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(meteorobs) Zenethal Attraction
About zenithal attraction:
Meteoroids in a stream suffer from the gravitiy of the Earth. Their
trajectories are bended in a way towards the center of the Earth. When a
meteoroid enters the atmosphere after attracted by the gravity it appears
to cause a meteor from a radiant which is higher in the sky than the actual
radiant calculated from the orbit would be. Slow meteoroids are more
strongly affected. The formula to calculate the zenithal attraction is:
delta z = 2 tan^-1 ( (v_g-v_inf)/(v_g+v_inf) tan (z/2) )
where delta z is the desired shift in zenithal distance of the radiant. v_g
is the geocentric velocity (that is, without Earth's gravity), v_inf is the
velocity after gravity has acted and is calculated approximately by
v_inf= sqrt( v_g^2 + 125 )
z is the original zenith distance of the radiant according to the
equatorial coordinates and time. Zenithal attraction is usually small,
smaller than the radiant diameter of a meteor shower. Just for very slow
streams like the pi-Puppids, this shift may be of interest to the visual
observer.
Rainer Arlt
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Visual Commission
International Meteor Organization
email: visual@imodot net
Homepage: http://www.imodot net
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