Distances in space are enormous - so big that our standard units of measurement, kilometres and miles, are just too small to be useful.
So scientists use something else - the light year.
But what is it and how does it work?
Dr Tim O'Brien from the Jodrell Bank Centre for Astrophysics at the University of Manchester explains.
Please note: The graphics used in this video are not to scale
Images courtesy of Nasa
3 February 2010

Song: Ryan Farish - Walk with You ( http://www.ryanfarish.com/ ),
Source of Images: NASA A.p.o.d. Archive ( http://apod.nasa.gov/apod/archivepix.html )

See the most fascinating universe images available. To ensure that you get the best delivered, i looked up more than a thousand images and used only the very best of them.

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Carl Sagan told us that there are more stars in the universe than there are grains of sand on all of the Earth's beaches. At the same time, there are more H2O molecules in just 10 drops of water than there are stars. 

Ranging from the unimaginably small to the unimaginably big, the scale of the universe is mind-boggling. Watch to try to wrap your head around it. 

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How Big Is The Universe?

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