Astronomical Unit (AU)
1 AU = 1.50 x 1011 m
This is the average distance of the Earth from the sun.
Light year (lyr)
1 lyr = 9.46 x 1015m
The is the distance travelled by light in a vacuum in one year.
A light year is 5.9 x 1012 miles (approx 6 trillion miles).
1 pc = 3.08 x 1016 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