On landing day at all three sites, it would be in the early-to-mid morning of the two-week-long lunar daylight period. At no site would the descending LM, flying in from the east, pass over mountains or large craters that could confuse its landing radar. They were very near the equator, pocked with small craters, and relatively flat, with slopes generally no steeper than 2°. The three Apollo 11 sites had much in common. The largest young crater (lower right corner) is about 100 meters wide. For a time it was also the backup landing site for Apollo 12. Known as Site 5, this was the second backup landing site for Apollo 11.
In fact, it is located in Oceanus Procellarum about 1980 kilometers west of Tranquility Base. A casual observer might mistake this 2090-meter-square swatch of the Moon for the Apollo 11 landing site on the Sea of Tranquillity. Launching on that date would have led to a landing at Site 3, within an ellipse centered at 0.42°N, 358.67☎ in Sinus Medii, near the center of the nearside hemisphere. Failure to launch on 18 July would have meant a 21 July launch and a landing at Site 5, within an ellipse centered at 1.67°N, 318.33☎ in Oceanus Procellarum. If the mission had not been able to launch on that date, its next opportunity would have occurred on 18 July. To reach Mare Tranquillitatis, Apollo 11 lifted off from Cape Kennedy, Florida, on 16 July 1969. If, however, Apollo 11's launch had been delayed - say, by a technical fault in the giant Saturn V rocket - then the landing site would have shifted west. The prime site was Site 2 in Mare Tranquillitatis. The astronauts trained to land at any of the three sites, which were designated Sites 2, 3, and 5. What is not widely known is that Apollo 11 had three target landing sites, any one of which might have become the scene of Neil Armstrong's "one small step" onto the lunar surface. Eagle touched down at 0.6742°N latitude, 23.4731☎ longitude, about 6.4 kilometers west of the planned landing point at 0.75°N, 23.62☎. The Eagle has landed." Even after half a century, those words are known to people all over the world, most of whom were not yet born when Armstrong and LM Pilot Edwin "Buzz" Aldrin became the first humans to land on the Moon. Moments later, Mission Commander Neil Armstrong declared: "Houston - Tranquility Base here. On 20 July 1969, the Apollo 11 Lunar Module (LM) Eagle touched down on a dusty, cratered plain called Mare Tranquillitatis (the Sea of Tranquility).
The green circle marks Site 2, the Apollo 11 prime site in Mare Tranquillitatis, where the Lunar Module Eagle actually landed. Yellow circles represent the final three Apollo 11 target sites. Red dots represent the five candidate Apollo 11 and Apollo 12 landing sites as of February 1968. The map above, based on an LROC global image mosaic, is a near-copy of that historic map. The map was based on photographs taken using large Earth-based telescopes. In 1969, NASA published a map showing candidate Apollo 11 and Apollo 12 landing sites.
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