Dionysius 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...

 impact 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 lies on the western edge of the Mare Tranquillitatis

Mare Tranquillitatis

Mare Tranquillitatis 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...

. To the southeast is the crater pair of Ritter

Ritter (crater)

Ritter is a lunar crater located near the southwestern edge of Mare Tranquillitatis. It is the northwestern member of a crater pair with Sabine to the southeast. The two rims are separated by a narrow valley only a couple of kilometers wide. To the northwest is the crater Dionysius, and to the...

 and Sabine

Sabine (crater)

Sabine is a lunar crater that forms a nearly matching pair with Ritter to the northwest. The two rims are separated by a distance of only a couple of kilometers. To the west is the bowl-shaped crater Schmidt, and farther to the north are Manners and Arago....

. Just to the northwest is the system of rille

Rille

Rille is typically used to describe any of the long, narrow depressions in the lunar surface that resemble channels. Typically a rille can be up to several kilometers wide and hundreds of kilometers in length...

s designated Rimae Ritter. These clefts follow a generally northwest direction.

The rim of Dionysius is generally circular and shows little sign of wear. The crater possesses a small ray system

Ray system

A ray system comprises radial streaks of fine ejecta thrown out during the formation of an impact crater, looking a bit like many thin spokes coming from the hub of a wheel. The rays can extend for lengths up to several times the diameter of their originating crater, and are often accompanied by...

 with a radius of over 130 kilometers. The formation has a high albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

and appears bright when the Sun is nearly overhead during a full Moon. It is surrounded by a bright halo, with darker material farther out. Some darker deposits are in the form of relatively rare dark rays.

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 Dionysius.

Dionysius	Latitude	Longitude	Diameter
A	1.7° N	17.6° E	3 km
B	3.0° N	15.8° E	4 km