Apollo 13's Wristwatch Burn: Navigating Home by the Terminator Line

Facing a life-or-death power budget after Apollo 13's oxygen-tank explosion, the crew shut down nonessential systems, used the Aquarius lunar module as a lifeboat, and manually performed a 14-second trajectory burn by aligning Earth's terminator in the LM window and timing it with Swigert’s Omega Speedmaster—an improvised navigation method that ensured a splashdown and became a lasting NASA contingency lesson.