Planets

The planets are spherical bodies which rotate around the hub of the earth with the Sun. Five planets — Mercury, Venus, Mars, Jupiter, and Saturn are visible to the naked eye and were known to the ancients as "wandering stars;" entities which appear to move differently from the fixed path of the stars. The word "planet" comes from the Greek word planetes, meaning "wanderer."

Topics

• Discovery of Neptune
• Precession of Mercury's Orbit
• Kings Dethroned
• Astronomical Prediction Based on Patterns
• Three Body Problem

Dance of the Planets

The planets move around the earth along the ecliptic, with an apparent relationship to the Sun. Mercury and Venus appear to be rotating around the Sun, while the other planets have a less direct effect.

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The Copernican Revolution of the 16th century held that this relationship with the Sun was evidence that all of the planets of the Solar System moved around the Sun. While it may be that the planets move with a relationship to the sun, from this it does not necessarily follow that the Earth is a planet. At the time the idea of a Round Earth was widely prevalent, based on the teachings of the Ancient Greeks. It was deduced that since the Earth is a round body in a Sun-centered celestial system, that the earth must be a body in motion similar to the planets seen in the sky.

  “ I demonstrate by means of philosophy that the earth is round, and is inhabited on all sides; that it is insignificantly small, and is borne through the stars. ” ⁠— Johannes Kepler

Prediction in Astronomy

Prediction in astronomy is performed through patterns. By analysis of historic tables it is possible to construct functions which can predict where a planet will be in the future. This is how prediction in astronomy has been performed since times of antiquity, and how it is performed today. See: Astronomical Prediction Based on Patterns