O'Day is a prominent 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 is located 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...

. It intrudes into the northwestern edge of 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...

, and the rim is lower on that side. To the northwest is the crater pair of Holetschek

Holetschek (crater)

Holetschek is a lunar crater on the far side of the Moon, to the south-southeast of the huge walled plain Gagarin. To the east of Holetschek is the crater Sierpinski. To the west-southwest is the larger satellite crater Holetschek R....

 and Sierpinski

Sierpinski (crater)

Sierpinski is a lunar impact crater on the far side of the Moon. It lies to the southeast of the huge walled plain Gagarin, and to the northwest of the crater O'Day and the Mare Ingenii....

. Southwest of O'Day lies the crater Seidel

Seidel (crater)

Seidel is a worn lunar impact crater that lies to the east-northeast of the much larger crater Jules Verne. Farther to the east of Seidel is the western edge of Mare Ingenii, and to the northeast lies the crater O'Day....

. It is named in honour of the American physicist Marcus O'Day

Marcus O'Day

Marcus Driver O'Day was an American physicist.In 1918, he entered the military service in Eugene, Oregon after graduating from Centralia, Washington. He then attended the University of Oregon where he was assigned to the Students Army Training Corps, and was discharged at the end of the...

.

The crater rim of O'Day remains sharp-edged, and the inner wall is terraced, especially in the northwestern half away from 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...

. A small crater lies across the southern rim, and a tiny craterlet is located in the low inner rim between the crater and the mare. The floor is rough and irregular, with a double-peak at the mid-point.

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 O'Day.

O'Day	Latitude	Longitude	Diameter
B	29.1° S	158.0° E	16 km
M	31.7° S	157.1° E	16 km
T	30.4° S	154.4° E	24 km

External links

• Large views of O'Day and lunar surroundings. (Regional maps at the Lunar and Planetary Institute
  Lunar and Planetary Institute
  The Lunar and Planetary Institute is a scientific research institute dedicated to study of the solar system, its formation, evolution, and current state. The Institute is part of the Universities Space Research Association and is supported by the Science Mission Directorate of the National...
  
  .)