Light Year

A light year is the distance that light travels in one year, which is about six trillion miles. While a light year is a measure of distance, it is also an indication that when we look out into space we do not see things as they are today. We see them as they were when the light that is reaching our eyes left the object we are looking at.

In the photo at left, taken by NASA’s Spitzer Space telescope, the individual bright stars are relatively “close,” only a few tens to hundreds of light years away. The galaxy, whose billions of stars are so far away that their light blends together into a pinkish and bluish haze, is 45 million light years away. That means that we see it as it was 45 million years ago.