Outside of our planet Earth, the Moon is the only other world in space that humans have set foot upon. The Moon is the Earth's closest neighbor, measuring about one quarter of a million miles away. Although close in space, the Earth and Moon are very different. The Moon is a barren place with no water, no air, no clouds and no living things. The Moon has no atmosphere. The Moon is about one fourth the size of the Earth itself, measuring at 2170 miles in diameter. Since the size of the Moon is much smaller than the Earth, its gravity is only about one sixth of the Earth's gravity. If you have ever looked at the Moon through a telescope you would notice that the surface of the Moon is uneven and rough. It is made up of hills, mountains, plains and craters. Prominently, what you see are the craters which formed more than 3 billion years ago when asteroids and meteoroids collided with the Moons surface. In looking at the Moon, you can see that there are light regions and dark regions. The darker regions on the Moon are known as the
maria
which means 'seas' in Latin. This region is smooth with few craters and low-lying plains. The maria consists mainly of basalt rock. The dark regions are what form the features of "The Man in the Moon." The lighter regions are heavily cratered highlands and composed mostly of a light colored rock known as anorthosite.
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The Moon is Earth's only natural satellite. A satellite is an object that orbits another 'parent' object. It takes the Moon about 27 days at 2,300 mph to orbit the Earth. There are many theories that tell how Earth got its satellite. Most scientists believe that that an asteroid or an object about the size of Mars, collided into Earth which then ejected massive amounts of debris from it. This is known to scientists as the 'collision ejection theory.' Simulations of this theory shows that energy as produced from such a collision can produce vaporized rock from the impact. The Moon then formed from the cooled material. Much is explained from this theory about the known properties of the Moon, its orbit and its composition. This collision would have caused ejected material to coalesce in an ecliptic plane which then caused the Moon to be put in an orbit much like its own. Another theory about how the Moon was formed states that the Moon came out of the Earth's crust. This can give evidence to its location but does not support the evidence that the Moon is made of different material including volatile gases. Still another theory explains, that the Moon may have also been 'captured' by the Earth. This theory may prove true for other planets' Moons but not for the Earth's Moon due to its shape and orbital direction.
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Phases
Just as the Earth, the Moon acquires all of its light from the Sun. Even though we can see the Moon easily at night, it does not produce any light of its own. In actuality moonlight is simply reflected sunlight. The direction of the sunlight that falls on the Moon changes which then creates images on the sunlit parts over the course of a month which is referred to as the phases of the Moon. The Moon's position in the sky changes as the Moon orbits the Earth and because of this we do not always see the whole side that is lit. When we do see an entire lit side of the Moon it is called a full Moon. When we see half of the lit side of the Moon it is called quarter Moon, while we call a silver of a lit side a crescent Moon. Each cycle of phases begins with the new Moon which is when no Moon is visible at all. We do not see a Moon at this time because the lit side of the Moon is facing entirely away from the Earth. As the Moon continues to move around the Earth in orbit, more of the lit side becomes visible to us. As viewed from Earth the waxing crescent (sliver of light) follows the new Moon and moves into first quarter (half Moon), waxing gibbous (three quarter Moon) and finally into a full Moon. Following a full Moon we see the waning gibbous (three quarter Moon), last quarter (half Moon) and the waning crescent (sliver of light) to complete the cycle.
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Waxing Crescent
(image available in print form)
The visible Moon is partly but less than one-half illuminated by direct Sunlight while the illuminated part is increasing
First Quarter
(image available in print form)
One-half of the Moon appears illuminated by direct Sunlight while the illuminated part is increasing
Waxing Gibbous
(image available in print form)
The Moon is less than fully illuminated but greater than half illuminatedby direct Sunlight while the illuminated part is increasing
Waning Gibbous
(image available in print form)
The Moon is less than fully illuminated but greater than half illuminated by direct Sunlight while the illuminated part is decreasing
Last Quarter
(image available in print form)
One-half of the Moon appears illuminated by direct Sunlight while the illuminated part is decreasing
Waning Crescent
(image available in print form)
The visible Moon is partly but less than one-half illuminated by direct Sunlight while the illuminated part is decreasing.
