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(meteorobs) Tom's Hypothetical Geminid
At 01:22 AM 12/10/99 -0500, some nerd (me) wrote:
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1. Geminid meteor, 2nd magnitude (absolute), radiant altitude = 45 deg,
meteor-radiant position angle = 45 deg from zenith direction, initial
meteor distance from radiant = 5 deg:
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>duration = .76 sec
>length = 1.16 deg
>angular speed 1 = 1.24 deg/sec
>angular speed 2 = 1.89 deg/sec
>height 1 = 104.0 km
>height 2 = 85.3 km
>path length = 26.1 km
>average distance = 125.2 km
>average altitude = 48.7 deg
>mag extinction = +.49 mag
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2. Geminid meteor, 2nd magnitude (absolute), radiant altitude = 45 deg,
meteor-radiant position angle = 45 deg from zenith direction, initial
meteor distance from radiant = 45 deg:
>duration = .76 sec
>length = 10.2 deg
>angular speed 1 = 11.5 deg/sec
>angular speed 2 = 15.5 deg/sec
>height 1 = 104.0 km
>height 2 = 85.3 km
>path length = 26.2 km
>average distance := 113.0 km
>average altitude = 56.6 deg
>mag extinction = +.27
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I have been busy for a couple of days, but here is the additional numbers
you asked for:
3. Geminid meteor, 2nd magnitude (absolute), radiant altitude = 45 deg,
meteor-radiant position angle = 0 deg from zenith direction, initial meteor
distance from radiant = 40 deg:
duration = .76 sec
length = 11.4 deg
angular speed 1 = 12.1 deg/sec
angular speed 2 = 17.9 deg/sec
path length = 26.4 km
height 1 = 104.0 km
height 2 = 85.3 km
average distance = 95.1 km
average altitude = 84.2 deg
magnitude extinction = -.11 mag
This gives the following magnitudes for the meteor when comparing to nearby
stars:
met 1 = 2.49 mag
met 2 = 2.27 mag
met 3 = 1.89 mag
In this example, since all of the meteors are above 45 deg of altitude,
their magnitude extinction values (due to the inverse square law only) are
rather low. This effect is much more drastic when lower meteor altitudes
are considered.
if the complete magnitude extinction effect is taken into account, for both
the inverse square law and atmospheric absorption, The effect on this
example is a bit larger:
met 1 = 2.74 mag
met 2 = 2.41 mag
met 3 = 1.84 mag
these are the magnitudes that would be obtained if the observer called off
the magnitude based upon perceived brightness alone (without comparison to
nearby stars), or if the meteor was compared to stars in the vicinity of
the zenith. The method outlined in the first example is the recommended
one to use today because atmospheric absorption is somewhat variable and it
can be corrected for in the field by comparison to nearby stars (which
undergo this same extinction).
With regard to how the eye will perceive this meteor, this is not my area
of expertise, so I won't comment except to say that the human eye's
integration time is rather short from what I know -- something on the order
of 1/25 - 1/100 seconds. (CRT frame rates are designed around this).
Regards,
Jim
BTW; please also keep in mind that my mathematical model is just that -- a
model, which has yet to be validated. The most difficult part is the
beginning and terminal meteor heights, and for now these are empirically
derived from photographic data given in McKinley (1961).
James Richardson
Department of Physics
Florida State University (FSU)
Operations Manager
American Meteor Society (AMS)
http://www.amsmeteors.org
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