Distance continued

This page continues from here.

Light years also provide some helpful info on solar system distances: the Sun is about 8 light minutes from Earth. (And yes, there are also light seconds!) And because light from objects travels at light speed, when you see the Sun, or Jupiter or a distant star, you're seeing it as it was when the light left it, be that 8 minutes, tens of minutes or 4.3 years ago. And this is fundamental to the idea that when we're looking farther out into space, we're seeing farther back in time. (Think about it: you're seeing all the stars in the sky at different times in history — some a few years ago, others hundreds of years ago — all at the same time!)
 
Finally, parsecs. This is the unit used when the number of light years between objects climbs into the high thousands or millions. 
 
One parsec is 3.26 light years. The origin of this unit of measure is a little more complicated, but it's related to how astronomers measure widths in the sky. Astronomers use "megaparsecs" — a megaparsec is 1 million parsecs — for intergalactic distances, or the scale of distances between the galaxies.
 
And at the point when distances between galaxies become so large that even megaparsecs are less used, astronomers talk about distances in terms of how much a galaxy's light has been shifted toward longer, redder wavelengths by the expansion of the universe — a measure known as "redshift." Now that's astronomical!.