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Re: meteorite-impact physics item


>>Of course, from this one question flows many other questions: 

1)  Have there been falls in which there were sonic boom(s) but no
apparent explosion was witnessed?<<

I have personally witnessed such an event in  December of 1992 while recording
data on the Geminids with Robert Lunsford. A -15 sporadic fireball that did
not explode , produced a very loud sonic boom just like a jet does when it
breaks the sound barrier. I'm thorougly convinced that it dropped a meteorite
to the ground. Probably the only one out of about 350 fireballs that I have
witnessed and recorded data on. At the end of its visible light phase, it
suddenly turned a dull red ...very much like a lit cigarette thrown in the
dark. It traveled like this for about 2 or 3 degrees and then it suddenly
extinguished. When the red light blinked out, I had the impression that a dark
object continued along the path before I wasn't able to make anything out
anymore. Then 243 seconds later, the sonic boom hit. I was recording meteor
data at the time. I also had my chart recorder hooked up to my radio to record
meteor forward scatter signals on an fm frequency. The meteor's entry time was
very accurately recorded. The signal lasted 18 seconds. It was witnessed by
some locals as well who reported it as a plane crash to the various fire
departments. I personally guestimated from the info I had and the few
witnesses I was able to talk to, that it probably landed in a mountainous area
roughly west of Mt Palomar observatory of all places. I judged the meteor's
entry velocity to have been slightly slower than the Geminids I was watching
at the time. Unfortunately I wasn't running a camera, but made a very good
plot on my meteor charts. I recall wrting David Levy at the time who was at Mt
Palomar in hopes that perhaps someone there either saw it, or might have had a
wide angle camera running that might have photographed it. My letter to levy
was ignored. Due to the mountainous region, I didn't bother making an effort
searching for any meteorite. The whole experience along with my data is
entered in IMO's WGN Journal for February 1993 on page 47. 


>>2)  How does the sound of an exploding fireball compare to the sound of
a sonic boom?<<

My guess it probably sounds the same with no distinction.

>>3)  At what size/shape will a falling object be small enough not to
generate a sonic boom?<<

This is a question I've been asking for several years within the International
Meteor Organization. I have never got an answer.  I think there must be a
minimum size? I have not heard any fireball reports that reported sounds that
resembled that of a high powered rifle bullet being heard. But then perhaps a
meteoroid that is small, may not be traveling fast enough to create a sonic
boom that doesn't get absorbed in the air by the time it reaches the ground to
be heard? The velocity of the bigger objects that are heard is maintained a
little further and perhaps the sonic sounds are able to bully it's way thru
the air before getting dissipated? From what I've learned, a meteoroid needs
to reach an area at least 30 miles above the earth in order for a sonic boom
to be heard on the ground. The air is thinner there and the transmission of a
sonic from a very small object may not be very efficient. By the time this
small object reaches a low enough altitude where air can effectively carry
sonic sound waves, it will be traveling too slow to create one. At least this
is how I picture it?

George Zay