Been an interesting week, skywise. We had that asteroid, 2012DA14, approach earth on Friday. I was sitting in a conference session Friday afternoon and at 2:25 I strained to hear or feel something for about 10 minutes, but, of course, I didn’t. An asteroid is pretty much anything orbiting the sun that’s smaller than a planet. This is a large range. Friday’s asteroid was a teensy fraction of the size of the earth, even though that’s still pretty huge. Little wonder I didn’t feel anything.
When something enters our atmosphere and glows in the sky, we call it a meteor. An asteroid can be a meteor. Most meteors are smaller than 2012DA14. A meteor that actually strikes the earth is a meteorite.
The meteorite that landed in Siberia Friday had a radius of about one meter, according to the estimates I’ve seen, though nobody’s sure, exactly. That works out to a weight of about 10 tons, which amounts more or less to 3.5 rhinos or 2 Hummers. It’s iron, and you certainly wouldn’t want to be hit by it, coming down as it did, with a velocity of about 16,000 m/s.
The asteroid, 2012 DA14 has a radius of about 25 m, and while neither the asteroid nor the meteorite is all that spherical, using an estimated radius helps compare their sizes. The volume of a sphere is proportional to r^3, so the asteroid had a volume (and weight) that was about 15,600 times bigger than that of the meteorite. Little wonder that nobody saw the meteorite coming.