The Moon is Earth's natural satellite and orbits our planet in synchronous rotation. It formed over 4 billion years ago when a Mars-sized object collided with Earth, ejecting debris that coalesced into the Moon. The leading theory is the giant impact hypothesis. The Moon has no atmosphere and its landscape and composition differ from Earth's due to the lack of weathering and tectonic activity. Its gravitational pull causes Earth's ocean tides to rise and fall in regular cycles.

2. The Moon
The Moon is Earth's only natural satellite. Although not the largest natural satellite
in the Solar System, it is, among the satellites of major planets, the largest relative to
the size of the object it orbits. It is the second-densest satellite among those whose
densities are known (after Jupiter's satellite Io).
The Moon is in synchronous rotation with Earth, always showing the same face with
its near side marked by dark volcanic marteria that fill between the bright ancient
crustal highlands and the prominent impact craters. It is the second-brightest
regularly visible celestial object in Earth's sky (after the Sun), as measured by
illuminance on the surface of Earth. Although it can appear a very bright white, its
surface is actually dark, with a reflectance just slightly higher than that of worn
asphalt. Its prominence in the sky and its regular cycle of phases have, since ancient
times, made the Moon an important cultural influence on language, calendars, art,
and mythology. The Moon's current orbital distance is about thirty times the
diameter of Earth, causing it to have an apparent size in the sky almost the same as
that of the Sun. The Moon's linear distance from Earth is currently increasing at a
rate of 4 cm per year, but this rate is not constant.

3. Composition
The geology of the Moon (sometimes called selenology, although the
latter term can refer more generally to "lunar science") is quite different
from that of Earth. The Moon lacks a significant atmosphere, which
eliminates erosion due to weather; it does not possess any form of plate
tectonics, it has a lower gravity, and because of its small size, it cools
more rapidly. The complex geomorphology of the lunar surface has been
formed by a combination of processes, especially impact cratering and
volcanism. The Moon is a differentiated body, possessing a crust, mantle
and core.

4. The creation of the Moon
After the sun spun to light, the planets of the solar
system began to form. But it took another hundred
million years for Earth's moon to spring into
existence. There are three theories as to how our
planet's satellite could have been created: the
giant impact hypothesis, the co-formation theory
and the capture theory.

5. Giant impact hypothesis
This is the prevailing theory supported by the scientific community. Like
the other planets, the Earth formed from the leftover cloud of dust and
gas orbiting the young sun. The early solar system was a violent place,
and a number of bodies were created that never made it to full planetary
status. According to the giant impact hypothesis, one of these crashed
into Earth not long after the young planet was created.
Known as Theia, the Mars-size body collided with Earth, throwing vaporized chunks of the young
planet's crust into space. Gravity bound the ejected particles together, creating a moon . This sort
of formation would explain why the moon is made up predominantly of lighter elements, making it
less dense than Earth — the material that formed it came from the crust, while leaving the planet's
rocky core untouched.

6. Co-formation theory
Moons can also form at the same time as their parent planet. Under such an
explanation, gravity would have caused material in the early solar system to
draw together at the same time as gravity bound particles together to form
Earth. Such a moon would have a very similar composition to the planet, and
would explain the moon's present location. However, although Earth and the
moon share much of the same material, the moon is much less dense than our
planet, which would likely not be the case if both started with the same heavy
elements at their core.

7. Capture theory
Perhaps Earth's gravity snagged a passing body, as happened with other moons
in the solar system, such as the Martian moons of Phobos and Deimos. Under
the capture theory, a rocky body formed elsewhere in the solar system could
have been drawn into orbit around the Earth. The capture theory would explain
the differences in the composition of the Earth and its moon. However, such
orbiters are often oddly shaped, rather than being spherical bodies like the
moon. Their paths don't tend to line up with the ecliptic of their parent planet,
also unlike the moon.
Although the co-formation theory and the capture theory both explain some
elements of the existence of the moon, they leave many questions unanswered.
At present, the giant impact hypothesis seems to cover many of these
questions, making it the best model to fit the scientific evidence for how the
moon was created.

8. Tides
The word "tides" is a generic term used to define the
alternating rise and fall in sea level with respect to the land,
produced by the gravitational attraction of the moon and the
sun. To a much smaller extent, tides also occur in large lakes,
the atmosphere, and within the solid crust of the earth, acted
upon by these same gravitational forces of the moon and sun.
What are Lunar Tides?
Tides are created because the Earth and the moon are
attracted to each other. The moon tries to pull at anything on
the Earth to bring it closer. But, the Earth is able to hold onto
everything except the water. Since the water is always
moving, the Earth cannot hold onto it, and the moon is able to
pull at it. Each day, there are two high tides and two low tides.
The ocean is constantly moving from high tide to low tide, and
then back to high tide. There is about 12 hours and 25
minutes between the two high tides.

9. The different types of Tides
Spring Tides
Spring tides are especially strong tides (they do not have anything to do with the season Spring).
They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the
Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new
moon.
Neap Tides
Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the
Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter
moons.
The Proxigean Spring Tide is a rare, unusually high tide. This very high tide occurs when the
moon is both unusually close to the Earth (at its closest perigee, called the proxigee) and in the
New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide
occurs at most once every 1.5 years.

10. Lunar Phases
The phases of the moon are caused by the relative positions of the earth, sun, and moon. The moon
goes around the earth in 27.3 days, or 27 days 7 hours 43 minutes, on average. This measurement is
relative to the stars and is called the sidereal period or orbital period. However, because of the
earth's motion around the sun, a complete moon cycle (New Moon to New Moon) appears to
earthbound observers to take a couple of days longer: 29.5305882 days to be exact. This number is
called the synodic period or "lunation", and is relative to the sun.
The sun always illuminates the half of the moon facing the sun (except during lunar eclipses, when
the moon passes through the earth's shadow). When the sun and moon are on opposite sides of the
earth, the moon appears "full" to us, a bright, round disk. When the moon is between the earth and
the sun, it appears dark, a "new" moon. In between, the moon's illuminated surface appears to grow
(wax) to full, then decreases (wanes) to the next new moon. The edge of the shadow (the terminator)
is always curved, being an oblique view of a circle, giving the moon its familiar crescent shape.

11. CURIOSITIES
China's mission to
robotically land on
the moon next
month is sure to
stir up lunar dust,
but it may also
cause a political
dustup, too.
Amateur photographer Kevin
Hsu was just finishing up a
shift as resident radiologist at
Medical Center in the Bronx,
N.Y. when he learned NASA's
Lunar Atmosphere and Dust
Environment Explorer
(LADEE) moon probe would
be soaring across the night
sky over New York City in
roughly twenty minutes — just
enough time to grab a camera
to capture the show.
Engineers have
fixed a technical
glitch on NASA's
newest robotic
moon explorer,
bringing the
spacecraft back
up to full health
one day after a
spectacular
nighttime launch
Friday that wowed
spectators up and
down the U.S.
East Coast