to chase one of these up -

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the story sounds convincing - but what do you look for in the rock?

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The first thing that's very characteristic

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is the very, very dark crust.

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-Burnt is the wrong word...

-Well, it's melted rock.

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It's called the fusion crust, so as this meteorite was hurtling through

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Earth's atmosphere,

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the rock actually melts, but only on the outside.

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The inside never gets hot enough to melt.

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I'm going to give away a little secret here.

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One of the ways that we filter calls when people say,

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"A meteorite landed in my garden last night,"

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we always say to them, "What happened? Was it hot when you picked it up?"

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As soon as they say, "Yes, it was boiling hot,"

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or, "It set the grass on fire," or whatever,

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then it's not a meteorite

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because the very few occasions, I should say,

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where meteorites have landed and somebody has picked them up

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almost immediately afterwards, they are described as being "lukewarm."

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Well, this is the last British meteorite,

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but of course, we've had the Russian meteorite in Chelyabinsk, which was very exciting.

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What do we know about that?

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The best guesstimate at the moment for the size of the object

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when it came into the Earth's atmosphere

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is about 17 metres wide.

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What sort of percentage survives to the ground?

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Well, it's difficult to say,

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but you might lose at least half the pre-atmospheric mass and size...

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Thousands of stones have already been recovered

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and the largest one, I think, is about two kilograms.

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Is there scientific value in getting it so soon after an impact?

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Oh, absolutely.

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The less time a meteorite is sitting around on the ground for,

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the less it is being contaminated.

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More than 1,000 meteorites fall to Earth every year.

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Caroline regularly goes meteorite hunting in the desert,

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where conditions are ideal for preserving them.

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In 2010 in Australia, she found a funny little rock,

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which at first glance, looked nothing special.

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Lucy is meeting up with Anton Kearsley

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in the basement of the museum.

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He used his electron microscope to look at Caroline's find

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and was amazed at what he found.

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It was something incredibly rare - a meteorite from the moon.

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This is an image of a cutaway of the meteorite,

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-magnified by a certain number of times.

-That's right.

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On the screen at the moment, it is about 300 times magnification.

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On the picture over here,

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you can see that the whole thing is just over a centimetre in size.

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It's about a fingernail size.

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And this is a really curious little area.

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Because there's a little dark grey patch

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with some little pale grey patches inside it.

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And when you start analysing the pale grey patches,

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these ones turn out to have a very interesting chemical composition.

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It turns out to be quite unlike the composition of things

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-that we find on Earth.

-OK.

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This is a little mineral again, silicate mineral

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but now it's got a lot of very strange elements in it.

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It's got zirconium, and yttrium

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and titanium and iron and silicon,

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it's actually quite well-known,

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but it's called tranquillityite.

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The Mare Tranquillitatis -

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one of the most famous features on the moon

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and where man first stood.

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These precious meteorites give us

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clues about the moon's ancient past and how it's changed,

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which is why finding them in pristine condition is so important.

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On Earth, deserts hot and cold

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are ideal for preserving these extraterrestrial rocks.

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The Antarctic has become the new Mecca for meteorite hunters.

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Since 1976, ANSMET,

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the US Antarctic Search for Meteorites program

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has retrieved 20,000 meteorites.

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Lunar scientist Katie Joy spent two months in Antarctica

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and her group managed to collect 63 meteorites,

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but they were hampered by the wind

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and temperatures of -25 degrees centigrade.

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Katie returned in January

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and to remind her of her Antarctic experiences

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we took her to a bar in central London made completely of ice

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and it was a balmy -5 degrees centigrade.

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It's only -5 in here, it was -25 in Antarctica! This is easy!

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So, Katie, why go to the extreme of visiting Antarctica

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-to look for your meteorites?

-Antarctica's a desert.

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It has very little rainfall and precipitation,

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which means that the meteorites that are found there

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are very well preserved.

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Also there are no trees, no buildings...

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It's easy to find a nice big black meteorite sitting on the white ice,

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so it's kind of an easy thing to do.

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This is a good example of the dark meteorites

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that would be sitting on the ice.

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Are there particularly good places to look for meteorites on Antarctica?

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There are.

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Meteorites fall randomly all over Antarctica as they do the rest of the world,

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but what happens is that the ice on the polar plateau

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flows out towards the edge of the continent

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and when it hits the mountain ranges,

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the ice is brought up to the surface

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and so we find natural concentration sites,

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typically along the big mountain ranges,

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such as the Transantarctic Mountains.

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It's cold enough being in here,

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working in Antarctica

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must have been incredibly challenging. Tell me about your experience.

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I was there for six weeks on the ice, a very remote area,

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and every day we'd get up and if the weather was good enough

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we would go out and search.

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Sometimes if you have a lot of snow or it's very windy -

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Antarctica's completely unpredictable -

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you get stuck in the tent which is frustrating,

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cos all you want to do is go out and find more meteorites.

