What is a light year?
A lightyear is defined as the distance light would travel in a vaccuum in one year. It is approximately 10 trillion kilometers or 5,865,696,000,000 miles.
What is a MegaParsec (Mpc)?
In cosmology, distances are often measured in units of megaParsecs, which are 3.26 million light-years. A megaParsec is abreviated Mpc.
Just as the name implies, the megaparsec is a million parsecs. The parsec is defined as the length of the adjacent side of an imaginary right triangle in space. In this imaginary triangle, the included angle is defined to be 1 arcsecond and the opposite side is defined to be the distance between the Earth and the Sun. This definition came about from the astronomical method of measuring the distance to relatively close objects by measuring this included angle as a parallax angle. A parsec is approximately 19 trillion miles and is abreviated pc.
