The Impossible Astronaut was first transmitted 23 April, 2011. It was dedicated to one of the greats of Doctor Who, Elisabeth Sladen, who passed away four days earlier.

All recent seasons of Doctor Who have begun with a one-part adventure. In fact, this is the first two-part story to open a season since Attack of the Cybermen in 1985.

The read through for The Impossible Astronaut took place at Upper Boat, Wales on Friday, 8 October, 2010.

When Canton is still reeling after learning some of the secrets of the TARDIS, the Doctor says to him, 'Brave heart, Canton!' The Fifth Doctor used to encourage and reassure Tegan Jovanka with the words 'brave heart' and moments before he regenerated, the Fifth Doctor had a vision of his former companion quoting the phrase back to him.

This is the first time that Doctor Who has featured extensive shooting in the USA. Steven Moffat (Lead Writer and Executive Producer) announced the news in 2010, saying 'The Doctor has visited every weird and wonderful planet you can imagine, so he was bound get round to America eventually! And of course every Doctor Who fan will be jumping up and down and saying he's been in America before. But not for real, not on location - and not with a story like this one! Oh, you wait!'

Nixon is not the first President we've seen on Doctor Who. Abraham Lincoln appeared in the First Doctor adventure, The Chase and at the beginning of Remembrance of the Daleks we catch a tiny fragment of one of President John F Kennedy's speeches. Later, Clive Finch, who had made it his life's work to seek out the Doctor, showed Rose Tyler a photo of JFK... the Time Lord was clearly visible in the background.

Stuart Milligan plays Richard Nixon in The Impossible Astronaut. He's no stranger to the world of Doctor Who and starred as Colonel Stark in the animated adventure, Dreamland. You can watch an interview with Stuart and learn more about his role in Dreamland here.

The notion of an invisible TARDIS is not entirely new... Back in the early 1960s when the concept of Doctor Who was being fleshed out by the BBC, two of the programme's initial creative forces, Cecil Edwin Webber and Sydney Newman, wrote a four-page outline for the show. Their intention for the Doctor's craft was clear: '...we do not see the machine at all; or rather it is visible only as an absence of visibility... (the Doctor) has achieved this 'disappearance' by covering the outside with light resistant paint...' The document went on to say, 'characters can bump into it' (meaning the machine). It would be almost half a century before the Doctor does just that, colliding with his 'cloaked' TARDIS in the Oval office.

Despite his disappointment in this episode, the Doctor has tried wine in the past. The Fourth Doctor unwittingly sipped poisoned wine in The Brain of Morbius and the Third Doctor found a particular wine to his taste in Day of the Daleks, extolling its virtues and declaring it was '...a touch sardonic perhaps, but not cynical'.

In The Talons of Weng-Chiang, one of the Doctor's friends mistakenly declares that the Time Lord must help out Scotland Yard, but here it's the Doctor himself who implies he works for the world-famous organisation. Scotland Yard is an unofficial name for the Metropolitan Police Service of London, derived due to the original Met having an office with a rear entrance leading to Great Scotland Yard, Westminster.

Amy swears on fish fingers and custard - a reference to the meal that the Doctor devoured when they first met in The Eleventh Hour.

The old movie that the Doctor becomes a part of is The Flying Deuces (1939) directed by A. Edward Sutherland. It stars Stan Laurel and Oliver Hardy and the Doctor's intervention comes as the comic duo is dancing to Shine on Harvest Moon.

The Doctor's teasing reference to Mrs Robinson alludes to the character played by Anne Bancroft in The Graduate (1967), directed by Mike Nichols. She's a character who's attracted to a much younger man - hence River's reaction! We never learn Mrs Robinson's first name, either in the movie or the book it's based on: The Graduate (1963) by Charles Webb.