Astronomical Unit (AU)
An astronomical unit (AU) is a unit of length, roughly the distance from Earth to the Sun. It is defined as exactly 149,597,870.7 kilometers (92,955,807.3 miles). The astronomical unit provides a convenient way to express distances within the solar system and is commonly used in space and astronautical engineering. It is also used as a reference point for measuring distances to other stars and galaxies. The concept of the astronomical unit was developed by ancient astronomers who observed the motion of the planets and their distances from Earth. Today, it is used in spacecraft navigation and in calculating the trajectories of space probes and satellites.
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