sun + spot

Chinese astronomers recorded dark spots on the sun as early as 364 BCE, visible to the naked eye through atmospheric haze at sunrise and sunset. Theophrastus, Aristotle's student, mentioned them around the same period. But European science largely ignored sunspots until 1610, when Galileo, Thomas Harriot, Christoph Scheiner, and Johannes Fabricius independently observed them through telescopes. Scheiner initially claimed they were small planets orbiting close to the sun. Galileo argued they were features on the sun's surface. Galileo was right.

Sunspots are regions where intense magnetic fields — thousands of times stronger than Earth's — inhibit convection, preventing hot plasma from reaching the surface. The result is a patch roughly 1,500 degrees cooler than the surrounding photosphere. They appear dark only by contrast; a sunspot isolated in space would outshine the full moon.

In 1843, Samuel Heinrich Schwabe, a German pharmacist and amateur astronomer, announced that sunspots follow an eleven-year cycle. He had been watching the sun daily for seventeen years to prove his point. The Schwabe cycle, as it is now called, drives space weather: solar flares, coronal mass ejections, and geomagnetic storms all peak with sunspot activity. The 1859 Carrington Event, the most powerful geomagnetic storm on record, occurred during a sunspot maximum.

The Maunder Minimum — a period from roughly 1645 to 1715 when sunspots nearly vanished — coincided with the coldest part of the Little Ice Age in Europe. The connection between solar activity and terrestrial climate remains debated, but the correlation is striking. The dark spots on the sun may have frozen the Thames.