Who observed sunspots at the same time as Galileo, leading to dispute?

Christoph Scheiner observed sunspots at the same time as Galileo, leading to a bitter dispute over observation and priority. Scheiner, a German Jesuit mathematician and astronomer, first noticed sunspots in 1611 and later reported them through letters published under the pseudonym “Apelles.”

Galileo responded with Letters on Sunspots, published in 1613. He argued that sunspots were features on or very near the Sun’s surface, carried around as the Sun rotated. Scheiner initially proposed that they might be small bodies or planets passing in front of the Sun, although his later work moved closer to Galileo’s interpretation.

Their disagreement was not simply about what sunspots were. Both men also competed for recognition, and each accused the other of claiming discoveries unfairly. Galileo’s polemical style made the quarrel especially severe. The dispute is sometimes linked to the hostility Galileo later faced, but Scheiner’s direct influence on the 1633 trial cannot be proved. Other early observers, including Chinese astronomers and European astronomers such as Johannes Fabricius, had also seen sunspots, so “observed at the same time” does not mean Scheiner was the first person ever to notice them.