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Find your weight on the Moon!

The Moon is Earth's only natural satellite. The Moon's orbit takes it around our planet once a month (which is, of course, the origin of the word "month!"). Because it rotates at the same rate that it orbits, we only ever see one side of the Moon from the surface of Earth. The visible nearside of the Moon, with its bright highlands and dark maria ("oceans"), has been mapped in detail since Galileo turned the first telescope to the skies in 1609. Galileo's telescope revealed that the Moon wasn't a perfectly smooth sphere; as sunlight plays across the surface of the Moon, it lights up and shadows crater walls and floors. The heavily cratered lunar surface bears witness to the heavy bombardment by asteroids and comets that both Earth and the Moon have suffered over time. Unlike Earth, the Moon is now geologically quiet, its surface preserving a fossil record of its impact history.

It was not until the Space Age began that we got our first glimpse of the lunar farside, from the Soviet Luna 3 spacecraft in 1959. The Moon had hidden more surprises for all that time: the farside has virtually none of the dark maria that give the nearside its splotchy appearance, and it contains what may be the biggest and deepest impact basin in the entire solar system, the Aitken Basin.

The Moon was -- and remains -- the most popular target for any spacefaring nation's first adventurous steps into planetary exploration. It was, of course, the target of the space race between the United States and Soviet Union in the 1960s and 1970s. It is the only place in the solar system other than Earth walked upon by humans. Lately, the Moon has become a prime destination for efforts by many nations seeking to expand into space: Japan (Kaguya), China (Chang'E), India (Chandrayaan-1), and the United States (Lunar Reconnaissance Orbiter).

Moon Numbers
Size: 3,476.2 kilometers -- 0.2725 Earths -- 14th largest solar system body
Orbit: 384,400 kilometers from Earth
Calendar: 1 lunar day = 29.53 Earth days

Recent Headlines
13 Nov 07 New Image: EarthRise in HDTV

14 Sep 07 Kaguya Rockets Toward the Moon; International Lunar Decade Begins

13 Sep 07 Google Lunar X PRIZE Encourages New Space Race

19 Jan 07 "Lunar A" to Stay on Earth

20 Dec 06 Scientists Search for Distant Life in the Moonlight

05 Dec 06 Planetary Society Welcomes NASA Proposal for Lunar Outpost

18 Oct 06 New Evidence Challenges Idea of Water-Ice on the Moon

03 Sep 06 SMART-1 Mission Goes Out With a Bang

29 Aug 06 SMART-1 Prepares for Lunar Crash-Landing -- and You Might Be Able To See It

28 Jun 06 Europe and Russia Join Forces to Study Advanced Crew Transportation System