Which Dutch astronomer discovered Saturn's moon Titan in 1655?

Christiaan Huygens discovered Saturn’s moon Titan in 1655.

The Dutch astronomer made the discovery on 25 March 1655 using a refracting telescope he helped construct with his brother Constantijn. Titan was the first moon known to orbit Saturn and became the sixth planetary satellite identified after Earth’s Moon and Jupiter’s four Galilean moons.

Huygens initially described it as Saturn’s moon rather than giving it the name Titan. The mythological name was introduced later by John Herschel in 1847; Titan refers to the powerful beings of Greek mythology. The moon is officially designated Saturn VI.

Titan is far more than a historical discovery. It is larger than Mercury, has a dense nitrogen-rich atmosphere, and contains lakes and seas of liquid methane and ethane. NASA’s Cassini spacecraft and ESA’s Huygens probe revealed a world with weather, rivers, dunes, and shorelines.