The "Blue Peter" referred to in the title is a flag flown by Royal Navy ships to indicate they are about to leave port. It is a blue flag with a white square in the center. The same flag also stands for the letter "P" in the international flag signal alphabet.
The series was used by the BBC as a platform to launch several upcoming programs aimed at children, in particular Doctor Who (1963). Long-running presenter Peter Purves had played a companion to William Hartnell's Doctor before joining Blue Peter and Janet Ellis had also acted in a Doctor Who serial starring Tom Baker before joining as a presenter.
The title music is called "Barnacle Bill", composed by Herbert Ashworth-Hope. The original "classic" version, used from October 1958 to January 1979, was played by Sidney Torch and The New Century Orchestra.
The show has two time-capsules still to be opened: one was interred at BBC TV Centre in 2000 for excavation in 2029 and contains the then-current 29th Blue Peter Book and team details, instructions to make a George the tortoise toy, VHS and DigiBeta programme highlights, a 40th anniversary gold medallion and set of badges, a CD from Konnie Huq, Simon Thomas' old mobile phone, a ring from Katy Hill's Mongolian trip, and a Geordie phrasebook from Matt Baker). In February 2012 this (along with the bust of Petra and Italian sunken garden) was moved to MediaCityUK in Salford, Manchester when production relocated there from London. The second was placed at the Greenwich Millennium Dome site on 11th June 1998, for recovery in 2050. Contents include a Blue Peter badge and series history, plus viewers suggestions such as Teletubby dolls, a France '98 football and an insulin pen.
Of the period 16th October 1958 to 5th November 1962, only two clips from the show are known to be archived. Approximately 312 editions survive from between 12 November 1962 and 9th December 1968, whilst (thanks to long-term series editor Biddy Baxter) every episode exists from Thursday 12th December 1968 onwards.
Main-belt Asteroid 16197 is named "Bluepeter" as it was discovered on Friday 7th January 2000 - the day that footage of the excavation of the shows' two time-capsules (from 1971 and 1984) in the BBC Television Centre garden was broadcast.
The trivia item below may give away important plot points.
On one episode in May 2016, the presenters were given a pie to pie their faces with. Radzi did, but Lindsey tried to run away. The credits played over Lindsey running away so we did not see whether she pied her face or not.