Astronomical unit

Definition

An astronomical unit (AU) is a unit of distance defined as the average distance between 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 approximately equal to 149.6 million kilometers or 93 million miles.
2. The astronomical unit was derived from the average Earth-Sun distance, making it a convenient measure for interplanetary distances.
3. The concept of AU has been standardized by the International Astronomical Union (IAU).
4. Distances to planets in our solar system are often expressed in AUs for simplicity.
5. 1 AU is also used as a baseline for measuring parallax and determining distances to nearby stars.

Review Questions

• What is the numerical value of an astronomical unit in kilometers?
• Why is the astronomical unit useful in astronomy?
• How was the astronomical unit originally defined and who standardized it?

Related terms

Light Year: A light year is the distance that light travels in one year, approximately 9.46 trillion kilometers or about 5.88 trillion miles.

Parsec:

A parsec is a unit of distance used to measure large astronomical distances, equivalent to about 3.26 light years or roughly 31 trillion kilometers.

Parallax:

Parallax refers to the apparent shift in position of an object when viewed from different perspectives, commonly used to measure distances to stars.