In 1969 America, alien time traveller the Doctor (Matt Smith) along with his companions Amy Pond (Karen Gillan) and Rory Williams (Arthur Darvill), archaeologist River Song (Alex Kingston) and FBI agent Canton Everett Delaware III (Mark Sheppard), attempt to lead the human race into a revolution against the Silence, a religious order of aliens who cannot be remembered after they are encountered.

"The Impossible Astronaut" and "Day of the Moon" were designed to be a darker opener to the series and were partially filmed in the United States, a first for the programme.

Moffat was keen on incorporating Area 51, the Apollo 11 Moon landing, and President Richard Nixon (played by Stuart Milligan) into the plot.

The Eleventh Doctor and his allies, Amy, Rory, River Song and ex-FBI agent Canton Everett Delaware III, escape the girl in the space suit, and spend three months tracking down the alien religious order the Silence and find they exist across the entire planet, and have the ability to place post-hypnotic suggestions in humans they encounter.

While the Doctor alters part of the Command Module Columbia of Apollo 11, Canton and Amy visit a nearby orphanage in Florida, hoping to find where the girl in the space suit was taken from.

As they watch, the Doctor uses his modification of the Apollo command module Columbia to insert Canton's recording of the wounded Silence member into the footage of the landing.

[10] Director Toby Haynes believed that the darker episodes like "The Impossible Astronaut" and "Day of the Moon" would allow the series to get into "more dangerous territory.

Elsewhere in the episode, Delaware was written to be deceptively antagonistic towards the protagonists, which was based on actor Mark Sheppard's past as villains for his work in American television.

[11] Incorporating Nixon into the plot was accidental; Moffat wanted to set the story during the Moon landing and looked up the United States president during the time.

[2] "The Impossible Astronaut" and "Day of the Moon" marked the first time that Doctor Who has filmed principal photography footage within the United States.

To add the effect that a storm is outside the building, the production crew placed rain machines outdoors and flashing lights to simulate lightning.

Dan Martin of The Guardian praised the episode for its "action, tension, horror and River Song in a business suit," but felt it "sags a little around the middle.

[20] Morgan Jeffery of Digital Spy stated "after the sensational opening gambit that kicked off the series premiere, it's perhaps unsurprising that 'Day of the Moon' starts with a similarly thrilling onslaught of action.

"[21] Jeffery was positive towards the nano-recorder, which provided the episode with "a number of unsettling moments in which characters listen back to their own terrified exclamations about the Silents.

[21] Tom Phillips of Metro stated that "Amy and Canton's sojourn to the orphanage was not just a high-mark for sheer skin-crawling horror on recent mainstream telly — that image of The Silence nesting on the ceiling like cadaverous bat-people will live on in the nightmares of many, many children — but also genuinely, properly weird.

"[23] Golder went on to state that "once again we're treated to some outstanding direction, glorious performances, near flawless FX and gorgeous locations ... "Day Of The Moon" is huge fun, effortlessly entertaining, beguilingly bat's-arse and blessed with a cliffhanger so jawdroppingly unexpected it's bound to keep viewers hooked".

"[24] When comparing it to "The Impossible Astronaut", he said it was "scarier, creepier...and more action packed in every way...[and] also managed to leave things on a suitably epic, mythos-expanding note.

"[25] Fuller believed that the plot and ending "only raised more questions than answers," believing that the overarching storyline would "require the audience's concentration over many weeks; any casual viewer tuning in this week, and I suspect not a few fans, will have been left baffled by the goings-on," but still felt the episode "was interesting and showed just how, when the writers use their imagination, Doctor Who can tell stories in a way little else on television can.