I'm trying to figure something out that I thought was going to simple but after mediating on it I realized that it's not simple at all. It seems to have implications about the relative motion of a satellite though one's sky, but I'm not sure. This is my line of thought. I wanted to know the km per second ground speed of the ISS over my town at 42.5 degrees latitude. I first had the mistaken idea that its listed orbital speed in km/s was its ground speed. Duh, I thought as I began to reason what that meant. I thought, it's above the globe thus it covers more distance in one revolution than the earth is in circumference. I then thought, I will just consider the satellite's period and the circumference of the earth. Wait, that won't work! Alas, the earth's rotational ground speed itself contributes to the net ground speed of the satellite passing overhead. After that came the remembrance that the ISS orbit has an inclination that is much greater than 0 came to mind. Oh no, that means that the earth's ground speed varies with the latitude under the ISS, and really messes things up! Well I have given up trying to figure out how fast the ground speed of the ISS is over my town or anywhere else for that matter. I'm now sure it's latitude dependent. Can someone verify that the "ground speed" of the ISS is latitude dependent? Does that make a difference how fast it moves across one's local sky? Finally, how much does the ground speed vary with the ISS? Thanks, Tom Iowa USA ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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