This is a drawing of Pluto and its moon Charon.
Click on image for full size
Image courtesy of NASA/JPL. This image is in the public domain.
AU stands for Astronomical Units. Distances in space are too large to measure in Earth standards like miles or kilometers. For distances too large to measue in AU, we use light years. A light year is the distance light moves in one year.
To be exact, an AU is the distance between the Earth and the Sun, which is 1.0 x 10^9 km, or about 93 million miles. For reference, Mars is 1.5 AU from the sun, Jupiter is 5 AU from the sun, Pluto is about 39 AU from the Sun, the heliopause is about 100 AU away, and the Oort Cloud is about 100,000 AU.
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