Discovery and exploration of the Solar System Discovery and exploration of the Solar System Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets including Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust. For many thousands of years, astronomers maintained a geocentric world view and did not recognize the existence of a Solar System. Most believed Earth was stationary at the center of the Universe and categorically different from the divine or ethereal objects
Moon to the planet's equatorial plane. The Moon's orbit is subtly perturbed by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon's orbit gradually rotates once every 18.61 years, which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws. The Moon is exceptionally large relative to Earth: Its diameter is more than a quarter and its mass is 1/81 of Earth's. It is the largest moon in the Solar System relative to the size of its planet, though Charon is larger relative to the dwarf planet