The Moon is the only other planetary body upon which humans have set foot. However, there has been a hiatus of over 30 years in the human exploration of space since that last step on the moon by an astronaut of the Apollo 17 mission. In some respects, it resembles the gap in exploration of the western ocean by Europeans following the discovery of America by the Vikings.

Times though are changing. A new space race is in progress with China, Europe, India, Japan and the United States planning missions to the moon.

Wait! With the budget deficit and economic recession, the Americans in 2010 decided that they will not be returning to the moon after all - at least not in the foreseeable future. China still plans a manned lunar mission as early as 2020.

Future manned exploration of the moon, whenever it occurs, will include the establishment of permanent bases. Initial unmanned moon exploration will be looking for local resources necessary to establish such bases, so as to minimize dependence on earth. Availability of such resources at certain sites, together with topographic advantages and ability to satisfy mission objectives, will be key in the determination of base location.

The NASA Moon page provides information focused on that planetary body. The Moon Society is an international non-profit educational and scientific foundation formed to further scientific study and development of the moon. The Lunar and Planetary Institute is a repository of information on the moon and past and future missions to the moon. The Clementine mission to the moon is an excellent source for factual information and images of the moon. The Once and Future Moon is a blog sponsored by the American Air and Space Museum.

The January/February 2007 issue of the Planetary Society's Planetary Report contains a number of articles on Why go back to the Moon? Various authors approach the question from different directions, arriving at different answers.

The Return to the Moon (RTM) Project is a long term goal of the Space Frontier Foundation to establish a large scale, economically viable, permanent human settlement on the Moon within the next 25 years. The Artemus Project is a private venture to establish a permanent, self-supporting community on the Moon. Gaia Selene is a lunar colonization advocacy site.

Lunar miner looks at lunar resources. Permanent is described by its acronym as Projects to Employ Resources of the Moon and Asteroids Near Earth in the Near Term.

Google Moon is the best place to start looking for maps of the Lunar surface. The website shows visible appearance, color coded elevation, Apollo landing sites, and charts of particular locations on the near side. Another Lunar Atlas may be found at the Lunar & Planetary Institute and the Lunar Republic.

Before 2007, the most recent mission to the moon was Smart-1 by the European Space Agency. Launched in 2004, the mission ended in September 2006 when the spacecraft impacted the lunar surface in the Lacus Excellentiae region. After a three year hiatus in moon missions, two missions were launched in 2007. These Asian missions were Kagura by Japan and Chang'e 1 by the China National Space Administration. India's Chandrayaan 1 was launched on October 22, 2008.

NASA's LRO/LCROSS mission was launched toward the moon on an Atlas V rocket in June 2009. The mission hoped to discover what the moon has to offer for the future moon dwellers. The spacecraft will be searching for safe landing sites and life sustaining elements (such as water at the poles). A final impact crater for the Lunar Crater Observation and Sensing Satellite (LCROSS) was selected in September 2009. This Quest Video portrays the impact mission, which in 2009 impacted the Moon's South Pole searching for definitive evidence of water. The impact was a success and in November 2009 NASA announced that water's presence on the moon has been confirmed. A key requirement for a permanent moon base appears to have been met.

Characteristics

The Moon is 384,403 kilometers (238,857 miles) distant from the Earth. Its diameter is 3,476 kilometers (2,160 miles). Its diameter is about half that of Mars, but larger than that of the planet Pluto. The speed necessary to escape the gravitational grip of the moon is a little over a fourth that needed from the earth. The mean temperature is -15 C compared to 20 C for earth. The moon has neither a magnetic field nor an atmosphere. Unlike the earth, the Moon's interior is no longer active.

The Moon's crust is thinner and the center of mass is offset from its geometric center on the near side toward the Earth. Both the rotation of the Moon and its revolution around Earth takes 27.32 earth days. This synchronous rotation is caused by the unsymmetrical distribution of mass in the Moon, which has allowed Earth's gravity to keep one face of the moon permanently turned toward Earth.

Given an orbital rotation equal to its period in orbit around the earth, most locations on the moon have a day of 14.75 earth days followed by a night of the same length. This total day/night cycle of 29.5 earth days is slightly greater than the Moon's orbital period of 27.32 earth days since the Earth moves a significant distance in its orbit around the Sun in that time.

Current theory indicates the Moon was formed when a Mars-sized body hit the Earth after the Earth's iron core had formed. Rocky, iron-poor material was ejected into orbit and then coalesced to form the moon. The Moon has a small core, supporting the Mars sized impact theory.

Farside

Locked in synchronous rotation, the Moon always presents its well-known near side to Earth. But from lunar orbit, Apollo astronauts also grew to know the Moon's far side. This picture from Apollo 16's mapping camera shows the eastern edge of the familiar near side (left) and the strange and heavily cratered far side of the Moon. Surprisingly, the rough and battered surface of the far side looks very different from the near side which is covered with great swaths of smooth dark lunar maria. The likely explanation is that the far side crust is thicker, making it harder for molten material from the interior to flow to the surface and form the smooth maria.

Water

Data from NASA's Clementine and Lunar Prospector space craft have made the Moon more attractive than in the Apollo days. There have been strong hints that water might exist in the permanent shadow of deep polar craters.

As a resource, lunar water could cut the cost of living dramatically for lunar explorers, since otherwise supplies would have to come all the way from Earth - at a price of anything up to 20,000 Euros per liter. It would also make a lunar 'fuel factory' a real possibility. There is plenty of oxygen bound up in the Moon's rocks, but little or no hydrogen. Even a modest water supply could guarantee an in situ source of cheap rocket propellant. With the success of the LCROSS mission, it appears water in sufficient quantity has been confirmed.