### Astronomical Unit (AU)

1 AU = 1.50 x 10^{11} m

This is the average distance of the Earth from the sun.

### Light year (lyr)

1 lyr = 9.46 x 10^{15}m

The is the distance travelled by light in a vacuum in one year.

A light year is 5.9 x 10^{12} miles (approx 6 trillion miles).

### Parsec (pc)

1 pc = 3.08 x 10^{16} m

One parsec (pc) is the distance to a star that subtends and angle of 1 arc second at an arc length of 1 AU.

How to calculate the distance in parsecs from the parallax angle in seconds.

d = distance in parsecs (pc)

J = the parallax angle in seconds