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What may have been a far more uncommon term 50 years ago has now become far more understood. For this, we can thank the media, teachers, and even Toy Story’s Buzz Lightyear. But what exactly is a light-year? 

A light-year is a term we use to describe the distance to most space objects. A light-year is the distance light travels in one Earth year: 6 trillion miles, or for those with more visual learning preferences, that is 6,000,000,000,000 miles. 

We know that light travels at a speed of 186,000 miles per second. While this does sound extremely fast, objects in space are so far away that it takes a lot of time for that light to reach us. When we use telescopes to look at distant objects in space, we are actually looking back in time. The farther an object is, the farther in the past we see it. Because light takes time to travel to our eyes, we know that everything we view in the sky has already happened. So something that is one light-year away, you see as it was one year ago.

For example, our Sun– the closest star to Earth– is about 93 million miles away. The Sun’s light takes about 8.3 minutes to reach the Earth. This means that we see the Sun as it was about 8.3 minutes ago. So when the Sun rises, it actually “rose” 8.3 minutes ago; it just took the light a little longer to get to us. 

Why Do We Measure Space In This Way?

While the distance of a light-year might seem a bit extreme, the enormous scale of the universe makes a light-year look minuscule in comparison. In contrast, measuring in miles or kilometers at an astronomical level would be completely impractical. 

Using light-years to determine the distance of objects in space and their relation to the past helps scientists to understand our early universe and the billions of galaxies around us. 

Fun Facts:

  • Our closest neighboring star is Proxima Centauri at 4.3 light-years away.
  • The North Star, Polaris, is 320 light-years away from the Earth.
  • Our Milky Way is 26,000 light-years away from the center of our galaxy.
  • Our closest neighboring galaxy, Andromeda, is 2.5 million light-years away from Earth.
  • One of the oldest galaxies ever found is called GN-z11, which is 13.4 billion light-years away. This galaxy was one of the first to form in the universe after the big bang.