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Light Years


Light Years…Are they years of light, or light of a year? What are they? What is for certain is that light years are very important in trying to gauge and measure the distance to and from everything that exists in the universe.

Scientists have come up with this measurement as a way of basically measuring the universe in a unit of measurement that can make as simple as sense as possible.

The below picture represents stars within 13 light years of the sun.


A light year is an astronomical measurement of the distance that light can travel in 1 year. Hence the name ‘Light Year’


So what is the distance in miles that light can travel in a year, making up a light year. The distance is 6 trillion miles. That’s 6 million million miles.


So, it’s right that astronomers measure distances between any objects in the universe in light years as the universe is so vast. To give you an example: The closest star to Earth and our own star, the Sun, is a star called Proxima Centauri, that is 4.25 light years away. Or 4.25 x 6 trillion miles. So that is 25.5 trillion miles away, and that’s the closest star. So you see, it would get complicated and would really just take too much time spell out the distance between things in this vast universe. 


Just the nearest galaxy Andromeda is 2.5 million light years away. That’s a trillion trillion trillion trillion trillion…. It’s too many trillions. You get the picture. So to measure in light years and to work it out that way is much better and easier for all involved.   


So remember, a light year is a unit of distance rather than a unit of time, even though time is important to the measurement.


There are other units of measure for the universe, however we are good for now with light years. !!


Kids Fun Facts Corner

# 1. The Milky Way galaxy is over 100,000 light years across.

# 2. The local group of galaxies is over 10 million light years across.

# 3. The Virgo supercluster is over 110 million light years across.

# 4. The Laniakea supercluster is over 520 million light years across.

# 5. The observable universe is 93 billion light years across.


Q&A Corner

Q. What is a light year?

Q. What is the distance in miles of a light year?

Q. How many light years away from Earth is the closest star Proxima Centauri?

Q. How many light years away from Earth is the closest galaxy Andromeda?

Q. How many billion light years across is the observable universe? 

Download questions about light years here: light years (answers are on this page)

For further reading and more info on light years visit

Key Vocabulary Universe. Galaxy. Sun. Earth. Light. Year.


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