Re: Reflections from a smooth vertical cylinder (tether) Further reflection (pun intended) indicated I gave only the optimal circumstance. Reflections at all angles can be possible, but the geometry is less simple to describe. In all of these, the angle of the Sun above the tether "equator" is equal to the reflected angle below it. I believe the cirmumstances for a reflection at a specific moment is defined by the intersection of a cone with the Earth's surface. The tether is at the cone's tip and has its axis along the tether. The angle of the axis to the slope of the cone equals the solar zenith distance (90 - elevation) as seen from the satellite. Points on this intersection would witness a reflection. Hopefully this is correct, but probably pointless! Rob McNaught rmn@aaocbn1.aao.gov.au