1. Solar System – Activity 11

2. What do all of these words mean? STARSUN SOLAR SYSTEM STAR A STAR is an extremely large, hot ball of burning gas that radiates light and heat. Scientists estimate that there are 200 billion stars in our galaxy alone! SUN The SUN is a star that the nine planets orbit around. SOLAR SYSTEM The SOLAR SYSTEM is the Sun and all of the satellites that orbit it. We live here!

3. NORTH STAR ALPHA CENTAURI Do you know another name for the North Star? Polaris! But, why Polaris?

4. The Sun is… kilometers from Earth. 149,600,000 Alpha Centauri is… 40,678,000,000 kilometers from Earth.

5. But, scientists don’t use kilometer (or miles) to measure distances in space. What do they use? Light years! What in the world is a light year? A LIGHT YEAR is the distance that light travels in one year. It is equal to… 9,460,000,000,000 km

6. STARDISTANCE FROM EARTH The Sun8 light seconds Alpha Centauri4.3 light years North Star (Polaris)300 light years Sirius8.7 light years Betelgeuse500 light years Rigel1,000 light years

7. Of all the stars you can see in the night sky, do you think the brightest stars are the closest stars? HYPOTHESIS Write your HYPOTHESIS down on your Activity 11 worksheet. “Yes, I think that the stars closest to us are the brightest.” “No, I do not think that the closest stars are always the brightest.”

8. Time to test our hypothesis!

9. What is our conclusion? Can we determine how far away a star is by how bright it is? Are the closest stars always the brightest? No, star’s brightness actually depends on it’s size and temperature (and also on where it is in it’s life span). Some stars are estimated to be 100,000 times brighter than our Sun!

10. Scattered through space are massive, swirling clusters of billions of stars. Do you know what such a cluster of stars is called? A galaxy!

11. So, if the universe contains trillions of galaxies and easy galaxy contains billions of stars, how many stars are there in the universe! Too many to count, but scientists estimate that there are 1 septillion! 1,000,000,000,000,000,000,000,000