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It's hard work, but when you find them, it's a great award.

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Antarctica is still a rich source of meteorites

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with more science visits planned in the future.

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Every meteorite, it seems, has a story of its own.

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This is the largest meteorite in the museum's collection from Cranborne

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in Australia and at three-and-a-half tons,

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it weighs the same as four cars.

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It's an impressive beast and it is older than the Earth.

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But, we have some impressive meteorites in Britain too

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and Jon has been on the trail of one of them.

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This one may have been carried along by a glazier and it even

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attracted the interest of prehistoric man,

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but it was rediscovered sitting on someone's doorstep.

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This is the Iron Age hill fort at Barbury Castle near Swindon,

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first occupied some 2,500 years ago.

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And what a wonderfully atmospheric and peaceful place this is.

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There's a real air of mystery around here.

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And all around you can see the remnants of the influence

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of ancient man - this Iron Age fort, burial mounds, and it brings to mind

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those stories of those Victorian amateur archaeologists who used

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to love to explore and dig things up and whatever they found fascinating

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or just liked the look of, they would take home to their collections.

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This old photograph from Country Life in 1908 is of the Lake House mansion

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in Wiltshire, once owned by the Rev Edward Duke.

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He was known to excavate local burial grounds,

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keeping any interesting pieces for his own private collection.

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On the doorstep is certainly something very interesting.

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It's the Lake House meteorite.

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Here at the Salisbury and South Wiltshire Museum,

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I met up with Professor Colin Pillinger.

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'He's become a meteorite detective and he's been piecing together

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'the history of the Lake House meteorite.'

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-Ah! There it is. The Lake House meteorite.

-Indeed. You can't miss it.

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-It's a fair size, isn't it?

-Well,

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-it is 92.5 kilograms.

-Wow!

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But this is not only the BIGGEST British meteorite that we

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know about, it is also the one that has been longest on Earth

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and it was when we made that measurement that all of us

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suddenly realised we had something quite exciting.

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So how old exactly is this meteorite

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and how long has it been on the Earth?

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It's technically 4.5, 4.6 billion years old.

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It's been on Earth 32,000 years

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but to try and explain how it survived 32,000 years,

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you have to tease some facts out of it.

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32,000 years ago on Salisbury Plain,

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the place was covered in ice.

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We're confident that we know meteorites survive very well in ice,

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because we collect lots of meteorites on Antarctica.

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How do you explain the next bit?

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Bronze Age people living on Salisbury Plain,

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sort of 4,000 years ago

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were building mounds to bury their important people.

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The meteorite was then put into one of these barrows.

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The majority of the rock that they used would have been chalk.

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You've these lovely pictures of the meteorite on the step, you see

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the patches of chalk still on the meteorite,

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so it clearly was packed somewhere closely associated with chalk.

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Colin believes that after it was dug up, the meteorite must have

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been kept inside, protected in Edward Duke's collection.

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But after his death, it was demoted to the doorstep,

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possibly used for kicking off mud from gentlemen's boots.

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Since then the chalk has washed off and you look at the meteorite now

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and there's no chalk there.

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So it can't have been out on that step for more than about 100 years.

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So the story goes, 32,000 years ago, a meteorite fell in Britain

0:19:090:19:15

and was preserved in a glacier.

0:19:150:19:17

Then, used by Bronze Age man to build his burial mound

0:19:170:19:21

and dug up by a Victorian archaeologist.

0:19:210:19:24

Using a series of clues, Colin has revealed an extraordinary tale

0:19:240:19:28

about an extraordinary meteorite.

0:19:280:19:31

A wonderful piece of serendipity.

0:19:320:19:35

-The needle left the haystack and made its way to you.

-Absolutely.

0:19:350:19:38

Science is a lot of serendipity.

0:19:380:19:41

Such good fun.

0:19:410:19:43

We hope that serendipity will play a part tonight.

0:19:470:19:51

We're back at Barbury Castle to look for comet Panstarrs,

0:19:560:20:00

which we hope to see in a couple of hours.

0:20:000:20:03

Pete, Paul and Chris North are here too.

0:20:030:20:07

The sky is fairly clear and we're hopeful.

0:20:070:20:11

But this comet is low down and very faint.

0:20:110:20:14

We're joined by the Wiltshire Astronomical Society

0:20:140:20:16

to look for it and last night,

0:20:160:20:18

member Pete Glastonbury saw the comet

0:20:180:20:20

and what a bonny comet it is too!

0:20:200:20:23

Let's hope we'll be as lucky tonight.

0:20:230:20:25

We're waiting for the darkness to fall

0:20:290:20:32

and when we first arrived, it was awful, wasn't it?

0:20:320:20:35

-It was and it has cleared, I have to say.

-It has.

