situations

The Moon is Earth's only proper natural satellite. It is the fifth largest satellite in the Solar System, larger than any dwarf planet and the largest natural satellite in the Solar System relative to the size of its planet, at a quarter the diameter of Earth, comparable to the width of Australia.[13] The Moon orbits Earth at an average lunar distance of 384,400 km (238,900 mi),[14] or 1.28 light-seconds. Its gravitational influence produces Earth's tides and slightly lengthens Earth's day. The Moon is a differentiated rocky body; has a surface gravity of 0.1654 g, about one-sixth of Earth's; and lacks a significant atmosphere, hydrosphere or magnetic field. A planetary-mass moon, it has among satellites with a known density the second highest surface gravity and density in the Solar System after Jupiter's moon Io. The Moon's orbit around Earth has a sidereal period of 27.3 days, and a synodic period of 29.5 days. The synodic period drives its lunar phases, which form the basis for the months of a lunar calendar. The Moon is tidally locked to Earth, which means that the length of a full rotation of the Moon on its own axis (a lunar day) is the same as the synodic period, resulting in its same side (the near side) always facing Earth. That said, 59% of the total lunar surface can be seen from Earth through shifts in perspective (its libration).