The Natural Satellite of The Earth

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Sometimes white, sometimes red, crescent-shaped, oval or perfectly round, the Moon has been the faithful companion of the Earth for billions of years.

Born at the same time as the Earth, the Night Lady has aged prematurely but her gaze has kept its intensity and still makes many dreamers dream who woo her when she deigns to appear above the horizon.

The Moon is not a planet because it does not revolve around the Sun; the moon revolves around the Earth. It is therefore the natural satellite of the Earth. But there are also so-called artificial satellites that revolve around the Earth and are used for telecommunications or to study our planet.

The Moon orbits very far from the Earth, at about 384000 km distance while most artificial satellites revolve around the Earth at about 500 km altitude, some at 36000 km like geostationary satellites.

The Moon is so far that it takes 4 days to reach it by rocket. We’ll talk about it in the page dedicated to the exploration of the Moon.

The Moon always has the same apparent diameter, even near the horizon where it looks much bigger. It is actually an optical illusion as seen in the photograph shown on the left: near the horizon or very high in the sky the Moon always has the same diameter!

Four times smaller and 81 times lighter than Earth, the Moon is 3476 km in diameter. It is one of the largest satellites in the solar system, as large as the Jupiter-based Europe satellite, which you can observe as a bright star in a small telescope. It represents 3/4 of the planet Mercury which is the closest planet to the Sun.

There is no atmosphere and therefore no air on the moon. This is why cosmonauts must wear a diving suit to breathe when they explore the lunar soil. The Moon lost its atmosphere shortly after its formation because its low gravity could not hold it and the gases are gradually escaped into space.

On the Moon gravity is worth one-sixth of that of Earth. A person who weighs 60 kg on Earth weighs only 10 kg on the moon! Without atmosphere the extremes of temperature are the same as in space. In the space of 8 hours, if you put an object in the shade, its temperature will fall to -173 ° C and if you leave it in full Sun it can reach about 130 ° C! But as there is no air, the heat does not spread easily and the material that remains in the sun (camera, flag, etc.) is not likely to be damaged by heat.

The lunar subsoil is so cold that it is frozen for 2 meters deep by -17 ° C. The surface resembles talc or very fine powder and is made of very compact meteorite debris that has accumulated over 10 meters thick, in which, due to the vacuum and cold it is difficult to drive a pile without the help of a hammer. On the other hand to ride in jeep off-road as have done several crews of Apollo missions, it’s great!

As there is no wind or rain on the moon, all the craters and footprints that astronauts have left behind will still be visible in millions of years. On the other hand, this phenomenon is impossible on Earth because in a few hours or a few years all traces disappear due to erosion.

But there is no liquid water on the surface or grass on the moon, only pebbles and dust. So there is no life on the moon either. The landscape looks like a silent desert full of craters and gray mountains. It must not be very funny to live up there …

View of the Earth The surface of the Moon has large dark areas called “seas” and so-called mountainous clear areas. Several hundred years ago, in Galileo’s time, it was believed that the Moon was like the Earth and that the dark areas represented large bodies of water like our oceans.

But today we know that these big dark spots are not at all seas but old giant craters that have been filled with lava by the impacts of meteorites and some active volcanoes billions of years ago. Today the Moon is almost dead and all the volcanoes are extinct. Only its core emits a little heat.

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