-Extremely lucky.

0:20:350:20:39

This is rare on a Sky At Night shoot!

0:20:390:20:41

We are also joined by some of our beginner astronomers...

0:20:410:20:45

Peta and Steve Bosley and Christina Chester.

0:20:450:20:48

They've come to pick up some tips about observing Saturn,

0:20:480:20:52

which is in our April night sky...

0:20:520:20:55

Rising around 10pm at the beginning of the month

0:20:550:20:58

and getting earlier as the month goes on.

0:20:580:21:01

-Have you ever seen Saturn through your telescope?

-No, just Jupiter.

0:21:010:21:04

Well, you are in for a real treat with Saturn because it's a stunner.

0:21:040:21:08

That's the planet which actually hooked me into astronomy.

0:21:080:21:11

-How do you find Saturn?

-OK, well, you know what The Plough looks like?

0:21:110:21:16

-Yep.

-You know the handle of The Plough?

0:21:160:21:19

If you follow the curve of that away from the blade bit,

0:21:190:21:23

if you like, or if you carry on the curve round,

0:21:230:21:26

it comes to Spica -

0:21:260:21:27

the brightest star in Virgo,

0:21:270:21:29

and Saturn is off

0:21:290:21:30

to the lower left of Spica

0:21:300:21:32

and it's about the same brightness.

0:21:320:21:33

-D'you reckon we're going to see the comet tonight?

-Fingers crossed.

0:21:340:21:37

I can't see your fingers crossed in those gloves, but I'll trust you.

0:21:370:21:41

So, the reason why Saturn is so good to look at in April

0:21:420:21:46

is because it's at opposition and when a planet is at opposition,

0:21:460:21:49

then this is the best time to look at it.

0:21:490:21:51

We thought we'd do a little demonstration to demonstrate the opposition.

0:21:510:21:56

You are going to be the sun. Peta, you'll be the sun.

0:21:560:21:59

Steve, you can be the Earth. Can I ask you to stand here, please?

0:21:590:22:02

-Of course.

-There we are, you are the planet Earth.

0:22:020:22:06

I shall represent Saturn, a ringless Saturn. So this is opposition.

0:22:060:22:12

It is when the sun and the planet in question

0:22:120:22:15

are at opposite sides of the Earth.

0:22:150:22:17

We have the sun in one part of the sky

0:22:170:22:20

and in the opposite direction of the sky we have the planet Saturn.

0:22:200:22:23

How many moons does Saturn...?

0:22:250:22:27

It's got loads of moons,

0:22:270:22:28

but most of them are too faint to be seen with a small telescope.

0:22:280:22:32

But there is a good family of them that go around the planet itself.

0:22:320:22:36

More than you would see with Jupiter.

0:22:360:22:38

They are always in attendance

0:22:380:22:40

and they are really worth

0:22:400:22:41

looking out for as well.

0:22:410:22:43

JON: The darkness and the cold is enveloping us

0:22:480:22:52

but this Iron Age fort feels really quite magical.

0:22:520:22:56

OK, we've got Neil and Hillary here and you're locals?

0:22:580:23:02

-Yes, we're from Devizes.

-Have you had any luck finding the comet?

0:23:020:23:05

No, so we're hopeful that we'll see it tonight.

0:23:050:23:08

I think we're all hopeful. Kids, what do you guys get out of it?

0:23:080:23:11

-I like planets and space stations and stuff!

-Planets are good.

0:23:110:23:15

I like seeing all the galaxies and the stars and things.

0:23:150:23:18

I think the comet is currently hiding in a bank of cloud

0:23:200:23:25

and comets are really delicate things in the night sky

0:23:250:23:28

so when you get any haze, particularly in a bright sky

0:23:280:23:30

like we've got now, it just washes them out completely.

0:23:300:23:33

It's like a comet filter!

0:23:330:23:36

JON: While we wait in hope for the stubborn clouds to

0:23:360:23:40

clear from the horizon, it is time for our Space Surgery.

0:23:400:23:45

Now, the first in a new feature on the Sky At Night.

0:23:450:23:48

It is our Space Surgery, where we shall do our very best to

0:23:480:23:52

answer the astronomical questions that you may have.

0:23:520:23:55

Our first question comes from Mary Pont of Cambridgeshire

0:23:550:24:00

and she lives in a bungalow, quite low down.

0:24:000:24:03

She's not got a telescope, just her own eyes

0:24:030:24:06

and a pair of 750 binoculars. So is there anything that she can look for?

0:24:060:24:11

The best thing to do, Mary, is to find your way around the rest

0:24:110:24:14

of the sky, so get yourself a night sky guide, perhaps.

0:24:140:24:17

Mary's binoculars aren't too dissimilar to the ones

0:24:170:24:19

I am holding here.

0:24:190:24:20

They're great for hunting for star clusters

0:24:200:24:23

and there are a few examples of that.

