At 5:21 p.m. on July 19, Apollo 11 arrived at the moon. Entering lunar orbit, Aldrin and Armstrong spent the next few hours checking the lunar module, named Eagle. Then they ate dinner and got some rest. Around 9:30 a.m. the next morning, Aldrin and Armstrong suited up, entered Eagle and sealed the hatch. An hour later the radio sounded with the crackly voice of mission control: “Apollo 11, Houston. We’re go for undocking.” Inside the mothership, Collins flipped a switch. The Eagle detached, and the two ships drifted apart. Armstrong released Eagle’s landing gear, and he and Aldrin began running through an extensive preparatory checklist. Next, they needed to start the engines that would power their descent. The engine burn had to be exactly 28.5 seconds – any longer, and it would send them hurtling toward the moon at deadly speed. But it went perfectly, and lowered Eagle just enough for the moon’s gravity to seize it and slowly pull it down. Since the moon has no atmosphere, and gravity there is just 16 percent that of Earth’s, they didn’t have to worry about a blisteringly hot and fast entry. Five minutes into the descent, several alarms began to sound. The onboard computer showed alarm code 1201. Armstrong and Aldrin looked at each other; neither knew about this alarm. But half a minute later, mission control told them it was safe to continue. The alarms indicated that the onboard computer was being overloaded with tasks. After a restart, it would continue with only the most essential calculations. They were still on for a moon landing. With Aldrin reading out crucial data, like speed of descent and altitude, Armstrong took manual control of the lunar module as planned and slowed the descent to 13 miles per hour. When they were 60 feet from the surface, a cloud of dust kicked up, obscuring their vision; Armstrong could barely judge where the ground was. Neither astronaut felt the touchdown, but they had suddenly stopped moving. But they didn’t just suit up and go outside – there was work to do. The astronauts simulated a countdown for the next day’s liftoff, and ran through a number of other launch procedures. After this, the schedule called for them to rest, because NASA assumed they’d be mentally and physically exhausted after lunar descent. But they weren’t. They radioed Houston, and requested permission to go outside early. Houston agreed.