The earth’s moon is the fifth largest moon in the solar system and 4.51 billion years old. It shows it’s face at night and reminds us that it’s time to sleep, but is there more to this large rock in the sky?
The moon is so called because we didn’t know that there were others out there until Galileo Galilei discovered 4 around Jupiter in 1610. It is the only natural satellite of earth, and plays a large part in the moderation of our planet. The moon is less than a third of the width of the earth, and is thought to have been created when a Mars sized planet collided with earth, but this is not known for sure. The moon is currently 238,855 miles away from earth and moves an inch further away every year. What are the consequences of having our moon?
Tides are probably the first thing to come to mind. We all know the moon controls tides, but do you really know why? The gravitational effect imposed by the moon’s presence is greater on the side of the earth facing it, moderate to the centre of the earth, and weak for the opposite side facing it. As a result, water on the planet is pulled to one side of the earth or the other, dependant on which side is facing the moon. Due to the rate at which the earth rotates, we get high tides twice a day and low tides roughly 6 hours later. As we rotate, the position of the moon changes relatively and the gravitational pull it causes moves the oceans accordingly. This is the tidal effect. The largest recorded difference between high and low tides (i.e. tidal range) is 16.3 metres and is seen at the Bay of Fundy, on the east coast of Canada. If the moon was no longer in the sky, tidal range would not be very large. The sun also has a tidal effect meaning some tides would still occur, but the sun is a lot further away than the moon and thus the sun’s pull is felt less, and tides would not change as much.
The gravitational pull of the moon which effects the tides, also effects the length of days. The moon’s pull acts as a brake, it causes tidal friction. By pulling the earth’s water, the moon slows the spin of the earth. Over 100,000 years, tidal friction slows the earth’s spin by an average of 2 seconds. This may not sound very impressive but the moon is 4.51 billion years old, meaning that when the moon was first created, a day on earth was much shorter than it is now! By slowing the earth’s spin, the moon has actually lengthened days to the 24 hours we now know because of the gravitational pull on our oceans. That’s impressive. Professor Sasaki, from Kyoto University, summarised the changing length of a day well through this LINK. Billions of years ago, a day on earth was only 4 hours long. Over time, and as the moon moved further from the planet, the length of a day increased to the 24 hours we now have. Not great for those of us who would prefer shorter working days. Let’s see how long it is before someone protests to get rid of the moon when they find this out…
Another perk of the moon is that it stops us from wobbling as much. The earth naturally wobbles on its axis slightly, much like a spinning top. The pull of the moon prevents the wobble from being more violent, keeping us more stable. More importantly than this, the stabilising effect prevents a more extreme climate. Without the gravitational pull of the moon, the earth’s axis tilt would vary a lot more. Currently the average angle tilt of the earth is 23.5 degrees, with a range between 22.1 and 24.5 over the last 41,000 years. If the moon was not present, and there was no gravitational force pulling at the earth, this angle could change dramatically. There would be nothing stopping the earth from tilting completely on its side (i.e. 90 degrees) or from being completely straight (i.e. 0 degrees). In the first instance, at a 90 degree tilt, the seasons would be completely different, with extreme differences in temperature and weather throughout the year. If the earth had no tilt (i.e. 0 degrees), day and night would be the same length all year and we would have no seasons. There would be nothing preventing the earth from moving between these positions. Such a system can been seen on Mars, where there is no moon. When there is a large tilt, the ice caps on Mars can reach from the poles to the planet’s equator.
Overall, the moon plays a few vital roles controlling tides, making days the perfect length (for some), and aiding the ideal (it may not always feel like it) climate that we have throughout the year. Next time you see that big rock in the sky at night, think of all the things you have because of it. This great NASA website provides an interactive look at the moon and plenty more facts and figures to play with.