Calculation of Iridium Flares

From: Johannes Bauer via Seesat-l <seesat-l_at_satobs.org>
Date: Fri, 05 Jun 2015 20:42:09 +0200
Hi list,

I really hope this is the correct place to ask my question, if not, I'd
appreciate a hint where it'd be more appropriate.

I'd like to write a program that calculates Iridium Flares (or similar
artificial sattelites). My knowledge about astronomy is intermediate,
I've written a program that calculates planets rise and set times given
a location on earth from the orbital elements data.

My guess is that calculation of Iridium Flares is more complicated since
not only the sky position is relevant (as it is for planets), but also
the angle in which the sunlight is reflected to give a "flare".

Now for starters I've compared data of "Heavens Above" with the output
of http://iridiumflares.sourceforge.net/ (by Emmanuel Zurmely). The
latter has the advantage that the source code is open and available and
I'd intend to borrow from it (my tool would also be open source of course).

To get a bit of a impression of how precise predictions are, I've
checked plausibility of data against each other. The results vary quite
a bit, which is a bit odd.

For example, for pos = 49°N 10°E   elev = 400m

"Heavens Above" generates (all times UTC):
Jun 6, 00:23:04	-2.2	51°	159° (SSE)	Iridium 35
Jun 6, 01:59:47	-4.1	38°	110° (ESE)	Iridium 52
Jun 6, 22:40:53	0.0	50°	215° (SW)	Iridium 91

And iridiumflares.sf.net for the same day:
Jun 6, 00:23:05	-1.3	51°	159°	Iridium 35
Jun 6, 01:59:47	-2.7	38°	110°	Iridium 52
Jun 6, 21:14:16	-2.4	29°	266°	Iridium 20


The first two matches are pretty close, the brightness magnitude values
are off quite a bit though. But I'm guessing these are ballpark figures
anyways.

The third flare of HA isn't counted by the Java program. Probably
because it's too dark. But the third flare predicion of the Java program
is missing entirely on HA. What could be reasons for this?

Is there a good introduction that I could follow to get the calculations
done? I'd like to calculate some of this stuff with a pen & paper method
so I understand what I'm doing and can replicate the results.

Any help/hints greatly appreciated!
Best regards,
Johannes

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Received on Fri Jun 05 2015 - 13:42:56 UTC

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