Light Speed
Astronomers measure the distance of stars using a constant speed standard. This is the speed of light in empty space.
Speed of light 299,792,458 meters per second (186,000 miles per second)[1]
Wow! Think how fast that is!
One light year is the distance that light travels in one year. 1 Light year is equal to about 10 trillion kilometers or 6 trillion miles![1]
The Sun is about 8 light minutes away. The next closest star to us is Alpha Centauri which is 4.2 light years away.[2]
Our galaxy, The Milky way is about 100,000 light years across![3]
Question How many kilometres is Alpha Centauri from us? Why is it a lot easier to use light years?
References
[1]Arny, Thomas T. (2006) Explorations: An Introduction to Astronomy, Fourth Edition , The McGraw-Hill Companies, Inc. pp9, ISBN 0-07-302580-1.
[2]http://en.wikipedia.org/wiki/List_of_nearest_stars
[3]Arny, Thomas T. (2006) Explorations: An Introduction to Astronomy, Fourth Edition , The McGraw-Hill Companies, Inc. pp10, ISBN 0-07-302580-1.