Light Year (ly)
This is the distance that light travels in one year.  Since light travels an amazing 300 000 kilometers in 1 second and since there are about 31 million seconds in a year, simple math (distance = speed X time) tells us that one ly = 9.5 trillion kilometres!!  More precisely and using scientific notation, 1 ly = 9.468 x 1015 m.

Distances and Light-Travel Times
One very useful aspect of the ly as a unit of distance is the fact that we can immediately deduce the time required for light to traverse that distance.  Since, for example, M31 or the Andromeda galaxy is 2.2 million light years away we know that the light reaching your eye is 2.2 million years old!  As you will learn in future lectures, Einstein's theory of relativity teaches us that the speed of light is the upper speed limit for any body in the universe.

In my Colt ....
This is NOT a good idea.  At a cruising speed of  100 km/h  or 100km/3600 s = 0.028 km/s, it will take me  about 23 trillion years to get there!!  As you will learn, this is many times older than the entire universe itself.  Simply put - the universe is enormous!
(Math details:  time = distance/speed, so time = (2.2 Mly x 9.5 trillion km)/(0.028 km/s) = 7.5 x 1020 s)