Written by Kelly Herbst, Astronomy Curator for the Virginia Living Museum. Updated every two weeks, more or less.

Wednesday, April 25, 2012

Smoke on the Water and Fire in the Sky

Well, I don't know about the smoke on the water part, but last Sunday in Nevada and California there was definitely some fire in the sky.

It's now fairly certain that the explosion reported by so many folks in those two states was a bolide, or a fireball.  Fireballs are large meteors that are generally very bright, and are usually accompanied by a good deal of noise.  Most often they explode in the air - a result of the stress of passing through the Earth's atmosphere.  But what is a bolide, really?

Simply put, it's a shooting star.  A very impressive one.

Shooting stars are not actually stars.  They are meteors - rocks from space which enter the Earth's atmosphere.  Most are extremely tiny - like grains of sand or dust.  The friction caused by all that air rubbing against the rock actually makes the air glow - that's the streak of light we see and call a shooting star.  Tiny dust-fragments never get that far - they disintegrate and are gone before they can heat up enough air for us to see.  Larger chunks make a distinct streak of light, but they actually don't make it very far into our atmosphere either before they too are destroyed.  Big chunks, though, can do some amazing things.

A map showing the location of the April 22nd fireball.  Courtesy

The fireball this weekend was clearly seen in daylight.  When the meteor finally burst apart from the stress, it was pretty close to the ground - maybe about 5 miles up.  If it had been higher up, there would not have been so many reports of loud booms.  Based on information gathered from eye witnesses, it's likely that the meteor which caused all the excitement was about the size of a minivan when it entered the atmosphere.  The energy of the explosion has been estimated at about 3.8 kilotons of TNT, so this was a pretty big deal.  Since it exploded above the ground, there was little actual damage, but it's possible some pieces of the meteor may now rest on the ground.  If these meteorites can be found, they would be quite special, as it is rare to be able to so accurately pinpoint the event that a meteorite came from.

A picture of the Nevada/California fireball of April 22.  Credit: Lisa Warren

So don't forget to keep looking up, even in daylight.  You never know just what you might see!
Carpe noctem et diem!

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