The moon is a natural satellite that orbits a planet. In our case, it is the Earth that the moon orbits. The moon is the second-largest natural satellite in the Solar System, after Jupiter’s satellite Ganymede.
The Moon was formed 4.5 billion years ago, almost immediately after the formation of the Earth. The theory of its formation is that a giant asteroid some 4 billion years ago collided with the young Earth, throwing part of its crust into orbit and solidifying it. Over time, this material underwent numerous gravitational interactions with the Earth and eventually developed into our familiar Moon.
Thanks to advanced telescopes and spacecraft missions over the past few decades, scientists have gathered a lot of data on our Moon. They have determined its mass, for example: 7.354 x 10^22 kg.
What is the significance of these numbers?
The mass of the moon is an important figure, as it dictates how the moon moves in relation to Earth. The amount of time it takes the moon to orbit Earth and its distance from Earth affect how it moves.
As mentioned before, the gravitational force between two objects is dependent on their mass. The greater the mass, the stronger the force. This is why things like paper don’t suddenly jump off your desk and hit the wall across the room, unlike a heavier object like a book would.
The moon has less mass than Earth, so its gravitational pull is weaker. Because of this, when both planets are at their closest position during each lunar cycle, the moon takes approximately two hours less to orbit Earth than it normally does.
This effect is called libration, and explains why you can sometimes see part of the far side of the moon.
How big is the moon?
The size of the moon is related to how long it takes the moon to orbit the Earth. The length of the lunar orbit is related to how fast the moon rotates on its own axis.
The moon takes 28 days to rotate on its own axis, so one side of the moon always faces the Earth. Because of this, we see half of the surface of the moon, and we call this side the lunar near side. The other half of the surface is called the lunar far side.
Because it takes 28 days for the moon to rotate on its own axis and 29 days for the earth and moon pair to complete an orbit, there is a small amount of variation in what part of the lunar surface faces us. This is what causes phases of the moon. When one side faces us, more light on that side is reflected back to us, making it appear as a new Moon.
Why does the moon have an effect on Earth?
The moon has an effect on Earth for two main reasons. The first is that the moon affects the Earth’s rotation. As the Earth spins on its axis, it must adjust for the gravitational pull of the moon, which causes the earth to slow down its rotation.
The second is that the moon affects ocean tides. As the oceans flow and surge, they are influenced by the gravitational pull of the moon. This happens twice a day, once when the moon moves from one side of the earth to the other, and again when it changes height in relation to the earth.
These effects are very small, but they add up over time. Over many years, these small changes in rotation and tidal height can have an effect on life on land.
What would happen if the moon disappeared?
While we may take the moon for granted, its disappearance would cause dramatic changes to our planet. The gravitational pull of the moon stabilizes our rotation, preventing us from wobbling too far in any one direction.
This is called rotational stability and it allows us to have day and night. Without the moon, we would rapidly spin around a single point, which would be the Earth’s center of mass.
Our days would be significantly shorter and there might even be weeks with five days instead of six. There would also be significant changes in ocean tides as well as our weather patterns.
The moon’s gravitational pull also helps to keep ocean tides steady. If this force was removed, then tidal levels could change dramatically. There could even be tidal waves higher than usual due to differences in ocean depth and how water is pushed away from shorelines by strong currents.
What would happen if the Earth moved closer to the moon?
If the Earth moved closer to the moon, lunar tides would be higher and last longer. This is because the moon’s orbit is not fixed, and its distance from Earth is not fixed.
Since both bodies move around a common centre of mass, a change in their distance would cause a change in their attraction for each other. The gravitational force between them would become stronger or weaker as a result.
The same goes for the moon: If it moved closer to the earth, its tidal height and duration would increase. Since the earth does not move, this hypothetical situation could be tested.
Could you imagine what that would do to our oceans? It would be chaotic, that’s for sure! But since this is just a thought experiment, let’s move on.
How did we find this information?
The mass of the moon was determined through gravitational measurements. We have several satellites that orbit the earth, some of which go around the moon.
Satellites are expensive pieces of technology, so we want to make sure they don’t crash into anything. For this reason, we must know the exact distance between the earth and the moon so we can adjust our satellites’ orbits to keep them at a safe distance from the moon.
We had several satellites in orbit around the earth and took measurements for a certain amount of time. By doing this, we were able to determine how fast each satellite orbited the earth. We then compared this information with how long it took each satellite to orbit the moon, which gave us the distance between them. By dividing one number by the other, we were able to find out how strong gravity is between them.
What is the significance of these numbers?
The numbers for the mass of the moon, its distance from Earth, and its orbital period are very special. They combine to form a special ratio: 1:27.3:3.8.
If any of these numbers were different, then this special ratio would not exist. For example, if the moon’s mass was even slightly greater than it is, then its orbit would be slower than it is, and the ratio of periods would be less than 1:27.3.
This is because the moon would take longer to complete an orbit, and there would be more moons per day. If the moon’s mass were smaller, then its orbit would be faster, and the ratio of periods would be greater than 1:27.3. Because there are 27.3 days between one new moon and the next, this number is part of the special ratio that exists between the mass of the moon and its period in orbit around Earth.
How big is the moon?
The size of the moon is also important to understanding lunar phases. Because the moon orbits around the Earth, we can see half of it.
Because it is an opaque object, we can see the reflected light on its surface. We know that the moon takes 28 days to complete one rotation, so a month has 28 days.
We also know that the moon takes 27 days to complete one orbit around the Earth. Because of this, there are only a few days each month when we can see the whole surface of the moon.
This is because it takes 4 weeks for one full orbit around the Earth. The details of these lunar phases are what make them tricky!
The sun plays a part in this as well. The length of time it takes for the moon to orbit the earth changes each month due to solar gravity. This adds more variation to lunar phases.
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