The most prominent features of the Moon are its maria, Latin for "seas", because ancient astronomers believed they were actually full of water. We know now that they are basaltic lavas, ejected from volcanoes when the moon was much more geologically active. These lavas flowed into existing impact basins (except for a few exceptions) and produced the maria we see so clearly today.
Other obvious features on the Moon are its impact craters, left from billions of years of impacts unguarded by an atmosphere. Two of the largest impact craters are Daedalus and Copernicus. Many of the Moon's craters derive from a period called the Late Heavy Bombardment, which occurred approximately four billion years ago, when much of the stray asteroids in the solar system were still aggregating into larger bodies and finding stable orbits.
The Moon is also conspicuous in its largeness. Aside from being the most obvious thing in the night sky, the Moon (also known as Luna) is the fifth largest natural satellite in the solar system, after Ganymede, Titan, Io, and Callisto, moons of Jupiter and Saturn. The Moon is large enough to maintain a level of gravity approximately one-sixth that of Earth, low enough to allow astronauts to jump about six times higher there than they are able to on the home planet.
The Moon is also set apart from other celestial bodies in being the only extraterrestrial body that has been visited by human beings, and several occasions. Now, America and China are both working on a space program to visit the Moon once again. Because of its proximity to Earth and abundance of oxygen (in rock form), the Moon is frequently cited as a possible extraterrestrial colonization target. NASA has recently solicited artists' impressions of colonists living and working on the Moon.
The appearance of the Moon that we're familiar with is so old and ingrained, it seems hard to imagine how it might look with lighted human colonies, illuminating the surface of the Moon with little dots, just as the Earth looks from space. Yet, it's only a matter of time!
Michael is a longtime WiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.