Explore how astronomers and scientists use astronomical units to measure distances in the solar system in this video adapted from NASA. The astronomical unit (au) -- equal to the average distance from Earth to the Sun -- is a convenient unit of measure when talking about distances in the solar system. The video describes how to use proportions to calculate the distance from Mars to the Sun in miles when given its distance in astronomical units. Viewers are asked to estimate the distance in astronomical units to the Voyager 1 spacecraft position, as of 2003, when given its distance in miles and kilometers.