Don McCarthy's Questions of the Week

How far away is the horizon? If a tall adult (h = 6 feet) looks out to sea, how far away can she see? Use geometry to develop a simple formula for the distance to the horizon from any height. You may neglect effects of the Earth's atmosphere. Assume Earth is a sphere of radius "R = 3960 miles." How far away could you see from an airplane at altitude 30,000 feet?

If we choose to include atmospheric effects, how do you imagine these results would change? What might be special about your horizon on worlds like Venus and a neutron star?