<P> On July 19 at 17: 21: 50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit . In the thirty orbits that followed, the crew saw passing views of their landing site in the southern Sea of Tranquility (Mare Tranquillitatis) about 12 miles (19 km) southwest of the crater Sabine D (0.67408 N, 23.47297 E). The landing site was selected in part because it had been characterized as relatively flat and smooth by the automated Ranger 8 and Surveyor 5 landers along with the Lunar Orbiter mapping spacecraft and unlikely to present major landing or extravehicular activity (EVA) challenges . </P> <P> On July 20, 1969, the Lunar Module Eagle separated from the Command Module Columbia . Collins, alone aboard Columbia, inspected Eagle as it pirouetted before him to ensure the craft was not damaged . </P> <P> As the descent began, Armstrong and Aldrin found that they were passing landmarks on the surface four seconds early and reported that they were "long"; they would land miles west of their target point . </P> <P> Five minutes into the descent burn, and 6,000 feet (1,800 m) above the surface of the Moon, the LM navigation and guidance computer distracted the crew with the first of several unexpected "1202" and "1201" program alarms . Inside Mission Control Center in Houston, Texas, computer engineer Jack Garman told guidance officer Steve Bales it was safe to continue the descent, and this was relayed to the crew . The program alarms indicated "executive overflows", meaning the guidance computer could not complete all of its tasks in real time and had to postpone some of them . </P>

Who went to moon for the first time