<P> The astronomical unit ( symbol : au , ua , or AU ) is a unit of length , roughly the distance from Earth to the Sun . However , that distance varies as Earth orbits the Sun , from a maximum ( aphelion ) to a minimum ( perihelion ) and back again once a year . Originally conceived as the average of Earth 's aphelion and perihelion , since 2012 it has been defined as exactly 7011149597870700000 ♠ 149 597 870 700 metres or about 150 million kilometres ( 93 million miles ) . The astronomical unit is used primarily for measuring distances within the Solar System or around other stars . However , it is also a fundamental component in the definition of another unit of astronomical length , the parsec . </P>
<P> The astronomical unit ( symbol : au , ua , or AU ) is a unit of length , roughly the distance from Earth to the Sun . However , that distance varies as Earth orbits the Sun , from a maximum ( aphelion ) to a minimum ( perihelion ) and back again once a year . Originally conceived as the average of Earth 's aphelion and perihelion , since 2012 it has been defined as exactly 7011149597870700000 ♠ 149 597 870 700 metres or about 150 million kilometres ( 93 million miles ) . The astronomical unit is used primarily for measuring distances within the Solar System or around other stars . However , it is also a fundamental component in the definition of another unit of astronomical length , the parsec . </P>
the mean distance between the earth and the sun is called the
the mean distance between the earth and the sun is called the
astronomical unit
astronomical unit