A countdown is the backward counting to indicate the seconds, days, etc. remaining before an event occurs or a deadline expires. Typical events for which a countdown is used include the launch of a rocket or spacecraft, the explosion of a bomb, the start of a race, or the New Year. A rocket or rocket vehicle is a Missile, Aircraft or other Vehicle which obtains Thrust by the reaction of the A spacecraft is a Vehicle or machine designed for Spaceflight. A bomb is any of a range of devices that typically rely on the Exothermic Chemical reaction of an Explosive material to produce an extremely Types of racing Unassisted human racing Using only the Human body 's own Muscles Running: Cross country The New Year is an event that happens when a Culture celebrates the end of one Year and the beginning of the next year

Rocketry

Seven seconds after launch of STS-121, the countdown clock on the grounds of the Kennedy Space Center News Center is counting up, rather than down. STS-121 was a space shuttle mission to the International Space Station (ISS flown by Space Shuttle '' Discovery''. The Press Site-Clock and Flag Pole is a historic site on Merritt Island, Florida. The John F Kennedy Space Center ( KSC) is the NASA Space vehicle launch facility and Launch Control Center ( Spaceport) on

In the context of a rocket launch, the "T minus Time" is the time before launch, e. g. "T minus 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!" After a launch, most countdown clocks begin to show Mission Elapsed Time.

The first known use with respect to launching a rocket occurred in Fritz Lang's 1929 film Frau im Mond. Friedrich Christian Anton "Fritz" Lang ( December 5, 1890 &ndash August 2, 1976) was an Austrian German - American Year 1929 ( MCMXXIX) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar. In the film, after each number the words "seconds to go" was repeated.

When counting down to the launch of an explosive, e. An explosive material is a material that either is chemically or otherwise Energetically unstable or produces a sudden expansion of the material usually accompanied g. when testing a new model of gun, it is customary to omit "5" from the countdown sequence because "five" sounds too similar to "Fire!".

Film

At the start of films, a countdown sequence is printed on the head leader, to aid in synchronizing the film. A film leader is a length of film attached to the head or tail of a film to assist in threading a Projector or Telecine.

The countdown ends just as "two" is displayed so that the countdown isn't shown if the film is put on screen a little earlier than intended. Although this sequence was usually not intended for broadcast, being a cue device for a projectionist or TV producer, it is sometimes used in modern-day spoofs to signify old film footage. A parody (ˈpɛɹədiː US, [ˈpaɹədiː] UK) in contemporary usage is a work created to mock comment on or poke fun at an original work its subject

New Year's Eve

Main article: New Year's Eve

Taipei 101 New Year's fireworks and countdown, 2008

In many New Year's Eve celebrations, there is a countdown during the last seconds of the old year until the beginning of the new year. New Year's Eve is on December 31, the final day of the Gregorian year and the day before New Year's Day. Taipei 101 ( POJ: Tai-pak yat-leng-yat is a 101-floor Landmark Skyscraper located in Xinyi District, Taipei, Taiwan The New Year is an event that happens when a Culture celebrates the end of one Year and the beginning of the next year A firework is classified as a low explosive pyrotechnic device used primarily for aesthetic and entertainment purposes New Year's Eve is on December 31, the final day of the Gregorian year and the day before New Year's Day. Additionally, countdowns are often used to count down the days before special events, such as major holidays and one's birthday.

External links

• NASA Countdown 101
• Countdown Clocks Software