Know your Moon

The Moon has a prominent place in myth and folklore throughout human history.

Formation
According to a theory, the Moon was created when a rock the size of Mars slammed into Earth, short ly after the solar system began forming about 4.5 billion years ago.

Locked in orbit
Perhaps the coolest thing about the Moon is that it always shows us the same face. Since both the Earth and Moon are rotating and orbiting, how can this be? Long ago, the Earth's gravitational effects slowed the Moon's rotation about its axis. Once the rotation slowed enough to match its orbital period (the time it takes to go around Earth), the effect stabilised. Many of the moons around other planets behave similarly.

What about phases?
Here's how they work: As the Moon orbits, it spends part of its time between us and the Sun, and the lighted half faces away from us. This is called a new Moon.Once it is opposite the Sun, it becomes fully lit from our view - a full Moon.

Moon trees
More than 400 trees on Earth came from the Moon. They came from lunar orbit. In 1971, Apollo 14 astronaut Stuart Roosa took a bunch of seeds with him. Later, the seeds were germinated on Earth, planted at various sites around the US, and came to be called the Moon trees. Most of them are doing just fine.

Punching bag
The Moon's heavily cratered surface is the result of intense pummelling by space rocks between 4.1 and 3.8 billion years ago. The scars of this war, seen as craters, have not eroded much for two main reasons: The Moon is not geologically very active, so earthquakes, volcanoes and mountainbuilding don't destroy the landscape as they do on Earth; and with virtually no atmosphere there is no wind or rain.

Sister moons
The Moon is Earth's only natural satellite. Right? Maybe not. In 1999, scientists found that a 5-kilometer wide asteroid may be caught in Earth's gravitational grip, thereby becoming a satellite. Cruithne, as it is called, takes 770 years to complete a horseshoeshaped orbit around Earth, the scientists say, and it will remain in a suspended state around Earth for at least 5,000 years.

Egghead
The Moon is not round or spherical. Instead, it's shaped like an egg. If you go outside and look up, one of the small ends is pointing right at you. And the Moon's center of mass is not at the geometric center of the satellite; it's about 2 kilometers off-center.

Moonquakes
Apollo astronauts used seismometers during their visits to the Moon and discovered that the gray orb isn't atotally dead place, geologically speaking. Small moonquakes, originating several kilometers below the surface, are thought to be caused by the gravitational pull of Earth. Sometimes tiny fractures appear at the surface, and gas escapes.

Is it a planet?
Our Moon is bigger than Pluto.At roughly one-fourth the diameter of Earth, some scientists think the Moon is more like a planet. The Earth-Moon system is referred to as a 'double planet'. Pluto and its moon Charon are also called a double-planet system by some.

Ocean tug
Tides on Earth are caused mostly by the Moon . The Moon's gravity pulls on Earth's oceans. High tide aligns with the Moon as Earth spins underneath. AII this tugging has another interesting effect: Some of Earth's rotational energy is stolen by the Moon, causing our planet to slow down by about 1.5 milliseconds every century.

Bye bye Moon
As you read this, the Moon is moving away from us. Each year, the Moon steals some of Earth's rotational energy, and uses itto propel itself about 3.8 centimeters higher in its orbit. Researchers say that when it formed, the Moon was about 22,530 kilometers from Earth. It's now more than 450,000 kilometers away.