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What is an astronomical unit?
An astronomical unit is the distance from the Earth to the Sun. This is equal to 149 million kilometers (93 million miles). This unit of measurement is used most often for planets that are within our solar system. For example, astronomers measured Pluto as being on average 39.47 AU from the sun. This means that its level of orbit is 39.74 times the distance from the Sun as the Earth is on average.