What Causes a Sunspot and When Were Sunspots First Discovered?

Sunspots seem to be visual evidence of magnetic disturbances in the Sun’s convective or radiative layers.

In other words, sunspots are areas of highly intense magnetic energy, which are dark because they are much cooler than their surrounding areas.

They usually occur in pairs, and sometimes in groups.

The center of a sunspot, known as the umbra, is very dark; the edges, or penumbra, are lighter.

The umbra is the center, or darker area, of a sunspot. The brighter penumbra forms a “shadow” around the umbra.

The first historical evidence of a sunspot sighting comes from the fourth century B.C.

At first, people believed that sunspots were planets orbiting the Sun, until Galileo declared that the spots were actually on the Sun’s surface.