ABSTRACTHigh latitude flying in modern high‐speed aircraft is hampered by lack of navigation facilities, and also by long periods of twilight during which no astro navigation is possible. Standard methods of twilight computation are applicable, but in practice have been cumbersome for the special purpose required. A simple computer is described, by means of which twilight conditions on any proposed flight can be found. Its further application to other problems is described as well. In addition a simple and improved planisphere for high latitudes is include