The moon is the second brightest object in the sky after the sun. The moon orbits around the Earth once per month. The angle between Earth, the moon, and the sun changes. This is the cycle of the moon's phases.

      The moon is the only extraterrestrial body humans have visited. In 1959, The Soviet spacecraft became the first to visit the moon. The first landing was on July 20, 1969.  American astronaut, Neil Armstrong, became the first human being to set foot on the moon.

    The moon is also the only body from which samples have been brought back to Earth. In 1994, the moon was extensively mapped by the space craft Clemintine. It was mapped again in 1999 by Lunar Prospector.

      The moon has no atmosphere. Evidence from Clemintine shows that there is water ice in some deep craters near the moon's south pole. The moon's South Pole is in permanent shade.

     There are two types of terrain of the moon. The terrain includes the heavily cratered and very old highlands and the smooth and younger Maria. The Maria makes up about 16% of the moon's surface and has huge impact craters that were later flooded by molten lava. Most of the moon's surface is covered with regolith. It is a mixture of fine dust and rocky debris produced by the meteor impacts.

    The moon presently has no global magnetic field. Some of the surface rocks have remnants of magnetism.  This indicates there might once have been a global magnetic field in the moon's history.        

    Because of having no atmosphere and no magnetic field, the moon's surface has been directly exposed to solar wind. Over the moon's lifetime many hydrogen ions from the solar wind have become embedded in the moon's regolith. The samples of regolith that have been brought to Earth have proved to be valuable in studies of the solar wind. Lunar hydrogen may perhaps one day be used as rocket fuel.