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RE: (meteorobs) New Member Peter Stinson & Request for Info...



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?<

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.

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


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