= Distance =

== Astronomical Unit ==

Abbreviated as AU, au, a.u., or sometimes ua

A unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometers (93 million miles).

== Light-year ==

Symbol: ly

 * exactly 9,460,730,472,580.8 km (about 10 Pm)
 * about 5,878,630,000,000 international miles
 * about 63,241.1 astronomical units
 * about 0.306601 parsecs

== Parsec ==

The parsec ("parallax of one arcsecond", symbol pc) is a unit of length, equal to just under 31 trillion kilometres (about 19 trillion miles), or about 3.26 light-years. The parsec is used in astronomy. The parsec is defined as the length of the adjacent side of an imaginary right triangle in space. The two dimensions that form this triangle are the parallax angle (defined as 1 arcsecond) and the opposite side (which is defined as 1 astronomical unit (AU), the distance from the Earth to the Sun). Given these two measurements, along with the rules of trigonometry, the length of the adjacent side (the parsec) can be found.