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I would like to tell you what we know about this event and give you an idea of what to
expect in the future perhaps. So, let's get started. First of all, some terms. You can't
have a talk without defining things, at least not in my field. Meteoroid, meteor, meteorite
what's the difference? Well there is a difference though people use them interchangeably a lot.
A meteoroid is a chunk of rock or ice out in space. It's about the size of a boulder
or smaller. Now some people ask, "What's the difference between a meteoroid and an asteroid?"
It's all a question of size. There is no dividing line. So, some people would say a rock, a
meter across, a yard and a half across is an asteroid. Others would say it's got to
be about 10 meters or 10 yards across before it's an asteroid. I prefer thinking something
bigger than a garage which is 10 yards, is an asteroid. Something the size of a beach
ball, that doesn't strike me as an asteroid, I would call that a meteoroid. So that's the
difference. It's a question of size. But you will get a different answer depending on which
scientist you talk to. So, I'm giving you my opinion. There is no formal definition.
Now, when that chunk of rock and ice out in space hits our atmosphere it burns up, it
ablates because they hit the atmosphere pretty fast. Most meteors move anywhere from 40 to
170,000 miles per hour, many times faster than the space shuttle hitting the atmosphere.
So when they hit, they burn up, they leave that streak of light that you see as a shooting
star, or a falling star. That streak of light is what we call a meteor. So the meteor is
not the rock or the ice itself, it's the streak of light it produces when it burns up in the
atmosphere. And finally, any piece of that meteoroid that makes it to the ground, we
call it a meteorite. So a meteorite is something that has actually made it to the ground. And
yes, the moon and Mars have meteorites on them too so it's not specific to the Earth.
So any piece of a meteoroid that survives atmospheric ablation and makes it to the ground
is called a meteorite. Any questions on that? So, Luther now knows the difference here.
He got whacked by a meteorite. Now when it comes to meteors there's a thing
called a fireball, which is a bright meteor. Technically, a fireball is a meteor brighter
than the planet Venus. That's a fireball. And a superbolide is something that's really
bright. It will cast shadows on the ground. It's generally brighter than the full moon.
These are rather rare. Superbolides don't happen very often, but when they do they get
a lot of attention if it's over land. So a fireball's a meteor brighter than Venus, and
a superbolide is a meteor brighter than the full moon. What happened over Russia was most
definitely a superbolide. So, how does this work? In space, you've got
a hunk of rock, a meteoroid. It hits the atmosphere, it burns up, or if it's bigger it breaks apart
into little pieces which burn up, and when it gets down to about 10 to 30 miles above
the surface of the Earth, the atmosphere slows those things down so low they're no longer
burning up and they stop emitting light. So you've got something blazing through the atmosphere
and if it gets deep enough down the atmospheric drag slows it down to the point where they
get below 3 miles a second and stop emitting light. At that point they no longer are ablating
and we call from that on dark flight because we don't see them anymore. They're just dark
chunks of rock and they fall, and boom if anything makes it to the ground you have a
meteorite.