"Day of the Moon" is the second episode of the sixth series of the British science fiction television series Doctor Who. Written by show runner Steven Moffat, and directed by Toby Haynes, the episode was first broadcast on 30 April 2011 on BBC One in the United Kingdom and on BBC America in the United States. The episode is the second of a two-part story that began with "The Impossible Astronaut" on 23 April.

The sixth series of British science fiction television programme Doctor Who was shown in two parts. The first seven episodes were broadcast from April to June 2011, beginning with "The Impossible Astronaut" and ending with mid-series finale "A Good Man Goes to War". The final six episodes aired from August to October, beginning with "Let's Kill Hitler" and ending with "The Wedding of River Song". The main series was preceded by "A Christmas Carol", the 2010 Christmas special. The series was led by head writer and executive producer Steven Moffat, alongside executive producers Beth Willis and Piers Wenger. Sanne Wohlenberg, Marcus Wilson, and Denise Paul served as producers. The series was the sixth to air following the programme's revival in 2005 after the classic era aired between 1963 and 1989, and is the thirty-second season overall.