The Earth’s Moon is the second brightest object in the sky,
after the Sun, as seen from Earth because of its closeness,
at an average distance of 384,000km (239,000 miles) Its diameter
is 3476 km (2160 miles).

The Earth and the Moon orbit around a common centre of gravity; as the Moon goes around the Earth it is seen to go through a sequence of phases as the portion
of the illuminated hemisphere visible from Earth changes. Observers on Earth always see the same side of the Moon because its orbital period around the planet is the same as its axial rotation period.

The features on the surface of the Moon can be divided into the darker maria (seas), which are low-lying volcanic plains, and the brighter highland regions, or terrae (land), which are found mainly in the Moon’s southern left and right side as viewed from Earth.

The origin of the Moon is not known; current theories suggest that a Mars-sized object may have collided with the newly formed Earth and the Moon is the result of the debris forming into a satellite.

The Moon has a tenuous atmosphere and its rocks are igneous; surface temperature variation is extreme, from 100 to 400 kelvin.

In 1998 Earth scientists confirmed that water is present in ice near the poles.