Actually the Earth/Moon system due to their relative sizes is considered a dual planetary system..the moon does not orbit the Earth. The Earth and Moon orbit the barycentre (centre of mass of the system--always below Earth's crust and always in motion). In astrology both Moon and Sun are considered planets. Another interesting thing about the Moon is that, although very bright seen from Earth, is one of the darkest (least reflective) bodies in the solar system. too much info?