"astronomical unit." YourDictionary, n.d. Web. 11 October 2018. <http://www.yourdictionary.com/astronomical-unit>.
astronomical unit. (n.d.). Retrieved October 11th, 2018, from http://www.yourdictionary.com/astronomical-unit
A unit of length used in measuring astronomical distances within the solar system or other planetary system equal to the mean distance from Earth to the sun, approximately 150 million kilometers (93 million miles).