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FW:Re: (meteorobs) METEORS VS FIREBALLS/BOLIDES
From: "E. L. Jones" <jonee@epixdot net>
(I think this bounced due to a funny word, don't worry about it)
Hello,
All bolides are fireballs-- but not all fireballs are bolides.
I have been fortunate enough to have seen two bolides in my life-- up close
and personal. I have seen many fireballs. I can attest that there is a
dynamic and awesome difference in a bolide and a fireball. I believe that
a bolide will always have an aural report (in addition to any sonic
shockwaves i.e sonic "booms"). whether or not the observer is close enough
for it to be heard. I subscribe to the distinction between them is as
follows:
A Bolide ia a body which has a "rapid (explosive) expansion at or near the
end of incandescent flight"
A Fireball is a body which ceases to shine either in burning up or
reaching dark flight (height of retardation) without the explosive
expansion.
The presence and intensity of audible reports, other then sonic boom
generated ones, may have something to do with the altitude and air
density. High altitude explosions are absorbed/depleted faster in the low
gas pressures of the upper atmosphere where much is lost in spanning the
larger gaps in molecule to molecule transmission. The lower altitudes are
much denser and transmit sound energy more effectively. Lower altitudes
and higher densities also act more solidly on the momentum of the
meteoroid. This would create more harsh internal shearing inside the body,
causing it to disintegrate.
All this is to say I believe bolides of stone / iron bodies probably occur
at lower altitudes and are therefore more dynamic than the average
fireball-- if we assume a higher altitude extinction for these. I would
also suggest that a low density , loosely consolidated, comet body will
shear earlier and therefore "explode" higher, but without an audible
report to ground observers.
While the distinction via definition remains subjective, and is
nondescriptive of causes, "bolide" should be reserved for an explosive
variety of fireballs. We frequently make a distinction between fireballs
and run of the mill meteors, do we not? How do we chose to define a
fireball to distinguish it amongst other meteor related phenomena?
Regards,
Elton
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