Re: Satellites in Eclipse
Bjoern Gimle (b_gimle@algonet.se)
Sun, 15 Feb 1998 09:40:37 +0100
Russell Eberst wrote:
>
>On February 26, 1998 there is a total eclipse of the Sun. Some of you will be
>travelling to Central America or the Caribbean to experience this wondrous
>spectacle of nature. Satellites too can experience eclipse, cutting down the
>light that they reflect for us to be able to observe them. An inspection of
..
>would be interesting to investigate if any of these is likely to disappear, not
>in the Earth's shadow but into the Lunar shadow.
>
>06153 OAO 3 06207 Cos521R 12457 Meteor2-7R 12465 Cos1271R
>12443 Cos1269R 10856 OTS 2R 04391/2 Mao 1 & R 19195 Cos1950
>15595 Geosat 25039 Iridium43 25040 Iridium41 25043 Iridium38
>23793 Cos2328R 24285 Fast
>-----------------------------------------------------------------------------
I have used SkyMap to predict some possible satellite eclipses during
the Feb.26 solar eclipse.
The F9 Sun and Moon positions define the central line of totality at
any given time; the angular size defines how far the totality cone extends
beyond the cone. If you set the latitude, longitude and height (and time)
of this point in SkyMap, and a small field pointed at the Sun, you will
see the Sun occulted by the moon (same size), and all satellites that
are eclipsed will pass over the Moon's disk.
Unfortunately, since the cone tip moves about 80 km per minute, and the width
at LEO heights is only about 100 km, you should probably make one prediction
per minute for reasonable accuracy. You can set an interval to 0:04, and
a field width of 4 degrees or so, to see possible candidates, and estimate
the track displacement until the actual pass time. Remember to set the
max.range high to compensate for the position of the tip, min.elev. and
culmination to -89, and no constraints at Lighting / ground site.
A sample plot showing #22285 92-93B eclipsed at 19:18:28 UT is available at
http://www.algonet.se/~b_gimle/gif/solare11.gif
, and another showing #12457 81-43B at 19:19:54 UTC as ./gif/solare12.jpg
Time Lon Lat H
Tip 14:09 -157.909 -1.801 9314k
Tip 15:09 -182.150 2.273 6627k
Tip 19:09 43.233 23.038 5414k
Tip 19:19 40.620 23.222 5771k
Tip 19:29 35.613 23.365 6132k
Tip 19:39 30.803 23.448 6527k
Tip 20:09 17.139 23.51 7797k
The positions for 19:18 and 19:20 plots have been interpolated from the
table above.
My Excel computations are available in the ./solarecl.xls file -
please recheck them, or use another method ! A sample SkyMap for plots
is ../solare12.cfg.
Before the eclipse, some objects may be seen eclipsed over the central
Pacific, maybe even some high-altitude ones from New Caledonia.
The width of penumbra at LEO heights is about 7000 km. If you want a
reasonable brightness change, try to predict objects less than 1000 km
from the center line. This area is approximately a 0.7 degree cone
viewed from about 150000 km behind the Earth (where the Moon covers half
the area of the Sun!)
Penumbra 19:29 68.530 9.832 151996k
Penumbra 20:09 57.665 10.06 152265k
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