A launch countdown includes “L Minus” to indicate how far away liftoff is in hours and minutes, and “T Minus” to show a sequence of events built into the launch countdown.

NASA’s long-awaited Artemis II mission marks the first crewed journey to orbit the moon since 1972.

If all goes according to plan, the crew — commander Reid Wiseman, pilot Victor Glover, and mission specialists Christina Koch and Jeremy Hansen — will get an unprecedented view of the far side of the ...