[meteorite-list] Sonic Boom in Virginia?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 26 Jan 2007 08:45:36 -0800 (PST)
Message-ID: <200701261645.IAA18292_at_zagami.jpl.nasa.gov>

http://www.wdbj7.com/Global/story.asp?S=5991049&nav=menu368_3_6_4

Sonic Boom In The New River Valley?
WDBJ7 (Virginia)
January 25, 2007

Numerous reports have come in to Skytracker7 Forecast Center over the
past 24 hours. Some with meteorite sightings, some with minor shaking in
the New River Valley, and others with a sound of a distant explosion.

After sending our viewer reports to the Virginia Tech Seismology
Department, Martin Chapman (Asst. Professor) indicates he did report
some weak seismic activity at a seismograph in Giles County around 7:55
Wednesday night. After examining the reading, he says it does appear to
be similar to that of a sonic boom, perhaps from the same meteorite that
folks saw at that same time.

John Goss, with the Roanoke Valley Astronimical Society says it was
likely a meteorite the size of a grapefruit to cause a sonic boom. The
meteorite was also reportedly coming in at a low angle which may have
lead to many people hearing and seeing it. Sonic booms happen all the
time around the world as objects (planes OR meteorites) break the sound
barrier. Often, the sonic booms take place over the ocean or away from
communities. (Compare it to: If a tree falls in the woods and no one is
there to hear it, does it make a noise?)

Here's some information I've gathered regarding sonic booms.

SONIC BOOM FACTS

-Air reacts like a fluid to supersonic objects. As objects travel
through the air, the air molecules are pushed aside with great force and
this forms a shock wave much like a boat creates a bow wave. The bigger
and heavier the aircraft, the more air it displaces.

-The Cause

The shock wave forms a cone of pressurized air molecules which move
outward and rearward in all directions and extend to the ground. As the
cone spreads across the landscape along the flight path, they create a
continuous sonic boom along the full width of the cone's base. The
release of pressure, after the buildup by the shock wave, is heard as
the sonic boom.

The change in air pressure associated with a sonic boom is only a few
pounds per square foot -- about the same pressure change experienced
riding an elevator down two or three floors. It is the rate of change,
the sudden onset of the pressure change, that makes the sonic boom audible.
Received on Fri 26 Jan 2007 11:45:36 AM PST