Hi Tom, Have been following your updates on the ISS/Venus transit for next week, and thought I'd point out one factor that should simplify your analysis. In one of your recent posts, you wrote: "Atmospheric ray-bending would have the effect of moving the shadow in the direction of the ISS; effectively equivalent to increasing the observer's elevation above sea-level by 75 meters, in this case (which, given a range of 839 miles, would not be very significant)." There is no need to complicate your analysis by computing refraction. For a ground-based observer, refraction will bend the light rays from the Sun, Venus and ISS by equal amounts. Thus, the apparent position of ISS relative to the Sun/Venus would be identical, even if the earth had no atmosphere. By far the greatest source of uncertainty in the ISS transit calculation is the accuracy of the TLE itself. For example, one big solar outburst in the next day or two would change all your predictions. Cheers, Rob ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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