No concrete evidence explains why there is a moon. The best hypothesis presented is the Giant Impactor hypothesis: It suggests that around 4.45 billion years ago, while the Earth was still forming, a large object hit the Earth at an angle.
How Stuff Works explains the Giant Impactor or Ejected Ring hypothesis: When the large object that was around the size of Mars hit the Earth, it threw debris into space from the Earth's mantle region and overlying crust. After the impact, the object of impact itself melted; and, it merged with the interior of the Earth. The hot debris merged to create the moon.
This hypothesis explains certain things, such as: why the moon has rocks that have a composition similar to the Earth's mantle, why the moon has no iron core, and, why moon rocks look as if they have been baked, although they have no volatile compounds. Computer simulations demonstrate that this hypothesis is possible.
Throughout the years there have been other theories to suggest why there is a moon. Some believe that the moon was made through fission and the Earth moved so rapidly on its axis that a large part of it during the molten stage spun off and formed the moon. Another theory is that the moon and Earth just happened to form at the same time. However, both of these theories have been proven wrong over time.Learn More
One interesting fact about the Moon lies in how it got its name. The proper name for the Moon is, simply, the "Moon." The Moon was named before humans realized other moons exist, and now "Moon" is capitalized to avoid confusion.Full Answer >
The gravitational pull of the moon ensures that the earth remains in a constant position on its axis, despite the way it is moving around the axis. Without the moon, the earth would not be able to continuously rotate and it would be uninhabitable.Full Answer >
The moon has a mass of 7.34 times 10^22 kilograms. The Earth has a mass of 5.98 times 10^24 kilograms, which makes the moon 81 times less massive than the Earth.Full Answer >
The moon appears to wax and wane through different phases due to how much of its illuminated surface is visible from Earth. At any given time, half the moon is illuminated by the sun's light. Depending on where the moon is in relation to the Earth, the amount of illuminated surface changes. The ratio of illuminated surface to shadowed surface creates the phases.Full Answer >