The Picture above is of the Astronauts on the Moon.
The Picture above is of the Astronauts on the Moon.
The Moon is the Earth's only satellite. It is the fifth largest satellite in the Solar System. It is quarter the size of the Earth. Except for Pluto and its moon Charon (which may be asteroids) no other planet in our system has such a large moon relative to its own size. The moon revolves around the earth in approximately 29.5 days, which is the same as its period of rotation. For this reason, we see only one side of the Moon. For a resident of the Moon, if living on the side facing Earth will always be able to see it. The Sun would appear to rise and set every 29.5 days.
The Moon is nearly spherical with a diameter of 3476 km. (2160 miles) The mass of the Moon is 1/81 that of the Earth and its specific gravity is 3.3 g/cm2 compared to 5.5 cm/gm3. The surface gravity is one sixth that on Earth. Thus a person on Earth weighing 150 pounds would weigh 25 pounds on Moon.
The Moon's interior is thought to be made up of a small, perhaps solid, iron rich core, a solid mantle, and a crust that is 64 km thick on the near side and 125 m thick on the far side.
Because of the dull dark surface of the Moon, its albedo is 0.07, about one-fifth that of Earth. Full Earth as viewed from the Moon appears about 14 times larger than full moon viewed from Earth and 70 times brighter. The Moon has no atmosphere. Hence except in the vicinity of the Sun, the sky would appear black.
What is the origin of the Moon?
The sister theory states that the Earth and the Moon were created at the same time. The Moon coalesced from particles revolving around Earth. This theory fails to explain the lack of iron and water on the Moon.
The great impact theory proposes that a planet sized object about the size of Mars struck Earth with a glancing blow 4.4 to 4.5 billion years ago. The impact ejected material from the Earth's mantle (where there is little iron) into orbit which formed into the Moon.
Features of the Moon:
1. Craters are the best known characteristics of the Moon. About 30,000 can be seen through a telescope, ranging in size from microscopic to hundreds of kilometers in diameter. They were caused by the impact of meteorites.
2. Multi-ring Basins. The one located at the South Pole, it is the largest known in the solar system with a diameter of 2500 Km (1550 miles), and an average depth of 12 Km (7.4 miles). There are other basins also.
3. Plains are large flat areas called Maria (an Italian word meaning "seas"). They are craters formed by the impact of hugh objects and later filled with lava.
4. Regoliths. The surface of the Moon is a terrain of rolling, rounded knolls composed of a layer of loose debris or soil called regolith, with a depth f less than 10 meters (33 feet) on the flat lunar plains.
5. Rays. Some craters are surrounded by streaks or rays, that extend outward over the surface. They are pulverized rock that was thrown out during the formation of the crater, and are brighter. The ray system of the crater has an average diameter 12 times the diameter of the crater.
6. Rills are long narrow trenches or valleys, varying in width from few meters to 5 kilometers, and extending hundreds of kilometers in length. They have very steep walls and flat bottoms. They were formed by moon quakes.
7. Mountain Ranges with peaks as high as 6100 meters (20,000 feet) which were not formed and shaped by internal forces as on Earth.
8. Faults are breaks or fractures in the surface along which vertical, horizontal, or parallel movements have occurred
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For more details of the Moon click below.
The appearance of the Moon to an observer on Earth changes, known as the phases of the moon. The new phase of the Moon (known as New Moon) occurs as the Earth, Sun and Moon are in the same plane, with the Moon being between the Earth and the Sun. The Moon cannot be seen from the Earth. The Moon revolves Eastward and for the next 7.375 days, it is seen as a waxing (getting larger) crescent (less than one quarter) Moon. At the end of this phase, we have the first Quarter. A Gibbous Moon occurs when more than one quarter is visible. After 7.375 more days, the Sun, Moon, and Earth are again in the same plane, but now the Earth is between the Sun and the Moon. Now the entire Moon can be seen and this is known as the Full Moon. The the moon starts waning (getting smaller) and 7.375 days later we have the last quarter and finally after 7.375 days (a total of 29.5 days) we are back to the New Moon.
To find the phase of the moon on any date click below
Two features of the Moon are its eclipses and the tides that they cause. For details click below.
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