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Re: (meteorobs) New Member Peter Stinson & Request fo
In a message dated 99-06-18 16:39:00 EDT, you write:
<< lew Gramer wrote:
>BTW, Mr. Zay's exceptions to the criteria I mentioned all have validity.
Except
however, that I have not heard of bright fireballs near the horizon
appearing
foreshortened or seeming to "hang in the sky" the way a flare might. What
is
supposed to produce this effect, anyone?<<
George K>> Lew: I believe the effect George Zay referred to results thusly:
given two
objects having the same true velocity, one nearby, the other quite distant,
the apparent angular velocity of the more distant object will be
considerable less than the nearby object.<<
George, This is exactly what I'm alluding to. what you said above is correct.
George K>>For example, if a meteor at a distance of 200 km were to appear to
travel
10 degrees in one second, and you were to remove this meteor to a distance
of 2000 km, its apparent angular velocity would be reduced by a factor of
200/2000, or to 1/10th of its observed angular velocity ( to 1 degree per
second) when it was nearby. By the same token, if the meteor had a visual
track of 30 degrees when it was seen from a distance of 200 km, it would be
reduced in apparent length by the same factor of 1/10th, or to 3 degrees
when seen from a distance of 2000 km, thus the "foreshortening" alluded to
by George. It is all a matter of perspective.
George Kelley<<
This is also part of the cause for some distant aircraft lights or contrails
(particularly those heading towards or away from an observer.) to be
responsible for some UFO sightings. The lights or reflected sunlight off a
contrail after sunset appears quite stationary or nearly so for a seemingly
long time.
GeoZay
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