One minor correction to Fraggle's excellent post.
We on the earth never get to see a true full moon because a true full moon from the perspective of the earth because when the Sun, Earth, and Moon are perfectly aligned we see a total lunar eclipse rather than a true full moon. The Apollo astronauts on the other hand could see a true full moon, and it is 30% brighter than the (nearly) full moons we get to see from the Earth.
A couple factors come into play here. The Moon's surface is quite irregular. Those irregularities create shadows that tend to be at their smallest at the point on the Moon's surface directly in line between the center of the Moon and the Sun. While this explains why a quarter Moon is much less bright than a full Moon, it doesn't explain that 30% gain in brightness that results from the 5 degree change in phase angle from the full Moon we see from the Earth and a true full Moon. The Moon's surface is covered with a lot of little glassy beads that effectively act as natural retroreflectors. The Moon is anything but a Lambert surface.
That said, the Moon is a very poor retroreflector compared to the artificial retroreflectors placed on the Moon by the Apollo astronauts.
High-quality retroreflectors do not occur naturally. Lesser quality ones do occur naturally. One place to look for natural retroreflectors: The Moon! The Moon appears to considerably brighter when it is full than it is even a day before or after full moon. This is not an optical illusion; it is very real.Retroreflectors do not occur naturally and must be built by human engineering.
We on the earth never get to see a true full moon because a true full moon from the perspective of the earth because when the Sun, Earth, and Moon are perfectly aligned we see a total lunar eclipse rather than a true full moon. The Apollo astronauts on the other hand could see a true full moon, and it is 30% brighter than the (nearly) full moons we get to see from the Earth.
A couple factors come into play here. The Moon's surface is quite irregular. Those irregularities create shadows that tend to be at their smallest at the point on the Moon's surface directly in line between the center of the Moon and the Sun. While this explains why a quarter Moon is much less bright than a full Moon, it doesn't explain that 30% gain in brightness that results from the 5 degree change in phase angle from the full Moon we see from the Earth and a true full Moon. The Moon's surface is covered with a lot of little glassy beads that effectively act as natural retroreflectors. The Moon is anything but a Lambert surface.
That said, the Moon is a very poor retroreflector compared to the artificial retroreflectors placed on the Moon by the Apollo astronauts.