An Etymological Dictionary of Astronomy and Astrophysics

1. An instrument for photographing the Sun, consisting of a camera and a specially adapted telescope.
   

2. A simple device using a mirror to reflect sunlight to a distant observer. By moving the mirror, flashes of light can be used to send coded messages. The heliograph was a highly effective instrument for instantaneous optical communication over 80km or more in the 19th century.
   

3. Meteo.: An instrument which records the duration of sunshine and gives a quantitative measure of the amount of sunshine.

See also: → helio-; + → -graph.