Heliographic

Heliographic is an adjective meaning relating to the sun or to heliography, the ancient and early photographic method that used sunlight to produce images. The term derives from Greek helios, sun, and graphia, writing or description. In modern use it is mostly encountered in astronomy and the history of photography.

In astronomy, heliographic coordinates describe positions on the solar surface. They specify heliographic latitude and longitude for features such as sunspots and solar active regions. The coordinate grid is anchored to the Sun’s equator and rotation; longitudes are defined with reference to a central solar meridian that faces Earth. Two common variants are used in solar data: Carrington longitude, tied to the Sun’s mean rotation, and Stonyhurst coordinates, which align with the Earth-facing view at a given moment.

In the history of photography, heliography refers to early processes that recorded images using sunlight, notably Niépce’s experiments in the 1820s. The term is historical and seldom used to describe contemporary photography, but it appears in discussions of the origins of photographic methods.

Today heliographic terminology remains standard in solar physics and solar observation when discussing charts, maps, and data sets that map features on the Sun’s surface in latitude and longitude.