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(meteorobs) Distance for simultaneous meteor observation, further examples.
Hello folks,
My prior message on this subject, was based on one representative meteor
height, 50km only. Since this is highly variable, with meteors being
visible from heights below 20km to over 100km, I would like to
illustrate the different distances of visibility as a function of meteor
height.
Reviewing the formula:
d = distance from observer to meteor sub-earth point (which is the point
on the earth directly below the meteor). (d is measured along the earth
surface in km)
A = altitude of meteor as seen by observer (degrees).
h = height of meteor above the earth surface (km).
R = radius of the earth (km).
we get:
d = (pi/180) * R * [ARCCOS(COS(A)/(1+h/R)) - A]
Now, lets calculate "d", the distance of the meteor from the observer,
for heights of 20, 50, 80 and 120 km, at various observed altitudes:
............ Meteor height .........
............ 20km 50km 80km 120km
Observed Alt
............
0 deg 503km 795km 1003km 1225km
3 deg 270km 528km 723km 936km
5 deg 194km 414km 590km 789km
10 deg 108km 253km 383km 539km
20 deg 54km 132km 208km 303km
30 deg 34km 85km 134km 198km
45 deg 20km 49km 78km 117km
The maximum distance 2 simultaneous observers could be apart to still
observe the same meteor, at each of these conditions, would be twice the
value of "d" given above.
It is obvious that there is a wide range of maximum inter-observer
distance, and depending on the characteristic of the meteor and at what
height it burns up, it will be between ~400km for very low meteors, and
~2000km for the highest ones.
However, if you are considering a simultaneous observing session, you
want both observers to see most of each others meteors, not just the
ones at the extreme limits. Therefore, the optimum inter-observer
distance will be much less than these maximum values!
For example, assuming the 2 observers each have a 100deg FOV, and are
looking directly towards each other at an altitude of 50deg, and
considering normal atmospheric clarity and average meteor magnitude, we
should limit the meteors to above 20deg altitude. The meteor heights are
highly variable, but, lets use 50km as a conservative value, for the
brightest or terminal burst phase. Then, from the table above, such a
meteor would be 132km from the observer. To ensure observer #2 can see
every such meteor above 20deg for #2, as seen by observer #1 at the
extreme top edge of FOV of #1, the interobserver distance should be
132km- 50*cos(80) = 123 km.
Good observing for the QUA! Here in central California, the forecast is
calling for increasing clouds and rain by Tuesday afternoon, so it could
be a close call late Monday night.
Mike
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