Sea / bay

Mare Tranquillitatis

The Sea of Tranquility is an irregular dark plain in the eastern near side, known as the region of the Apollo 11 landing.

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Mare Tranquillitatis and surrounding lunar terrain in the LROC Wide Angle Camera mosaic
Mare Tranquillitatis · North up, east right. Open image ↗
NASA / GSFC / Arizona State University · LROC WAC mosaic via USGS. Regional map crop; lighting is fixed and does not follow the selected date.
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How to observe Mare Tranquillitatis

Follow its connections to neighbouring maria. The landing region can be located, but spacecraft hardware cannot be resolved with a backyard telescope.

Finding the region

Look at 8.35° N, 30.83° E on the lunar disc. The chart marker identifies the catalogue centre. Start with a wide field and use the nearby formations below as landmarks.

Equipment & conditions

These dark plains are a good starting point with binoculars. Trace their shapes at low power, then examine the boundary with the brighter highlands. Higher sunlight helps reveal brightness differences; low sunlight brings out ridges.

Lighting

For surface relief, try a time when the Sun is low over this region. To compare surface brightness and any bright rays, return under higher illumination. The atlas calculates the solar elevation at the formation’s centre for any selected date.

View Mare Tranquillitatis in the atlas

IAU / USGS Gazetteer

Official feature record

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Approved name
Mare Tranquillitatis
Feature classification
Mare, maria
Catalogue dimension / extent
875.75 km
Centre latitude
8.35° N
Centre longitude
30.83° E
Name origin (Gazetteer)
"Sea of Tranquility."

Coordinates are selenographic, with east-positive longitude. Dimensions are the Gazetteer’s catalogue values; for extended formations they do not represent a circular crater diameter. Data snapshot: 2026-09-16. Observing guidance above is separate from the official record.

Nearby formations

The four closest catalogue entries, measured from their centres.

LROC photograph of TheophilusImpact crater

Theophilus

The northern member of the Theophilus–Cyrillus–Catharina group beside Mare Nectaris. Its prominent central mountains contrast with its older-looking neighbours.

LROC photograph of Mare SerenitatisSea / bay

Mare Serenitatis

The Sea of Serenity is a rounded dark plain in the northern near side. Its shape is easy to recognise among the connected lunar maria.

LROC photograph of CyrillusImpact crater

Cyrillus

A worn crater beside Mare Nectaris, partly overlapped by Theophilus. The adjoining rims illustrate how later impacts reshape older terrain.

LROC photograph of PosidoniusImpact crater

Posidonius

A large crater on the northeastern margin of Mare Serenitatis. Its fractured floor is easier to distinguish under low sunlight.