[Prev][Next][Index][Thread]
Re: (meteorobs) Nov. 12/13 Summary
In a message dated 96-11-14 10:18:11 EST, you write:
<< >At 10:10 AM 11/13/96 -0500, you wrote:
>>>Judging by the short time of 11 or 12 seconds from meteor sighting to
booming
>>>noise...the meteor had to be very close to you somewhere along it's
>>>trajectory(about 2 miles). Right off hand, if the meteor came that close
to
>>>you, I'd expect a possible louder sonic boom....
>Can a meteor really get this close to you and still be visible? I thought
the general limit would be around 20 miles! The one Povenmire heard in 1972
(I saw it but from further west) he determined it ended at 14 miles true
height which he considered to be unusually low. At 25o elevation I would
expect it to be much further away than 2 miles, even 20 miles. I suspect
some coincidental ground sound here. Sounds from meteors ought not be less
than about 2 full minutes.<
I think you are right Norman. Using rough estimates here, I believe a
meteor would have to be on the order of 10 tons in mass to still have cosmic
velocities intact by the time it reaches about 2 miles above the earth.
Anything less massive would have varying percentages of the cosmic velocity
intact by the time it reaches the ground. But sonic sounds from the
literature that I have read indicates sonic booms can occur if the meteor
reaches a point that is about 30 miles above the earths surface. Assuming
that the fireball was directly overhead ...the closest point at this time, it
would take about 2.5 minutes for the sound to reach you. Surely a near 10
ton meteor would make one heck of a sonic boom...probably a series of them
with a long rumbleling noise reported from many places. The approx -15
Fireball that Lunsford and I witnessed in Dec 1992 made a single very loud
sonic boom that sounded as loud as the thunder a lightening strike would make
within a block away from you. The sonic boom took about 2 min. and 43 seconds
to reach us after it's appearance. I was able to get these times because I
had my chart recorder going at the time monitoring fm radio forward scatter
signals. As soon as the sonic boom occurred, I think both of us instinctively
knew what it was and we instantly looked at our watches. It was very exciting
for both of us.
Mark, you seem to have a paradox here...an apparently small meteor going fast
enough to make a small sonic boom in such a short period of time to you.
I have been long overdue...10+ years and only a -6.0 to show for it before
>>this one. But didn't you and Bob catch a -12.0 last year I think? Still
have
>>to catch up to that one....
I didn't see that -12 that Bob saw last year or actually more recently I
think? He was observing without me that nite.
>I have only two -12's in 36 years of observing. First was a blue -12
Leonid
1979 Nov 22 with a ten-minute train. Second was a blue -12 Taurid in 1994 (
I forget which branch) with a brief train. Since Povenmire sees almost
every meteor 2 magnitudes brighter than mere mortals, he has a whole bunch
of -12's (several in 1974 alone). And I'm still waiting to hear one. Seems
like it would have to be very high in the sky to be close enough for you to
hear. Povenmire was right under the one in 1972, and again in 1973 Aug for
a repeat performance! I saw the latter one as well, again from much further
west thus putting it only 15o up from my site.<
Norman
>>
The one that bob and I heard appeared right in front of my eyes ...center of
view...at about a 70 degree angle I guess. Then came down and over to an area
about 45 degrees above the horizon.
George Z.