20 Thing you did not Know about the Moon

1.  Our Moon is the fifth largest Moon in the solar system, surpassed in size only by Jupiter’s Ganymede (the largest) and Callisto, Saturn’s Titan and Neptune’s Triton. The diameter of the Moon is 3,476 km., just 27% of the Earth’s diameter. However, relative to the size of its parent planet, the Moon takes the first place in the solar system. Its mass has a ratio of 1 to 80 to that of the Earth. If this appears insignificant, consider Triton which has the mass ratio to Neptune of 1 to 750. The solar system has no less than 169 Moons. 

1.  The Moon has an atmosphere but an extremely tenuous one, which would be considered a high vacuum by the terrestrial standards. Apollo instruments detected a collisionless gas comprised of helium, neon, argon, and radon, most of which probably come from the solar wind. If all the molecules in 1 cubic centimetre of this extremely thin Moon ‘atmosphere’ were lined up end to end, they would fit into the period of this sentence. 

1. About 5,00,000 craters on the Moon can be seen from the Earth through the largest and most powerful telescopes. It would take a person over 400 continuous hours to count them all--and these don’t even include the craters on the Moon’s far side. The largest crater, which has a diameter of 2,240 kms and an average depth of 13 kms, is also on the far side. It is the largest crater in the solar system. 

1. Tiny grains of rock and metal called micrometeorites continually strike the lunar surface. Most are from 0.01 to 0.1 millimetre in size and travel at about 1,13,000 kilometres/hour. Nevertheless, these cosmic bullets pack quite a punch possessing 100 times more energy than an equivalent mass of TNT. They created the powdery soil in which were left the first human footprints on the Moon. 

1.  Due to the Moon’s gravity, oceans rise in a high tide and then fall back in a low tide twice each day. The greatest tides occur in the Bay of Fundy which divides Canada from the United States on the eastern coast. The maximum rise in the sea level recorded here was 16.6 metres, i.e. 54 feet. If the Moon were closer to the Earth--80,000 kilometres away rather than its mean distance of about 3,84,400 kilometres--the tidal forces would be tremendously more powerful and would flood the coastal regions of the world under hundreds of metres of water. Mumbai would have to move to the higher ground of the Western Ghats. 

1. Scientists have suggested many theories to explain the origin of the Moon: That it split from the Earth about 4.6 billion years ago; that it was a separate body captured by the Earth’s gravity; that it formed in orbit around the Earth; or that it was formed from the debris thrown off when a body the size of Mars struck our planet as shown in the picture.

1. The Moon’s large size relative to our planet is responsible for the strong tidal motions not just in the Earth’s oceans, but also in its atmosphere and solid body. The lunar (plus solar) tidal effect in the center of the ocean is between 0.6 and 0.9 metre, but this height varies greatly, depending on water depth, shoreline shape, and other factors. The Earth’s atmospheric tide results in a slightly increased air pressure. When the Moon is directly overhead, it causes some tide in the Earth’s crust that raises up India, or any other land mass, about 15 cms. So everyone is walking tall at least twice a month during new and full Moon. 

1. As noted earlier, the Moon has 1/80 mass compared to that of the Earth. On the other hand, the Sun is 3,30,000 times as massive as the Earth. It would, therefore, seem that the Sun’s tidal effect on the Earth’s ocean should be greater than the Moon’s. But the Moon is about 400 times closer than the Sun, so despite its smaller mass, the Moon’s tide-raising force is 2.5 times greater.

1. The Moon makes a full orbit around the Earth in 27 days, 7 hours and 43 minutes. It also rotates on its own axis, making a complete rotation every 27 days, 7 hours and 43 minutes, so that it always presents the same side to the Earth. But since there are slight variations in the Moon’s movement, a total of 59% of its surface is visible to an observer on the Earth.

