One Astronomical Unit is the mean distance between the Sun and the Earth. The Earth's orbit is an ellipse, so sometimes Earth is less than 1 AU from the Sun, and sometimes it is a bit farther out.
The precise value of the AU is currently accepted as 149,597,870,000 meters, which is 93 million miles approximately.
So 8 AU is eight times that far. Google has a really neat calculator and conversion feature, so I typed "8 Astronomical Units in miles" into the Google search box and got this answer:
8 Astronomical Units = 743,647,101 miles
Pretty neat, huh?!?!