The Universe _______________________________________________________________________________________________________________________________________________________________________________________________________________________
6. Light-year and Parsec
We need a really big unit to measure distances out in space because distances between stars are so great.
A light-year, 9,5 trillion kilometres is the distance that light travels in one year. That’s a long way! Out in space, it’s actually a pretty short distance.
A parsec (pc) is equals to 3,26 light-years or roughly 31 trillion kilometres. Multiples of parsecs are used to express the distances at which very distant objects in the Universe are, for example the megaparsecs (Mpc).
Proxima Centauri is the closest star to us after the Sun. This near neighbour is 4,22 light-years away. That means the light from Proxima Centauri takes 4,22 years to reach us.
Our galaxy, the Milky Way Galaxy, is about 100,000 light-years across. So, it takes light 100.000 years to travel from one side of the galaxy to the other! It turns out that even 100.000 light years is a short distance.
The most distant galaxies we have detected are more than 13 billion light-years away. That’s over a hundred-billion-trillion kilometres!
This video will show you some basic facts about distances in the Universe