Hello, as you all know a satellite orbiting the earth in regularly obscured from the sun when it is in the shadow of the earth. Now, I would like to see the variations of the mean shadowing as a function of time. This mean time in the shadow of the earth will probably be a function of time of the year (indicating the angle between orbital plane of the sat and the plane of the sun), inclination, mean height and maybe some other elements. Is there somebody who knows a *simplified* formula to calculate the mean time in shadow given the date and the orbital elements for that epoch? The output of the formula only has be correct within a percent or so. Greetings, Kurt Jonckheere (kjonckheere@unicall.be)