Solar Disk Imaged by Eric Grieve

A sunspot is an area on the Sun’s surface (its photosphere) that appears dark because they are cooler than the surrounding area  – approximately 4,000–4,500 K compared with the 5,800 K of the surrounding material at about 5,800 K .  They are visible as a dark spot because the intensity is a function of temperature to the 4th power (Stefan–Boltzmann law).  Sunspots are caused by intense magnetic activity which inhibits convection, forming areas of reduced surface temperature.

Image taken on 01 July 2005