During the time I was interested in taking pictures of artificial satellites - in particular, the passes of the ISS across the sky and the flares produced by the Iridium constellation - I became aware of multiple different instances where successive events had a definite time relation which was difficult to explain. I thus felt it was time to do some geometry and get my calculator out in an attempt to understand what was going on. This article contains the results of my investigations
The situation with the ISS is fairly straightforward as of course it orbits alone, so cannot have a timed relationship with another Station, and it remains in basically the same orbit all the time. The only thing needing calculation is thus its periods of visibility. To learn more about this, click here.
Photographically, Iridium flares looked the most intriguing as they were bright (sometimes extremely so!) and short-lived thus providing images that could be more than just a uniform faint streak. But what, I hear you say, is an Iridium flare? It was a reflection of sunlight from one of the many first generation satellites providing communications services for the Iridium Corporation. I say "first generation" because they were eventually replaced by newer versions, which (unfortunately for sky watchers) do not flare in such a dramatic way. Any satellite can reflect sunlight of course but Iridium satellites were particularly likely to do so - to find out why, click here.
Information on, and pictures of, both the International Space Station and Iridium flares may be found in the Artificial Satellites chapter of the My Astrophotographs section of the Space Picture Gallery.
