Astronomical unit (AU)

Definition

An astronomical unit (AU) is the average distance between the Earth and the Sun, approximately 149.6 million kilometers (93 million miles). It is commonly used to describe distances within our solar system.

5 Must Know Facts For Your Next Test

1. 1 AU is defined as 149,597,870.7 kilometers.
2. The concept of an astronomical unit was first proposed by Johannes Kepler.
3. It is used as a baseline for measuring distances to other planets in our solar system.
4. 1 AU represents the semi-major axis of Earth's orbit around the Sun.
5. The value of 1 AU can vary slightly due to orbital eccentricity.

Review Questions

Related terms

Kepler's Laws:

Three laws describing planetary motion, formulated by Johannes Kepler.

Semi-Major Axis: The longest diameter of an ellipse, half of which defines 1 AU for Earth's orbit.

Eccentricity:

A measure of how much an orbit deviates from being circular.