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Re: Satellite re-entry?



Mike73@aol.com wrote:

>>Last evening, at approximately 0225Z, I saw what appeared to be a satellite
>> re-entering the atmosphere.  It was bluish-white in color and tracked from
>> NW to SE, the starting azimuth from my location (EM28) was about 30 
> 
> degrees.
> 
>> Anyone know what bird this may have been?
> 
> 
> James,
> 
> I think you may have seen a meteor. The Perseids is happening now.

A good way to distinguish a meteor from a re-entering satellite is by 
its speed. Earth-orbiting satellites usually re-enter from a low, 
circular orbit, so they have a characteristic velocity of about 7 km/sec.

Meteors move much faster. They come from well beyond the earth, so they 
always hit us with at least the earth's escape velocity, about 11 
km/sec, and usually much faster still as they're accelerated by the sun 
before being captured by the earth. The earth's orbital velocity around 
the sun is about 30 km/sec, and depending on the meteor's orbit around 
the sun its relative velocity to the earth can be quite a bit higher.

Since the Perseids come from a cloud of particles in a fairly fixed 
orbit (debris from the comet Swift-Tuttle), they hit the earth with a 
characteristic velocity of 59 km/sec. This is *much* faster than a 
satellite re-entering from low earth orbit!

Phil

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