Q: What's a Megaparsec?

A: A million parsecs, of course.

Q: OK, so what's a parsec?

A: A madeup word ("parallax" + "arcsecond")
and a geometrical measurement of distance
commonly used by astronomers

distance (in parsecs) = 1/p (in arcseconds)

1 arcsecond = 1/3600 degree = 1/206265 radian

1 parsec = 3.26 light years

closest stars are a few parsecs away
closest large galaxy (Andromeda) is about 0.75 Mpc away

Note: "p" is only measureable for relatively close objects (currently this means d < 500 pc); "p" cannot be directly measured for galaxies and other methods of distance measurement must be employed.

Back to Cosmological Principle or back to start.