My Science School

 

          The Moon has a dark side. Don’t worry; we are not talking about anything evil here. The side that faces away from the Earth is known as the Moon’s dark side. This is because of the shape of the lunar orbit.

          We know that the lunar orbit is elliptical. As a result, the Moon travels at different speeds at different points. Because of this, we can see more than half of the Moon’s surface. This phenomenon is known as libration. About 59 per cent of the Moon’s surface is visible from the Earth because of this phenomenon. Johannes Hevelius studied librations in detail and published his findings in 1647. His work was titled Selenographia.'

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          Many planets in the solar system have natural satellites. But Earth and its natural satellite share a special relationship.

          The Moon is Earth’s only natural satellite. Though our Moon is small when compared to the moons of Jupiter or Saturn, its size in relation to that of Earth is quite large.

          Along with revolving around the Earth, the Moon also revolves around the Sun in sync with the Earth. They look more like two sister planets than a planet and its satellite.

          Therefore, together, the Earth and the Moon are considered as a double planetary system.

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          The Moon has a near side and a far side. The side that permanently faces the Earth is known as the near side while the side that faces away is known as the far side. Though these sides are so, the amount of sunlight they receive is almost the same.

          The surface of the near side differs from the far side; the near side is covered by large patches of dark areas. Early scientists proposed that these dark areas were seas with water. The dark patches are still known as seas. The far side does not have such seas. The crust here is thicker than the side facing the Earth.

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          The Earth takes 24 hours to complete one rotation. But the Moon’s rotation is not that short; it takes 27 days, 7 hours and 43 minutes for the Moon to complete one rotation.

          The Moon’s axis is similar to that of the Earth; it is tilted towards one side. The Moon completes one round in its orbit around the Earth in almost the same time taken for one spin.

          Since the time taken for both movements are the same, the Moon always keeps the same side facing the Earth. This means that we get to see only one side of the Moon.

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          The Moon’s orbit is elliptical; it is shaped like a flattened circle. Because of this shape, the distance between the Moon and the Earth is different at different positions and it varies as it moves around the Earth.

          When the Moon is closest to the Earth on its orbit, it is said to be at perigee. The word perigee is of Greek origin and means ‘near Earth’. At perigee, the Moon is 356,400 kilometres away from the Earth.

          The word apogee comes from a Greek word that means ‘far from Earth’. When the Moon is at the farthest point from Earth in its orbit, it is said to be at apogee. At apogee, the Moon is 406,700 kilometres away from the Earth.

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          The Moon is the biggest and brightest object that one can spot on the night sky. It appears quite large because it is the closest celestial body to Earth.

          The equatorial radius of the Moon is around 1737 kilometres and the equatorial diameter is about 3472 kilometres. It is almost one-fourth the size of Earth. You can roughly fit in four moons inside the Earth. The Moon’s surface is as big as North and South America put together. According to NASA, “if Earth was the size of a nickel, the Moon would be about as big as a coffee bean.”

          The Moon is not a perfect sphere, just like the Earth. It is slightly flattened towards the poles. The diameter of the Moon from pole to pole is lesser than its equatorial diameter.

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          Poets often describe the silvery moon. But, the Moon doesn’t always appear silvery; it is sometimes white, sometimes yellow, grey or even red at times.

          When the Moon is low in the sky, it is closer to the horizon. The light that travels through the air scatters near the horizon as it passes through a thick layer of atmosphere. As a result, the Moon looks yellowish or orange at times. When the Moon is high in the sky, the scattering effect is much lesser and it appears whitish. During a total lunar eclipse, the Moon appears to be red; this too is caused by the scattering of light. The colours of the Moon give us clues about the minerals present on its surface.

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          Even if there are a thousand stars in the sky, it will look a bit dull if we can’t spot the Moon. It is the brightest object in the night sky. But, the Moon does not have a light of its own. How ironic!

          Moonlight is produced when sunlight is reflected by the white dust on the Moon’s surface. The Moon will reflect only 3-12 per cent of the sunlight that hits its surface.

          The other factors that influence the brightness of the Moon include the movement of the Moon around the Earth and the simultaneous movement of the Earth around the Sun.

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          Some of you might have dressed up as astronauts for your school fancy dress competition. Was it easy for you to walk around in the costume? Surely not.

          An astronaut has to carry equipment with necessary supplies like oxygen. Their space suits are usually very heavy, weighing more than 90 kilograms. But, they walk around quite easily. This is because of the Moon’s lower gravitational pull.

          The Moon’s mass is 81 times smaller than the mass of the Earth. As a result, the force of gravity on the Moon is six times weaker than that on the surface of the Earth. A bag that would weigh six kilograms on Earth would weigh just one kilogram on the Moon. Astronauts feel lighter because of this reason and walk easily on the surface of the Moon.

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          Neil Armstrong set foot on the Moon in 1969. If one were to visit the Moon now, one could still find the footprints that he left behind in 1969.

          If you leave a footprint on sand or mud on Earth, either wind or rain would wash it away and it would soon disappear. On the other hand, the footprints left on the Moon last almost forever. Wonder why? Unlike on Earth, there is no wind or water on the Moon to wash it off.

          Therefore, the footprints won’t be eroded and will last for a really long time. So don’t expect to do something mischievous on the Moon and get away with it as your footprints will give you away!

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          We know that meteors fall like missiles on the surface of the Moon as there is no atmosphere to protect it. Instead of water, comets and chunks of asteroids rain on the surface of the Moon and their impact creates craters. These are known as impact craters.

          Craters are formed due to powerful volcanic explosions as well. When the Moon’s surface is pushed upwards by melted rock, hot lava and gases gush out of it, giving rise to craters. Some craters are more than two billion years old. Generally, the age of a large crater is determined by counting the number of smaller craters it contains.

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          The Moon’s surface is covered with flat, circular sunken areas known as craters. Some craters like Clavius are so big that they can be seen even without the help of a telescope. Clavius is 235 kilometres wide and is surrounded by huge mountains. Some craters however, are very small in diameter.

          The arrangement of mountains around a large crater is peculiar; they form a circular wall. These mountains slope down gently towards the outer surface while they form a steep slope inside. When Galileo first observed craters, they looked like cups. He named craters so from the Latin word for cup.

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          We know that the Moon does not have a protective layer of atmosphere around it. Likewise, there is no wind, rain or clouds on the Moon. There is only vacuum, and sound cannot travel through vacuum. Therefore, unaided communication is not possible on the Moon. This problem can be solved with the help of a radio.

          The helmets that astronauts wear are equipped with a device that would convert the sound waves to radio waves. Radio waves are electromagnetic in nature and can travel through vacuum. These radio waves are in turn transmitted to the ground or to their fellow astronauts.

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