Changes

===Rotation and revolution===

===Rotation and revolution===

The Moon presents the same side to [[Earth]] at all times.  That means that the rotation of the Earth offsets the separate effects of lunar revolution. Physical explanations rely on [[tidal locking]], asserting that tidal forces on Earth caused a bulge on the Moon, thereby creating a drag on the rotation of the Moon until the same side always faced the Earth.<ref>The same theory suggested that the planet [[Mercury]] had a similar locked rotation due to gravitational forces from the sun, such that the same side of Mercury always faces the sun. In fact, that is false.  [[Mercury]]'s tidal locking is incomplete and it does not always present the same face to the sun.</ref>  In fact, current tidal forces exerted by the [[Earth]] on the Moon cannot account fully for its bulge or egg shape.<ref>"[http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT308/HTML/AT30803.HTM Chapter 8, Section 3: The Rotation of the Moon]," "Astronomy Today", Department of Physics, Fort Lewis College, Durango, [[Colorado|CO]]. Accessed February 18, 2008</ref>

The Moon presents the same side to Earth at all times.  That means that the rotation of the Earth offsets the separate effects of lunar revolution. Physical explanations rely on [[tidal locking]], asserting that tidal forces on Earth caused a bulge on the Moon, thereby creating a drag on the rotation of the Moon until the same side always faced the Earth.<ref>The same theory suggested that the planet [[Mercury]] had a similar locked rotation due to gravitational forces from the sun, such that the same side of Mercury always faces the sun. In fact, that is false.  [[Mercury]]'s tidal locking is incomplete and it does not always present the same face to the sun.</ref>  In fact, current tidal forces exerted by the Earth on the Moon cannot account fully for its bulge or egg shape.<ref>"[http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT308/HTML/AT30803.HTM Chapter 8, Section 3: The Rotation of the Moon]," "Astronomy Today", Department of Physics, Fort Lewis College, Durango, [[Colorado|CO]]. Accessed February 18, 2008</ref>

===Lunar origin theories===

===Lunar origin theories===

== Other moons ==

== Other moons ==

[[Image:Many_Moons.jpg|250px|left]]

[[Image:Many_Moons.jpg|250px|left]]

While the Moon of [[Earth]] is the best-known satellite of any [[planet]], other planets in our solar system also have moons. Earth has the least number of moons (one), while [[Jupiter]] has sixty-two. The first extraterrestrial moons to be discovered were the four Galilean moons ([[Io]], [[Europa (moon)|Europa]], [[Ganymede]], and [[Callisto]]. Next to these, Earth's Moon is one of the largest, but Jupiter and [[Saturn]] have moons in orbit about them that might qualify as planets if they orbited the [[Sun]] instead.

While the Moon of Earth is the best-known satellite of any [[planet]], other planets in our solar system also have moons. Earth has the least number of moons (one), while [[Jupiter]] has sixty-two. The first extraterrestrial moons to be discovered were the four Galilean moons ([[Io]], [[Europa (moon)|Europa]], [[Ganymede]], and [[Callisto]]). Next to these, Earth's Moon is one of the largest, but Jupiter and [[Saturn]] have moons in orbit about them that might qualify as planets if they orbited the [[Sun]] instead.

=== Sizes of moons ===

=== Sizes of moons ===