Expressions (phrases, clauses, etc.), Noun
1. Mare Tranquillitatis (lunar mare); Sea of TranquilityAstronomy
Wikipedia definition
2. Mare TranquillitatisMare Tranquillitatis (Latin for Sea of Tranquility) is a lunar mare that sits within the Tranquillitatis basin on the Moon. The mare material within the basin consists of basalt formed in the intermediate to young age group of the Upper Imbrian epoch. The surrounding mountains are thought to be of the Lower Imbrian epoch, but the actual basin is probably Pre-Nectarian. The basin has irregular margins and lacks a defined multiple-ringed structure.
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