New Moon
(image available in print form)
The visible Moon is not fully illuminated by direct Sunlight.
Figure 1: Courtesy NASA
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Eclipses
Eclipses occur when the shadow of one celestial body falls on another celestial body. The Moon travels directly between the Earth and the Sun during a solar eclipse. During this time we see the Sun disappear and a shadow is cast from the Moon which then passes over the Earth. A lunar eclipse however, occurs when the Earth is between the Moon and the Sun. At this time, when the full Moon enters into the Earth's shadow the Moon will turn a deep red color. A lunar eclipse occurs only during a full Moon while the solar eclipse occurs only during a new Moon. Both solar and lunar eclipses follow a predictable cycle and occur approximately no more than once each year when the two paths that the Moon and Sun follow cross exactly during a new or full Moon. The eclipses of the Sun and Moon are directly tied to the lunar phase cycle.
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(image available in print form) Figure 2: Courtesy NASA
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Tides
The daily ocean tides on Earth are caused by the pull of the Moon's gravity. As the Earth rotates on its axis different parts of the world face the Moon. When the Moon passes overhead, the waters in that area are attracted to the Moon because of its gravitational pull. The Moon's gravity pulls up the water below it which causes a high tide (higher water level). At the same time, the oceans on the opposite side of the Earth also experience a high tide. Low tides occur (lower water level) on the other two sides of the Earth where water is said to be chasing after the Moon. Additionally, the Moon's gravity causes land tides. The surface of the Earth actually rises and falls as much as one to two inches when the Moon is overhead. Although the Moon's gravity can create tides by itself, it does not. The Sun also exerts tidal forces on the Earth, but these are only about half as great as the Moon's force. When the Sun, Moon and Earth become aligned at a new Moon or full Moon, the tidal effects will reinforce each other and create a large shift in the water level known as spring tides. Neap tides, on the other hand, occur during a first quarter and last quarter Moon when the Sun and Moon form a right angle with the Earth. This causes the tidal effects of the Sun and Moon to cancel each other out, creating a much smaller shift in the tides.
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An animation that shows the tidal effects of the Moon can be found at (http://science.nasa.gov/headlines/images/missingtides/dissipation.gif)
Mythology about the Moon
In myths around the world, the Moon often represents immortality or change. The Moon's ability to change forms was thought to be remarkable, and because of it many people used the Moon as guidance to know when to plant and when to reap. There are many lunar myths used to explain why the Moon waxed and waned and even why it appeared to die and resurrect. In some parts of the world, the Moon was male, such as in Australia and Mexico. Other parts of the world depicted a sibling relationship such as in Scandinavia or India. Other myths, however, made the Moon a beautiful goddess. Some placed the Moon on a chariot and married her to the Sun. All over the world, people would gaze at the Moon to see the beautiful goddess that lived there. Some even recognized her face in patterns on the surface of the Moon while still others saw images of animals. To some, spots on the Moon looked like toads, while to others they looked like rabbits. Some people thought that the patterns looked like fields of trees or even imagined that a boy, girl or the man in the Moon lived there. The various myths associated with the Moon were written by many different cultures, but all were an attempt to explain the pictures seen upon the Moon's surface. Heng O and Her Palace on the Moon is a myth from China. Heng O is the illustrious Moon goddess who brings light, life and harvest. One autumn night, Heng O swallowed a magic pill that made her immortal and float up to the Moon. Her husband, Shen I, built her a lovely palace where she lived with her rabbit. Once a month Shen I would leave Heng O and visit the palace of the Sun. It was at this time that day by day Heng O would grow sadder and sadder causing her light to grow dimmer and dimmer and by the time Shen I reached the solar palace Heng O disappeared in the darkness. This made Shen I very upset to see his wife so sad but when it was time to leave the Sun and return to Heng O, the closer he came to her, the brighter Heng O would become. When Shen I and Heng O would reunite she would dance and shine in love and happiness for all to see.
