21 December

In the southern hemisphere on Earth, 21 December was also known as Midsummer's Eve. (PROSE: Iceberg) In the northern hemisphere, it was instead the winter solstice. While John Lennon was convinced that the date was also Aztec sun god Huitzilopochtli's birthday, the Seventh Doctor dismissed him as "getting [his] mythologies meddled". (PROSE: The Left-Handed Hummingbird)

In 1981, the Hecate Cult intended to sacrifice Brendan Richards in Moreton Harwood. However, he was rescued by Sarah Jane Smith and K9 Mark III before this could happen. (TV: A Girl's Best Friend)

In 2010, it was also the date of an unknown Torchwood Three operation. The date was in both Captain Jack Harkness' and Gwen Cooper's CIA files, detailing the figures of a "case" numbered "00938478766-04". (TV: The New World)