Thomson is a lunar

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 crater

Impact crater

In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

 that is located within the Mare Ingenii

Mare Ingenii

Mare Ingenii is one of the few lunar mare features on the far side of the Moon. The mare sits in the Ingenii basin. This basin material is of the Pre-Nectarian epoch. The mare material located in Ingenii and the surrounding craters is of the Upper Imbrian epoch...

 on the far side of the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. Just to the northeast is the unusual merged crater formation of Van de Graaff

Van de Graaff (crater)

Van de Graaff is an unusual lunar formation that has the appearance of two merged craters, approximately in a figure-8 shape with no intervening rim separating the two halves. The crater is located on the far side of the Moon, on the northeast edge of Mare Ingenii. The crater Birkeland is attached...

. On the northwest rim of the mare

Lunar mare

The lunar maria are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas. They are less reflective than the "highlands" as a result of their iron-rich compositions, and...

 is O'Day

O'Day (crater)

O'Day is a prominent lunar impact crater that is located on the far side of the Moon. It intrudes into the northwestern edge of Mare Ingenii, and the rim is lower on that side. To the northwest is the crater pair of Holetschek and Sierpinski. Southwest of O'Day lies the crater Seidel...

, and to the south-southwest is Obruchev

Obruchev (crater)

Obruchev is a disintegrating lunar crater that lies along the southern shore of Mare Ingenii, on the far side of the Moon. Less than three crater diameters to the south of Obruchev is the crater Chrétien, and about the same distance to the southeast lies Oresme.The outer rim of this crater has been...

 on the southern shore of Mare Ingenii.

In the past the crater was flooded by lava

Lava

Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

, leaving only the outer rim intact. There are gaps in the eastern and western rims, leaving two "half-moon" mountainous formations facing each other across the relatively flat floor. There is a similar lava-flooded crater remnant attached to the southern rim of Thomson. The floor of Thomson has a number of secondary impacts that form short, linear streaks across the surface.

Satellite craters

By convention these features are identified on lunar maps by placing the letter on the side of the crater mid-point that is closest to Thomson.

Thomson	Latitude	Longitude	Diameter
J	35.9° S	169.6° E	44 km
M	35.7° S	166.0° E	119 km
V	30.7° S	162.2° E	13 km
W	30.2° S	163.3° E	17 km