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Listen to the final countdown of Apollo 11
A countdown is the step-by-step process leading to a launch. It runs according to a prearranged schedule, measured in terms of T-time (T minus time before the engine start sequence begins and T plus time thereafter). T-0:00:00 is not necessarily the liftoff point, however; the Space Shuttle, for example, typically lifts off at T+0:00:03.

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