Astronomical Unit (AU)

7.6 - Be able to use the astronomical unit (1 AU = 1.5 × 108 km)...

The Earth rotates around the Sun in an elliptical orbit. This means it orbits in a slight oval shape.

At some point in the year it is nearer the Sun, at another point it is further away. We therefore make an average.

The mean average distance from Earth to the Sun is 149,600,000 km.

This is called 1 Astronomical Unit, or AU. This figure is a standard number in astronomy. Many distances to planets and stars are calculated using this number.

It is normally rounded to 150,000,000 km.


  • What is the AU?
  • How many km is the AU?
  • Why is this number important to astronomers?
Did you know?

The shape of Earth's orbit does not contribute to our seasons. Seasons are caused by the tilt of Earth's axis.


Imagine at NASA Calculate the AU