Countdown

The countdown ( rare: Countdown ) (English " count down ", " count-back " ) is clocked ( just before the end of every second) announcement of up to a specified event (eg launch of a missile, year etc. ) missing time. Is specified Formally, the time of the event in rocket launches, for example with T ( take-off ), the. Still missing period t ( eg 10 min), so that announcements such as arise "T minus 10 minutes " In general, the countdown is stopped and performed according counted just before the start during the last seconds.

Formation

The countdown was first staged in the science fiction silent film Woman in the Moon (1929 ) by Fritz Lang to increase the drama about to take off the moon rocket shown.

Countdown for launch in space

The countdown there is almost always at rocket launches, where before the starting process - numerous checks for a statutory plan shall be placed in a narrow window of time - especially in liquid rockets. The critical tests must be completed successfully at a certain time before take-off the rocket here, otherwise this leads to the continuation or termination of the countdown.

Depending on the complexity of the start of the countdown starts a few minutes (start small ballistic missiles ) to 7 days ( launches manned ) prior to the scheduled start time T.

If a heavier problem, the countdown is interrupted to correct it. If the problem is not fix (Splash ) within the specified time, the countdown is canceled and postponed the start. At the start of the space shuttles have fixed times when the countdown was stopped in order to work, which had taken longer than expected to complete, can. Only when this work was completed, he continued, or if by the end of the launch window was not possible aborted. The last scheduled stop before the start was -9 minutes at T.

The last seconds of the countdown are often counted down aloud: 10 - 9 - 8 ... 3 - 2 - 1 - Zero ( also Go or ( Ignition ... and) lift-off ). Even with television broadcasts of control centers, this has become common. In launches from Kourou Space Center, the countdown will be announced in the French language ( " ... trois - deux - unité or un - top or feu "), as Kourou is located in French Guiana. This does not mean the zero point of the lifting, as with the U.S. launch, but the ignition of the engines.

The count down is only typical of the western world, launch Russian missiles without loud countdown.

Others use

Before large social events such as the Football World Cup or the beginning of a new year New Year's Eve, are also found in numerous internet countdown timer that counts down the time until the start. Countdown timer that counts down the time to a personal event, can be created at various sites on the Internet.

Some watches, especially digital watches, contain a Countdown. In this case an alarm is triggered after the expiry of the selected time period.