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This marriage of the Moon goddess to the Sun god appeared in other cultural myths around the world too, such as in Egypt or Greece. The marriage was a reflection of the Moon's relationship to the Sun and also explains their interdependence. The concept of yin and yang, the idea that everything in the universe has an opposite power that keeps them balanced and moving in recurrent cycles is also based on this. This myth is both representative of the yin and yang and the Moons phases as shown when Heng O becomes illuminated as her husband comes to see her each month. Because the Moon is also thought to bring good luck and happiness due to its connection to the seasons and harvest, people in China still celebrate the harvest Moon. Other cultures traditionally have a Moon goddess as well who is believed to control the cycles of the seasons and the Earth's fertility.
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The people of India pay close attention to the Moon because it is the Lunar calendar that determines the dates for their festivals. Most of them celebrate religious occasions; however they also include street parades and family events like weddings or funerals.
If you were to ask the people of India what they see in their Moon they would say a mother, Astangi Mata's handprints. Astangi Mata was known as the mother of all living things on Earth, but the sky was empty. Because she loved her twin daughters so much, she decided she would grant them everlasting life as rulers of the heavens. Suraj, was coined Raja, (i.e. the king) of the Sky. He was ever hot and the nurturer of all growing things (Sun) while Chanda was cool and ever changing, new and beautiful (Moon). As the Chanda started her journey to the sky, she missed her mother's last embrace and Astangi's hand barely brushed Chanda's cheek. To this day, that is why the Moon bears a handprint.
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The people of Scandinavia however know a different story. When they look to the sky they see a boy and a girl with a pail. Hjuki and his sister Bil worked every day and night gathering water in a pail from a magic well. One night the Moon, on seeing the children had pity on them and decided to let them come live in his house. The children were happy living there because they only had to gather water once a month. When there is a full Moon you can see the children with the pail, but over the course of a few nights, Hjuki falls out of sight. Bil later disappears, leaving the Moon dark and empty. After a few days the Moon begins to fill again and the children can be seen, first Hjuki and then Bil. This tale is one version of a familiar tale "Jack and Jill went up a hill to fetch a pail of water."
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In The Truth About The Moon, a young African boy, Sumu, is curious about the changing Moon and so his father tells him the tale that the Sun and the Moon were happily married and would shine all day together. At night however blackness would take over and no one could leave their house for fear of getting lost. So Man asked the Sun and Moon to give some light by night so that Man would not be afraid to leave their house. So the Sun and Moon decided to split up the day and night. The Sun shone all day and the Moon shone all night. Because the Sun and Moon were equally bright and equally hot however, no one could tell were the day ended and night began. Man was not happy because it was always hot and the crops were drying up. The Sun and the Moon then got in an argument because the Sun wanted to go back to the old ways were they would shine together but the Moon liked her independence and wanted to shine alone. In order to let Man sleep the Sun or the Moon had to dim his/her light. Since neither wanted to, the sly Sun ordered a swimming race across the river and the winner would get to shine in the day. As Mrs. Moon jumped in the water, Mr. Sun stopped. Mrs. Moon was made of fire and since fire and water do not mix, she lost her heat and was unable to shine as brightly. After Moon got out of the water she picked up a stick and started chasing him across the sky and to this day the Sun and Moon can not be together. They simply chase after each other night after day after night.
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Moon worship, myths and legends are an important piece of history in many cultures. There are countless tales that have been written as well as have been passed down from generations via oral tradition. Many astronomers today have lost the magic in their scientific explanations of the images seen on the surface of the Moon as well as the mystery of its waxing and waning. Although early man could not have known its scientific explanation, the Moon still symbolizes change and transformation while the Sun stands for all things permanent.
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