Solar coordinate systems

In solar observation and imaging, coordinate systems are used to identify and communicate locations on and around the Sun.

It lacks a solid or liquid surface, so the interface separating its interior and its exterior is usually defined as the boundary where plasma becomes opaque to visible light, the photosphere.

Since plasma is gaseous in nature, this surface has no permanent demarcated points that can be used for reference.

[1][2] In observations of the solar disk, cardinal directions are typically defined so that the Sun's northern and southern hemispheres point toward Earth's northern and southern celestial poles, respectively, and the Sun's eastern and western hemispheres point toward Earth's eastern and western horizons, respectively.

[10][11][12][7]: 278 Heliocentric coordinate systems measure spatial positions relative to an origin at the Sun's center.