2. Space is really big! How do scientists measure distances in space?

3. The Problem Objects in our solar system are very far apart. Using kilometers or miles is not practical. For example, the distance from the Earth to the Sun is 149,597,870 km or 92,955,807 miles. Big numbers like that are hard to use.

5. The Solution To solve this problem, scientists created a new unit of measurement: an astronomical unit (AU). An AU is the average distance between the Earth and the Sun. More precisely it is 149,597,870,700 meters. So we call the distance between the Earth and the sun 1 AU.

6. The Next Problem Objects in the universe are even farther apart. Neptune is 30.07 AU from the Sun. The Oort cloud is 100,000 AU from the Sun. The next closest star to our solar system, Proxima Centauri, is 250,000 AU from the Sun. The numbers are getting big again and we haven’t gotten very far in the universe.

8. The Next Solution Scientists solved this problem in a similar way to the first problem, by making a new unit of measurement: a light year. A light year is the distance light travels in one year. 1 light year = 63,239 AU

9. If you would like to do the math: There are 60 seconds in one minute. There are 60 minutes in one hour (360 seconds). There are 24 hours in one day (8640 seconds). There are 365.25 days in a year (3,155,760 seconds). The speed of light in space is 299,792 kilometers per second. So light travels 946,071,601,900 kilometers in one year. It is much easier to just say 1 light year.

10. Kilometers and miles – to measure distances here on Earth. AU – to measure distances in our solar system. Light years - to measure distances in the universe. So this is how we measure distances:

11. Sources http://idlethumb.files.wordpress.com/2011/03/universe.jpg http://www.innerus.org/wp-content/uploads/2011/12/Universe.jpg http://www.space.com/17081-how-far-is-earth-from-the-sun.html http://www.nasa.gov http://nineplanets.org/planetorder.JPG