1 AU or astronomical unit is the average distance from the Earth to Sun. So 1AU is 149,598,000 kilometers or 92,955,000 miles.
Astronomers use this method of measurement because the distances in the Solar System are so vast. It takes about 8 minutes for light to travel the distance from the Sun to the Earth, and light is moving at 300,000 km per second.
For example, the distance from Sun to Mercury is an average of 0.387 AU. And the distance from the Sun to Jupiter is 5.204 AU. The distance to the Oort Cloud is approximately 50,000 AU, and the distance to the nearest star is about 250,000 AU.
To measure longer distances in the Universe, astronomers switch to light years. A light year is the distance that light travels in a single year and works out to be 63,239 AU. If that’s not enough, they use another term called parsecs. 1 parsec is equivalent to 3.26163626 light years.
If you’d like more information about the Earth’s orbit, check out this explainer from NASA.
We’ve also recorded an entire episode of Astronomy Cast all about distances in astronomy. Listen here, Episode 10: Measuring Distance in the Universe.