Mare Tranquillitatis

8.5°N, 31.5°E

Mare Tranquillitatis, the ‘Sea of Tranquillity’, is an area of about 420 000 km2, slightly larger than Mare Serenitatis that lies to its north. Its size is comparable with the Black Sea on Earth. Like all the maria, Tranquillitatis is also the central, lava-flooded region of a considerably larger impact basin, and associated with a gravitational anomaly a mascon).

The enormous lava expanse of Mare Tranquillitatis was the target of some unmanned lunar probes: Ranger 6, Ranger 8 (1965, hard landings) and Surveyor 5 (1967, soft landing). Ranger 6 was a failure, because the cameras could not be activated shortly before impact. In 1969 the first manned lunar landing with Apollo 11 took place in the southern portion of the mare. The landing site of the landing module Eagle lay near to Ranger 8 and Surveyor 5, east of the craters Ritter and Sabine.

Mare Tranquillitatis offers a whole range of extremely interesting lunar formations for both small and large telescopes. The graduated brightness of the lava boundary southwest of the crater Carrel is remarkable, as is the lava boundary between Mare Serenitatis and Mare Tranquillitatis, north of the crater Plinius; the formation Lamont in the southwestern portion of Tranquillitatis is unique on the Moon's nearside; the lunar domes near Arago; the region around Cauchy and Jansen; and the broad rille systems on the western border of Tranquillitatis: Rimae Hypatia, Ritter, Sosigenes, and Maclear.