A countdown is the backward counting to indicate the seconds, days, etc. remaining before an event. Typical events for which a countdown is used include the launch of a space rocket, the explosion of a bomb, the start of a race or New Year. A Redstone rocket, part of the Mercury program A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust gas from within a rocket engine. ... This article is about explosive devices. ... Offshore inflatable racing (Thundercat class) at Ilfracombe, north Devon, England. ... This page deals with the annual event. ...

In the context of a rocket launch, the "T minus Time" is the time before launch, e.g. "The countdown was held at T minus 5 minutes for 3 minutes and 40 seconds". The last ten seconds are usually counted down aloud "10, 9, 8, 7, 6, 5, 4, 3, 2, 1, Lift off!"

The first known use with respect to launching a rocket occurred in Fritz Lang's 1929 film Frau im Mond. In the film, after each number the words "seconds to go" was repeated. Friedrich Anton Christian Lang (December 5, 1890 - August 2, 1976) was an Austrian film director, screenwriter and occasional film producer, one of the most famous emigrés from Germanys school of expressionism to work in Hollywood. ... 1929 was a common year starting on Tuesday (link will take you to calendar). ... Film refers to the celluloid media on which movies are printed Film — also called movies, the cinema, the silver screen, moving pictures, photoplays, picture shows, flicks, or motion pictures, — is a field that encompasses motion pictures as an art form or as part of the entertainment industry. ... Frau im Mond is a science fiction movie released in 1929, and is often considered to be one of the first serious science fiction films. ...

The countdown is a inverse counting from a certain bigger number to a smaller one. Often this countdown starts at a bigger number until zero, but sometimes the countdown stops before reaching zero.

Numbers in mathematics A number is an abstract entity used originally to describe quantity. ...

External links

• Free and simple JavaScript countdown timer (http://www.hashemian.com/tools/countdown.htm)