#firmicus

Mare Crisium, the Sea of Crises, was the site of a crash-landing of Soviet Luna 15 in 1969, and soft-landing of Luna 24 in 1976.

Cleomedes crater is named after the Greek astronomer Cleomedes (dates unknown), who wrote a textbook containing the original source for how Eratosthenes measured the Earth’s circumference to within 2%.

Firmicus crater is named after the Roman astrologer Julius Firmicus Maternus (c. 300s CE).

Petavius crater is named after the French Jesuit Denis Pétau (1583-1652) known for his works on chronology.

Balmer crater is named after the Swiss mathematician Johann Balmer (1825-1898) who studied the hydrogen atom, discovering its series of optical emission lines.

Langrenus crater is named after the Dutch astronomer Michael van Langren (1598-1675) who used observations of the Moon to help determine longitude on Earth.

Apollonius crater is named after Apollonius of Perga (c. 240 BC - 190 BC), an ancient Greek astronomer who defined the terms ellipse, parabola, and hyperbola, and introduced eccentric orbits for the planets.