What does one light year away mean?

How far is a light year?

The speed of light is used to describe the enormous distances in space. The distance of one light year is approximately 9,460,730,472,580.8 kilometers. This corresponds to a rounded 9.5 trillion km. So light travels a distance of around 9.5 trillion km in one year.

The speed of light is a so-called natural constant. Light moves in a vacuum at a speed of 299,792,458 meters per second. This corresponds to around 299,792 kilometers per second - roughly rounded: 300,000 km per second.

See also: Units and their prefixes (simple overview)

Measure distances with light

The distance that light travels in one second is roughly 8.5 times the circumference of the earth. The moon is approximately 384,400 km from Earth. Light that is reflected from the moon therefore needs a little more than a second before we see it on earth. The Sun is around 147 million km away. The light takes around 490 seconds to cover this distance, a little more than 8 minutes.

Which is the closest star to us after the sun Alpha Centauri (Strictly speaking, these are three stars). It is 4.36 light years away. Together with billions of other stars, we form a galaxy, the Milky Way. The next galaxy is the Large Magellanic Cloud - it is 160,000 light years away. And that's practically the next neighboring city. Thanks to the speed of light, we can describe the size of the universe, but it is unimaginable ...

From the light that has been moving through the universe for millions of years, one can draw interesting conclusions about the light source - with the help of spectral analysis or spectroscopy.

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