Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
September 14, 1995
The Far Side
Credit: The Soviet Lunar Program
Why does the Moon have a far side? Gravitational tidal forces within the Earth-Moon system have synchronized the Moon's period of rotation around its axis with its orbital period at about 28 days. So, as the Moon moves around its orbit its rotation exactly compensates, keeping the same face toward the Earth.
Authors & editors:
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.