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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.
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.
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.
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.
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.
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.
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.
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.
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.
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

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THE MOON

  • 1.
  • 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