| A light-year is the distance light travels in one Earth year | The universe is filled with billions of galaxies, all farther away than this |
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| Binney, James; Tremaine, Scott 2008 | Looking Back in Time When we use powerful telescopes to look at distant objects in space, we are actually looking back in time |
Illingworth University of California, Santa Cruz.
| Princeton, NJ: Princeton University Press | This seems really fast, but objects in space are so far away that it takes a lot of time for their light to reach us |
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| All of the other stars we can see with our eyes are farther, some even thousands of light-years away | For most space objects, we use light-years to describe their distance |
Professor suggests parsec, which may be taken as an abbreviated form of 'a distance corresponding to a parallax of one second'.
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