The landing on the surface of the Moon occurred several seconds after 20:17:40 UTC on July 20, 1969. One of three probes attached to three of the LM's four legs made contact with the surface, a panel light in the LM illuminated, and Aldrin called out, "Contact light." Armstrong shut the engine off and said, "Shutdown." As the LM settled onto the surface, Aldrin said, "Okay, engine stop"; then they both called out some post-landing checklist items. After a 10-second pause, Duke acknowledged the landing with, "We copy you down, "Eagle"." Armstrong announced the landing to Mission Control and the world with the words, "Houston, Tranquility Base here. The "Eagle" has landed." Aldrin and Armstrong celebrated with a brisk handshake and pat on the back. They then returned to the checklist of contingency tasks, should an emergency liftoff become necessary. After Armstrong confirmed touch down, Duke re-acknowledged, adding a comment about the flight crew's relief: "Roger, Tranquility. We copy you on the ground. You got a bunch of guys about to turn blue. We're breathing again. Thanks a lot." During the landing, Armstrong's heart rate ranged from 100 to 150beats per minute.