Astonomy Vocabulary

Apogee

Perigee

Aphelion

Periphilion

AU – The ASTRONOMICAL UNIT

is a unit of length which is approximately equal to the distance of the Earth from the Sun. One astronomical unit is equal to 149.6×109 m, 15.81×10-6 light years, or 4.848×10-6 parsecs.

The astronomical unit is used almost universally for measuring distances between bodies within our Solar System, and when discussing the sizes of planetary systems around other stars. For example, Jupiter orbits the Sun at an average distance of 5.2 AU.

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