1.  Gravitational interactions between the Earth and the Moon also gradually enlarge the Moon’s orbit and slows the Earth’s rotation. The Earth rotates about its axis faster than the Moon revolves around the Earth. The Earth’s rapid rotation carries the tidal bulge of the oceans forward of the Moon’s orbit. As viewed from the Moon, the tidal bulge on the Earth is always aimed slightly ahead of the Moon’s own position. This bulge produces a small but constant gravitational force that tugs the Moon forward and lifts it into a more distant orbit around the Earth. In other words, the Moon is very slowly spiraling away from the Earth, at a rate about 3.8 cm per year. Millions of years from now, having gradually receded exceedingly far, it would take 47 days to go around the Earth instead of about 27 days today. 

1. As bright as the full Moon appears on a cloudless and clear night, the fact is that it is only reflecting about 7% of the sunlight that falls on its surface. (Enceladus, a small ice-covered Moon of Saturn, reflects about 90% of the sunlight that illuminates its surface.) The other 93% of the light that our Moon receives is absorbed by the surface and accounts for noontime temperature at the lunar equator of over 1000 Celsius, the boiling point of water. 

1.  While the crescent Moon shines, the remainder of the lunar disc can be made out in a faint, grey-blue light known as the earth shine. This is simply the sunlight reflected from Earth illuminating the Moon. The Earth shines 36 times more brightly than the full Moon. 

1. One would tend to presume that the full Moon is twice as bright as the half Moon. But this is incorrect. The fact is that a full Moon is nine times as bright as a half Moon. The reason is that the surface of the visible half Moon is extremely rough and mountainous, which makes for more shadows and less reflected sunlight. As the Moon waxes (grows) toward fullness, the sunlight falls on more smooth reflecting surface, and brightness increases proportionately. A full Moon is almost 25,000 times more brilliant than first magnitude stars.

1. Brightness of one full Moon is not equal another. This is because the distance between the Earth and the Moon varies from as little as 3,54,340 kilometres to as much as 4,04,336 kilometres. Accordingly, the light of the full Moon can vary as much as 30 percent.

1.  Only one month has ever elapsed without a full Moon. This occurred during February, 1866, the year Bombay (Mumbai) was linked to London by telegraph. The event will not repeat itself for 2.5 million years. The month would again be February. 

1. Speaking of the Moon, what do Homi Bhabha, Pythagoras, Newton, Archimedes, Faraday, Tolstoy, Gagarin, Marco Polo, Vikram Sarabhai and Aryabhatt have in common? They all are the names assigned to various lunar features.

1. No less than 24 Americans have travelled to the Moon and 12 Americans have walked on the Moon. The total duration of their lunar stay has been 12 days, 11 hours and 40 minutes. These Apollo astronauts brought back 2,200 individual samples of rock from six sites on the lunar surface for a grand total of 386 kilograms. What has largely gone unnoticed is the fact that the unmanned Soviet spacecraft Luna 16, Luna 20 and Luna 24 returned 300 grams of lunar samples from three other sites on the Moon.

1. Along with six lunar modules, US flags, scientific equipment and a plaque signed by President Richard Nixon, the Moon’s surface is peppered with thousands of footprints (see photograph below) from a dozen astronauts who landed there between 1969 and 1972. Incredibly, these apparently fragile indentations are more permanent than any manmade structure on Earth. Without wind or water to disturb them, there is no reason why, barring a freak meteoric hit, the other prints shouldn’t remain for many aeons. What will eventually wipe them away (in 10 million years or so) is the gentle downpour of micro-meteorites (cosmic particles less than 0.1 mm across) which chisel away at the Moon’s features. 

1. The last time humans walked on the Moon was December 14, 1972. They were Eugene Cernan and Harrison (Jack) Schmitt, who left a plaque with these words inscribed on it: ‘Here man completed his first exploration of the Moon, December, 1972 A.D. May the spirit of peace in which we came be reflected in the lives of all mankind.'

1. If one million tonnes of typical lunar soil were processed, they would yield about 56,000 tonnes of aluminium; 1,39,000 tonnes of iron; 56,000 tonnes of titanium; 44,000 tonnes of magnesium; 1,94,000 tonnes of silicon and 1,39,000 tonnes of oxygen. This minerals could help build a lunar colony in future.