Science & history · An active star
Sunspots are cooler, magnetic regions
Sunspots look black only by contrast. On their own they would shine brightly.
What they are
Sunspots are cooler regions caused by concentrated magnetic field lines, the visible part of active regions where the magnetic field is intense and tangled, and where eruptions start. NASA gives their size as about 1,600 to 160,900 kilometres across.
Watched for centuries
Chinese official histories describe one in 28 BC as a black gas like a coin at the centre of the Sun, and record more than a hundred notable spots by 1638, all without telescopes. Looking at the Sun directly is how people damage their eyes; project it instead.
Sources
- NASA and NOAA Sun Reaches Maximum Phase in 11-Year Solar Cycle (15 October 2024) (opens in a new tab) for solar maximum announced; the peak month is identified only in hindsight; May 2024 storm · checked 2 October 2026
- NASA Sun: Facts (opens in a new tab) for age, size, distance, temperatures, layers, rotation, cycle, type, future · checked 2 October 2026
- NASA Yohkoh archive (A. Davey, 2002) A Little Bit of (Naked Eye) Sun Spot History (opens in a new tab) for the 28 BC record ('a black gas … like a coin'); 112 notable sunspots in Chinese histories to 1638 · checked 2 October 2026