The Moon is not a planet. It orbits the Earth and is our only natural satellite. But it is a special object and has a few amazing facts attached to it. And that is why it deserves its own blog article.
The Moon is big. It’s not the biggest satellite in the solar system although it does weigh in at number five. But it is the biggest when compared to the planet it orbits. In fact the Moon is approximately one quarter the diameter of the Earth.
And it does look spectacular in the night sky. Next to the Sun, it is the brightest object we can see. However, the Moon does not radiate any light itself. Instead, like the planets in the solar system, it reflects the sunlight striking it. The light we observe is a whitish colour. But this is not the true colour of the Moon. It is in fact dark grey. It’s just that the bright sunlight against the blackness of space makes it appear white to our eyes.
We believe the Moon was created about 4.5 billion years ago as the solar system was forming. And it wasn’t a quiet birth. The Earth was still in its infancy, when along came a wandering object about the size of Mars. It collided with the Earth and during the massive destructive forces which were unleashed, a huge amount of debris was thrown up. The cloud of rock and particles was captured by the Earth’s gravity and over a very long period of time, they came together and formed a larger and larger body of matter. Eventually this body became our Moon.
It may look amazing in the night sky but the Moon is a lifeless world. With a pair of binoculars you can easily see the thousands of craters that pockmark the surface. These are due to meteor impacts over millions of years. The thick atmosphere around the Earth is able to burn up the vast majority of meteors that try to hit us. We see these incursions as “shooting stars” and most are destroyed long before they can reach the surface. But the Moon has no atmosphere and so there is nothing to protect it from impacts.
Further examination reveals that the surface of the Moon has vast flat areas which were wrongly termed “seas”. They are in fact ancient lava plains from a time when the Moon was volcanically active. The first Moon landing by the astronauts in Apollo 11 was within the Sea of Tranquillity. Neil Armstrong when he stepped on the surface for the first time described it as being covered “by a fine dust.”
By astronomical standards the Moon is very close to us. On average, it is about 239,000 miles away. It is thought to have a small metallic core surrounded by a thick rocky mantle. Just below the fine dusty surface is a granite-like crust. Because there is no atmosphere and low gravity at one sixth that of the Earth’s, it has been reported that the footprints made by the astronauts will last forever. But this is not true. Micrometeorites continue to bombard the Moon’s surface and these will eventually obliterate the marks made. However, it will take a very long time for this to happen.
I said earlier that there were a number of amazing facts about the Moon which makes it quite unusual. For example, we only ever see one side of the Moon. This is because the Moon’s orbit around the Earth matches the Earth’s rotation in such a way that only one side is ever shown to us.
The other side is called the dark side. This isn’t a very good description either, because at every new moon phase when the disc of the Moon facing us is dark, the other side away from us is lit by the Sun. These different phases of the Moon when we see it as either full, crescent or unlit are caused by the Moon’s relative position to the Sun.
Because the Moon is relatively large for a body so close to us, it is also the major reason why we have tides. It is true that the Sun also has an effect on the tides but this is quite small when compared to the Moon’s influence. On the side of the Earth which is facing the Moon at any one time, the oceans “bulge out” causing high tides. However, the Earth and Moon interact in a particular way and as a result there is also a “smaller” high tide at the same time but experienced on the other side of the Earth.
A coincidental fact is that the Moon looks exactly the same size in the sky as the Sun. The mathematics behind this is quite simple. The Sun is 400 times larger than the Moon but it is also 400 times further away. Therefore we see both of them as the same size in the sky. Although this just happened by coincidence, it does mean that every so often a part of the world is subjected to a total solar eclipse. And that is a truly amazing thing to witness.
It occurs when the Moon comes between the Earth and the Sun and exactly covers the disc of the Sun. The light from the Sun is blocked out and day turns to night. The effect can last a couple of minutes at each location. But the phenomenon of a total solar eclipse is quite a rare event. Astronomers get very excited when a total solar eclipse is going to take place and will happily travel to anywhere in the world to witness it. This is because it allows them to study the atmosphere of the Sun which is very difficult to observe at any other time.
If total solar eclipses are rare, then there is a more common phenomenon called a lunar eclipse. This occurs when the Earth passes between the Sun and the Moon. As it does, the Earth casts a shadow which dims the Moon. However, because some of the sunlight is able to “bend” around the Earth, the Moon is never blotted out entirely. But it does go a deep red colour which is worth observing.
So what does the future hold for the Moon? It was last visited in the 1970s. We haven’t been back since but there are plans to return humans there in 2024. We believe there may be valuable mineral deposits and possible sources of power held within the lunar rocks. In addition, the low gravity may make it a viable choice to launch future space craft which is another area of research by NASA and some of the commercial space companies. The Moon may be a dead world, but it is likely to soon be home to visiting astronauts.
John Pullen 