15 November

On 15 November 1966, Perpugilliam "Peri" Brown, companion to the Fifth and Sixth Doctors, was born. (AUDIO: Peri and the Piscon Paradox)

In 1807, Mannering Caversham died. (AUDIO: The Darkness of Glass)

In 1859, there were exactly 1,000,300,558 humans on Earth. (AUDIO: The Pursuit of History)

Behind the scenes
Peri's birthday in Peri and the Piscon Paradox is a likely reference to a production error in Planet of Fire where Peri's passport was actually made for another production. As such, her name is listed as Sydney and her birthdate is listed as 15 November 1940.