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Re: (meteorobs) P/2000 G1 & Vgeo
At 03:40 PM 6/1/00 -0400, Lew wrote:
> >From the observer's perspective on the ground, what you call Va is
> important:
>and as conventional wisdom states, this has a hard minimum at around 11 km/s.
Remember that this "hard minimum" does not include atmospheric drag, which
will affect the observed/photographed speed of the meteor to some
degree. Another very tiny effect on the observed speed is the that due to
the rotation of the Earth, called diurnal aberration (but no more than
about 0.46 km/sec maximum for an observer at the equator and a meteor
heading directly east or west). These other minor effects help to explain
the answer to the next question:
>One mystery still remains, though: I would assume that the Velocities stated
>in the IMO Radiant database are actually what Jim calls Va. So how is it that
>two of the showers in that database (Corvids and Camelopardalids) have values
>for 'Vel' that are below 11 km/s?? Is it simply error, or is the IMO database
>actually quoting Vg rather than Va - or is something else going on?
I do not have the lists handy here at the office to verify this, but I
think that the IMO list of meteor streams (and Cook's list before it) list
the ACTUAL average photographic or radar meteor speed for each
shower. Cook's paper also gives the sample size used for the speed
calculation in some instances. These speeds are the true observed speeds,
which would include all factors, major and minor. The scientist must then
work backwards to solve for Vg and thence Vh.
A final nomenclature note:
The atmospheric entry speed, what I called Va, often has another symbol: V
subscript (the infinity symbol), or Vinf [V_\inf in LaTeX]. This seems
even more confusing to me, so I simply used Va in the last post. Also, in
both conversation and in writing, the term "geocentric speed" is *still*
sometimes used for Va, although not properly so. The terms "atmospheric
speeds," or more commonly "photographic speed" convey the meaning better.
Best regards,
Jim
------------------------------------------------------------------------
James Richardson (graduate student)
Department of Planetary Sciences
Lunar and Planetary Laboratory
University of Arizona
Tucson, AZ 85721
school email: richardson@lpl.arizonadot edu
school webpage: http://www.lpl.arizonadot edu
Operations Manager
American Meteor Society (AMS)
AMS email: richardson@amsmetoers.org
AMS webpage: http://www.amsmeteors.org
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