0:24:230:24:25

One of the ones with a chart on our website is the M44,

0:24:250:24:27

the Beehive Cluster or Praesepe.

0:24:270:24:29

It's a really great place to start,

0:24:290:24:31

and looks fabulous in a pair of binoculars like these.

0:24:310:24:35

This next question is a great one and I used to wonder this

0:24:350:24:37

when I was a lad.

0:24:370:24:39

Why are planets, stars and moons perfectly round

0:24:390:24:42

and are there any that are not?

0:24:420:24:44

So asks Lawrence from Eccles.

0:24:440:24:47

It's a very good question

0:24:470:24:49

and the answer quite simply is gravity, so once a rocky object

0:24:490:24:52

which is what planets, moons and asteroids are made of,

0:24:520:24:55

gets more than a few hundred kilometres across in diameter,

0:24:550:24:59

then its own self gravity, its own gravitational pull,

0:24:590:25:02

its own mass, pulls everything into pretty much a round sphere.

0:25:020:25:06

A great example is some of Saturn's moons,

0:25:060:25:08

the bigger moons such as Rhea, Titan and Enceladus

0:25:080:25:11

are nice, round bodies but some of the smaller ones such as Prometheus

0:25:110:25:15

and Pandora are much more odd shapes

0:25:150:25:17

because they're too small for gravity to have pulled them.

0:25:170:25:21

The next question is from another Chris, Chris Fordham in Huddersfield.

0:25:220:25:26

As our galaxy is so vast, is there a simple way to tell

0:25:260:25:30

when looking at stars if they are outside our Milky Way?

0:25:300:25:35

The simple answer is that all the stars you can see

0:25:350:25:38

are our inside our own galaxy.

0:25:380:25:39

Measuring distance to objects in astronomy has always been a challenge.

0:25:390:25:43

There are various ways of doing it and there was a result out

0:25:430:25:46

that we've just measured the distance to one of the nearest galaxies,

0:25:460:25:49

the Large Magellanic Cloud through knowing the properties

0:25:490:25:53

of those stars in the galaxy themselves

0:25:530:25:55

and by determining those, we've measured the distance to that

0:25:550:25:57

of 163,000 light years to within an accuracy of one part in 50.

0:25:570:26:03

So we are getting much better at measuring distances to stars in other galaxies,

0:26:030:26:07

but it is actually something that in astronomy is very hard to do.

0:26:070:26:11

If you have a question, we'll do our best to answer it,

0:26:110:26:14

so send it to us at...

0:26:140:26:16

Well, we didn't actually get to see the comet in the end,

0:26:240:26:26

-did we, chaps?

-No, we didn't.

-But not to worry.

0:26:260:26:28

We have a beautiful, clear night here.

0:26:280:26:30

It's not the last chance to find it, right?

0:26:300:26:32

No. Comet C2011 L4 Panstarrs

0:26:320:26:35

will be in our skies for some time yet.

0:26:350:26:39

It's getting fainter as time goes on,

0:26:390:26:42

but throughout the month of April,

0:26:420:26:44

it'll pass up through Andromeda, through Cassiopeia toward Cepheus.

0:26:440:26:49

And it actually goes quite close to the Andromeda galaxy as well.

0:26:490:26:53

A good opportunity to pick out the comet still throughout

0:26:530:26:56

the month of April.

0:26:560:26:58

Sadly it eluded us.

0:26:580:27:00

That bank of cloud was like two pub bouncers saying you're not coming in!

0:27:000:27:05

We may have been unlucky, but not so for many of you.

0:27:080:27:12

Our Flickr site has some amazing images of the comets

0:27:120:27:15

from around the world.

0:27:150:27:17

You can see the best of them on our website at bbc.co.uk/skyatnight.

0:27:170:27:23

We have one more celestial treat.

0:27:370:27:40

Lucy and Chris have been allowed

0:27:400:27:42

to hold something rather precious.

0:27:420:27:44

Well, this is something really special.

0:27:470:27:50

This is a piece of Martian meteorite and so this little rock

0:27:500:27:53

knew Mars when it was a wet world, travelled out into space

0:27:530:27:57

and then ended up here on Earth, where it can tell us its story.

0:27:570:28:01

I'm holding the piece of the moon that Anton showed me earlier on.

0:28:010:28:03

Trapped in this tiny fragment is the history of the lunar surface

0:28:030:28:07

from that area.

0:28:070:28:09

A huge thank you to the Natural History Museum for showing us

0:28:090:28:12

behind the scenes and allowing us to hold these very special objects.

0:28:120:28:15

When we come back next month, we'll be going past the moon,

0:28:150:28:19

past Mars and on out to Saturn.

0:28:190:28:21

So, until next month...

0:28:210:28:22

-BOTH:

-Good night.

0:28:220:28:24

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