Mare Tranquillitatis
Type: Lunar Sea
Size: 700x700km
Longitude/latitude: 30.8° E, 8.3° N
Age: Older than 3.9 billion years
Best time to see: Five days after new Moon (21-24 July) or four days after full Moon (7-9 July)
Minimum equipment: Naked eye
Fifty-four years ago, or more precisely on 21 July 1969, Neil Armstrong was the first human to set the Sea of Tranquillity. From Earth, it's one of the defining dark regions of the Moon's familiar face, the central sea of three dark patches in a row, with 650km to the northwest and 350km to the southeast. All three are visible as distinct features to the unaided eye. In angular terms, Serenitatis appears 349 arcseconds, Tranquillitatis 376 arcseconds and Nectaris 188 arcseconds across. The eye can't resolve features smaller than 60 arcseconds. The distinctive and non-joined (620km x 570km, 333 arcseconds) appears immediately east and slightly north of Mare Tranquillitatis.
