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Re: (meteorobs) observed magnitude



At 09:45 PM 12/9/99 -0600, you wrote: 
>>>>
A hypothetical example: Two people see the same meteor from different
locations. The first observer sees the meteor near the radiant. Its burn
path covers a mere 7 or 8 degrees. The second sees it cover 45 degrees
during the same time span.
Will both observers perceive the same magnitude or will the first observer
consider it to be brighter?
-------------

Hello Tom,

A lot will depend upon the initial conditions given for the problem, such
as shower radiant altitude and position angle of the meteor with respect to
the radiant.  As an example, however, I have used a visual meteor model
that I have recently been developing to generate a hypothetical Geminid of
magnitude 2, radiant altitude of 45 deg, and meteor-radiant  position angle
of 45 degrees from the zenith direction.
  
This gives the following numerical results, for a meteor beginning at 5 deg
from the radiant, and a meteor beginning at 45 deg from the radiant:


1. Geminid, 2nd mag, radiant alt = 45 deg, meteor p.a. = 45 deg, beginning
distance from radiant = 5 deg:

height 1 = 104.0  km
height 2 = 85.3  km
path length = 26.1  km

duration  = .76 sec
length = 1.16 deg 
angular speed 1 = 1.24 deg/sec
angular speed 2 = 1.89 deg/sec 

average distance = 125.2 km
altitude = 48.7 deg
mag extinction = +.49  mag


2. Geminid, 2nd mag, radiant alt = 45 deg, meteor p.a. = 45 deg, beginning
distance from radiant = 45 deg:

height 1 = 104.0  km 
height 2 = 85.3 km 
path length = 26.2 km 

duration = .76 sec
length = 10.2 deg 
angular speed 1 = 11.5  deg/sec 
angular speed 2 = 15.5 deg/sec 

distance  := 113.0 km 
altitude = 56.6  deg
mag extinction = +.27 


Note that the difference in the magnitude extinction between these two is
quite small, only about 1/4 magnitude.  The real observed differences lie
in the angular length of the meteor, and in the angular speed of the
meteor.  The 2nd mag Geminid appearing near the radiant moves much, much
slower, and covers only a bit over a degree in length, while the meteor
that is farther from the radiant will have a significantly greater path
length and apparent motion.

Best regards,

     Jim


James Richardson
Department of Physics
Florida State University (FSU)

Operations Manager 
American Meteor Society (AMS)
http://www.amsmeteors.org
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