Wikipedia
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. It is named in honour of the American physicist Marcus O'Day.
The crater rim of O'Day remains sharp-edged, and the inner wall is terraced, especially in the northwestern half away from the mare. 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 midpoint.
Due to its prominent rays, O'Day is mapped as part of the Copernican System.
O'Day is a surname of Irish origin. Notable people with the surname include:
- Alan O'Day (1940–2013), American singer-songwriter
- Anita O'Day (1919–2006), American jazz singer
- Aubrey O'Day (born 1984), American singer, dancer, actress, songwriter, fashion designer, former member of the group Danity Kane
- Caroline Love Goodwin O'Day (1875–1943), American politician
- Constance O'Day-Flannery, an American author of romance novels
- Daniel O'Day, one of northwestern Pennsylvania's earliest independent refiners to be brought into John D. Rockefeller's Standard Oil Company
- Darren O'Day (born 1982), Major League Baseball relief pitcher for the Baltimore Orioles
- Devon O'Day (born 1962), American radio personality, former plus-sized model for the Ford Modeling Agency, songwriter, and an author
- George O'Day (1923–1987), American sailor, Olympic champion and boat designer
- Hank O'Day (1859–1935), American right-handed pitcher, umpire and manager in Major League Baseball
- Jeremy O'Day (born 1974), offensive lineman for the Saskatchewan Roughriders of the Canadian Football League
- Marcus O'Day (1897–1961), American physicist
- Molly O'Day (1911–1998), American film actress
- Molly O'Day (singer) (1923–1987), American country music vocalist in the late 1940s
- Nell O'Day (1909–1989), accomplished equestrian and B-movie actress of the 1930s and 1940s
- Pat O'Day (born 1934), Pacific Northwest broadcaster and promoter