I recently heard a discussion on the about meteor showers on a radio show. The astronomer-guest mentioned that meteors might only be the size of dust or so. Though he was a bit vague on the details; he had to deal with the host’s apparent previous belief that shooting stars are actually dying stars, so he might have been speaking metaphorically. But thinking about it, I realized that an extreme velocity could cause the same bright flash I thought was only created by larger objects.
A web search turned up mostly guesses at the ‘original’ size of meteorites, but I did find a pertinent, if not entirely conclusive, discussion here. This suggests that speed at entry is far more important than mass, and masses on the order of a kernal of corn might be correct to produce flashes as bright as magnitude +2 depending on the shower.
So is this all correct? If anything, it’s yet another moment to mention the Leonids this weekend, which are supposed to be at their peak.
I think the Leonids are the only thing that’s going to make my birthday tomorrow bearable.
Anyway, this doesn’t really answer the question, but here’s an Astronomy Picture of the Day that has an artist’s impression of a “sofa-sized” meteorite he saw, and it has some links.
Let me venture a guess. KSRO in Santa Rosa? 5:00 p.m.?
That astronomer was me. Yes, most meteors you see are no bigger than a grain of sand or so, or perhaps as big as a grape. The really bright fireballs are bigger, grapefruit size or so. The Leonids do generate those too.
The speed is what gives them their energy; you are converting kinetic energy into light via the equation energy = 0.5 * mass * velocity^2. These are particularly fast meteors since we are meeting them head on (they orbit the Sun in roughly the opposite direction that we do), so their energies are very high.
Ah… I have often fantasised about taking a dump-truck load of sand and gravel up into the path of the Earth’s orbit for one of my gala parties. Just let the Earth run it over and watch the fireworks.
The Terrific Astronomer’s right of course about the grain size. I might add, though, that if you’re out somewhere real dark it’s a treat to see faint meteors that correlate to even smaller particles or so. You have to be lucky enough to be looking in the right place to see them since they don’t last long enough, like run-of-the-mill shooting stars, to let your eye be drawn to them. But you are allowed to see the faintest whisper of light and the addition of a few micrograms of mass to our little globe.
Anybody remember a spectacular meteor event in central Pennsylvania last July that was widely reported in the national press? It was seen from several surrounding states, and was seen from further away than I am in northeastern Maryland (damn, I wasn’t looking). A news item in the current Sky and Telescope magazine says the object was probably the size of a dump truck - so we’re talking a very unusually big meteroid.
A dump truck??? Are you sure? That would have been news in a lot more than “the neighboring states”… I don’t think that any meteorite that large has ever been found, and if people saw it fall and it landed in someplace as populated as Pennsylvania, it would have been certain to have been found in, oh, a matter of minutes.
Just for clarification, by the way, it’s a meteoroid while it’s happily floating around in space, a meteor while it’s burning its way through the atmosphere, and should it last so long, a meteorite after it lands.
I didn’t remember it quite right - S&T says “it would have been the size of a small truck”. Perhaps a dump truck is medium sized? They quote Peter Brown of Los Alamos Lab saying the object probably broke up, and they note its remains probably cover up to 30 km of the rugged Sproul State Forest where recovery would be difficult.
Just for even clearer clarification, “…we shall use the terminology recommended by the Internaitonal Astronomical Union in 1961. The particle, when it is in space, is called a meteoroid; the luminous phenomenon caused when the particle vaporizes in the earth’s atmosphere is a meteor; and if it survives and lands on the groundm, the particle is a meteorite” (Exploration of the Universe, George Abell, Holt Rinehart & Winston 1975). It was in this sense that I referred to the big event that was observed as a “meteor event” and the object as a “meteoroid”.
Yeah, I saw it, or at least I saw a spectacular event around that time-frame, and it was big enough to get people’s attention, right enough, so I’ll assume it was the same event.
A brilliant electric-green fireball, with a tail that was about 10 degrees long. The streak crossed perhaps 50 degrees of sky from my position in northern DE. Simply stunning, and I happened to be looking in exactly the right direction when it became visible. I don’t often get that kind of luck, but WOW!
Thanks for the answers … I was actually wondering if it was you, Bad Astronomer (I didn’t catch the name when listening). Though what I heard was at around 9 or 10 a.m on KQED – maybe you as well, or someone you know?
I was lucky enough that it cleared up fairly well to see a good show, even if I wasn’t completely out in a dark area, it was decently dark in front of us. Even the people we saw who just pulled to the side of the road under streetlights were still observing some of the bright ones.
And I saw a very small number of the really brief ones – interesting to think of how something so tiny is still visible.
I remember the national news covering a recent event, maybe it was that one. Hadn’t they narrowed their search to a small area in a corn field? Did they ever find a trace of the object?
Sorry, didn’t mean to sound as though I was correcting you. I just thought some folks might be curious about the distinction.
And maybe the term means something else in the rest of the world, but where I’m from, a dump truck is a huge earth-moving construction type machine. If one of them doesn’t qualify as a larger than “medium sized” truck, then nothing does.
What distinguishes a meteoroid from an asteroid? Size? If so where’s the dividing line? If not why can’t meteoroids be very large (given that Chronos suggests a dump truck sized one would be nigh ridiculous)
(My other guess is asteroids come from the asteroid belt and meteoroids come from other stuff…ala comets.)
So it wasn’t me, but you actually did hear it in San Francisco? That’s a weird coincidence!
There are lots of astronomers in the area, though the stuff you mentioned did sound a lot like what happened when I was interviewed. I was wondering if she really thought meteors were stars for a moment…
Yes, most meteors you see are no bigger than a grain of sand or so, or perhaps as big as a grape. The really bright fireballs are bigger, grapefruit size or so. The Leonids do generate those too.