Department of Physics

User's Guide to the Night Sky

Motion of the Inner Planets

The animation shows the inner solar system as seen from a viewpoint high above the plane of the solar system in a northwards direction. This is effectively high above the Earth's north pole. As seen from this observing viewpoint the planets orbit anticlockwise. From the Sun, the planets are Mercury, Venus, Earth and Mars. The closer the planet is to the Sun the faster it orbits. Relative to the distant stars the orbital periods of Mercury, Venus, Earth and Mars are 87.97 days, 224.70 days, 365.25 days (1 year) and 1.881 years respectively. The animation repeats after one synodic period of Mars, i.e. 780 days.

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