Moon

The Moon is the only natural satellite of Earth. It is in synchronized rotation with our planet, meaning that it always faces Earth with the same side, no matter from where it is viewed.

Seen from Earth, it is the brightest object in the sky, right after the Sun. When viewed from the ground, the Moon, coincidentally, is about the same size as the Sun, allowing for total Solar eclipses.

The Moon moves away from Earth, about 3,8 cm per year. In 500 million years, a total Solar eclipse will therefore no longer be possible.

The formation of the Moon is believed to be caused by a collision of Earth with a Mars-sized planet, known as Theia. This happened not long after the Earth itself was formed, thus not effecting life on the planet.

Effects on the Earth are tidal, meaning that it pulls Earth's oceans towards it, creating high tide and low tide. Another effect the moon has on Earth is that it slows the rotation, by about 2 milliseconds per century.