The image from the Solar and Heliospheric Observatory spacecraft assigns false colours to reveal details on the Sun's surface.
The light receptor cells-known as cones-in the human eye, are considerably less sensitive than the cells responsible for distinguishing light and darkness-known as rods. As a result, in dim light we are barely able to discern colour-as the saying goes: at night all cats are grey. Therefore, most stars appear to us to be white-only in the very brightest stars can we see traces of colour. For example, the star Antares in the constellation Scorpius appears to be reddish. The colour of a star enables astronomers to gauge its temperature. Red stars are cooler than the Sun, while blue stars are very hot.