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Astronomy: Moon

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The Moon has an official name of Luna and is an astronomical object situated close to Earth, making it the only natural Earth’s satellite and the first one to be visited by humans (the Apollo ?? astronauts). The Moon formed around 4.6 billion years ago, has a diameter of 3,476 km with a distance of 384,400 km from Earth (, 2012). The Moon rotates around Earth, which takes it about 27.322 days. It has a mass of 1.23% that of the planet Earth. Its core is mainly rich in iron, and its surface is composed majorly of rocks. The temperature on its surface is 2250F (1070C) during the day, which drops to – 2430F (-1530C) during the night. The surface is also heavily cratered in a result of the bombardment of asteroids when the solar system was evolving. The surface is also flooded with basalt lava from the volcanic activities of the evolution time. Solidified lava formed level plains, which today are known as seas. The seas, however, lack water, and there is neither an atmosphere on the Moon (Bennett, 2005). The gravitational pull on the Moon’s surface is only 1/6 as strong as that on the surface of Earth, making it quite weak to maintain any gases. However, a light and temporary blanket atmosphere of sodium and potassium is available.

The tidal forces found between the Moon and Earth are responsible for the slow rotation of the satellite, leading to it being locked with its orbit all-round Earth. The same side of the Moon always faces Earth while the half facing the sun is illuminated (, 2012). It is obvious that the amount of the surface of the lighted Moon that humans can see often changes, leaving some part shaded by Earth. The lunar tides also act to slow down the rotation of Earth and increase the lunar orbit. Tidal forces often constitute a stretching force in the direction of the attracting object and also a compression force at right angles to the same attracting object. The Moon, therefore, is always stretched by about 20km along its axis. The lunar effect on Earth is often small because our planet is rather massive compared to the Moon (Cornell University, 2011). During the times when the Moon is directly underfoot or overhead, the land surface is pulled one foot higher courtesy of the moon’s tidal force; resulting into two high tides daily. Oceans become mobile, giving them an experience of about six feet high tides. Apart from the lunar tides, the Earth surface is also subjected to solar tides of the same magnitude.

The Moon can rotate on its own axis just like Earth, which often takes about 29.5 days. It is also able to revolve around its elliptical orbit, thus around Earth. During the revolution, the Moon may appear to be close (perigee) or farther (apogee) from Earth. During perigee, the Moon appears large while during apogee, it appears small. The new Moon is seen when Earth, Moon, and the Sun are roughly aligned, and they are invisible from Earth (Bennett, 2005). The first quarter is observed when half of the visible side of the Moon is illuminated and is seen almost a week after the new Moon. Waxing period represents the time between the new Moon and the full Moon. In between the quarter Moon and the full Moon, the shape changes to somewhat rounded on both sides, during which, it is called the gibbous Moon (, 2012). The last quarter Moon is seen after a week from the appearance of the full Moon, and this period of changing from the full Moon to the new moon is known as waning period.

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