NASA's Apollo missions to the Moon took place during the 1960s and 1970s, and the astronauts did not rely on the visibility of stars to navigate or land on the Moon. The primary method of navigation used during the lunar missions was through a combination of visual references, precise tracking from Earth-based radar systems, and onboard guidance systems.
The Apollo spacecraft used a navigation system known as the Apollo Guidance Computer (AGC). This computer, along with other navigation instruments, provided the astronauts with accurate information about the spacecraft's position, velocity, and orientation in space. They could use this data to make course corrections and ensure they were on the correct trajectory to reach the Moon.
During the descent to the lunar surface, the astronauts relied on the Lunar Module's radar system. This radar provided altitude and velocity information, allowing the astronauts to control their descent and land safely on the Moon. They also had visual references, such as landmarks and craters on the lunar surface, which helped them gauge their position and altitude.
As for the lack of visible stars during the daytime on the Moon, the astronauts didn't need them for navigation. The Moon's surface reflects sunlight, creating a bright environment similar to daylight. In such lighting conditions, the stars are not visible due to the overpowering brightness of the Sun and the scattered sunlight in the lunar atmosphere.
In summary, NASA's Apollo missions used a combination of onboard guidance systems, radar data, visual references on the lunar surface, and precise tracking from Earth to navigate and land on the Moon. The visibility of stars during the daytime was not a factor in their navigation methods.