What’s a Light Year?

Did you know the nearest star to our sun is 24,942,474,700,000 miles away? The nearest galaxy is about 14,919,633,000,000,000,000 miles away? Those are enormous numbers that are difficult to even imagine or understand!

Proxima Centauri, Credit Hubble

This is why when scientists talk about the distance to nearest stars, they don’t use miles. Instead, they use a measurement known as a light year. Light is the fastest thing in the universe, traveling over 186,000 miles per second! Over the course of one year, it goes about 6 trillion (6,000,000,000,000!!!) miles. This is what we know as a light year.

Some things are still really far away even in light years, but it makes it much easier to compare and understand what things are astronomically close to or far away from us. With our new way of measuring, the nearest star is about 4 light years away. The Andromeda Galaxy is 2,560,000 light years away! That’s still a big number, but its easier to understand how much further away it is than the nearest star.

Andromeda Galaxy (Creative Commons/flickr)

Light years have another convenient and very cool meaning. Since the light from a star or galaxy has to get to the Earth for us to see us, it means that the light had to travel here! Looking at that light means that we are looking at the star the way it was 4 years ago. Looking out in space is actually looking back in time, which can teach us lots of things about our universe.

Looking at the Andromeda galaxy, we are looking at it the way it was over 2 million years ago! Using the Hubble telescope, we have been able to look out at galaxies that are over 13 billion light years away, allowing us to look back to very early in the universe.

Hubble Ultra Deep Field Credit NASA/ESA/Hubble

Watch this video that further illustrates the enormity of a light year!


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