1. Characteristics of Stars

2. What is a galaxy? It is a cluster of stars (hundreds of billions of stars) It is a cluster of stars (hundreds of billions of stars) Our solar system is located in the Milky Way Galaxy Our solar system is located in the Milky Way Galaxy * Our galaxy is named the Milky Way because of it’s white milky color. Not because of the candy bar!!!!

3. What is the Universe? All of space and everything in it!!!! All of space and everything in it!!!! Consists of billions of galaxies. Consists of billions of galaxies. Most of the Universe is empty space, due to everything being soooooo far apart! Most of the Universe is empty space, due to everything being soooooo far apart!

4. Distances to Stars Instead of using kilometers, astronomers use a unit called light-year. Instead of using kilometers, astronomers use a unit called light-year. A light year is the distance light travels in one year or 9.5 million million kilometers. A light year is the distance light travels in one year or 9.5 million million kilometers. * If we wanted to travel to the center of the Milky Way it would take 25,000 years traveling at the speed of light. That is a distance of 250 million billion kilometers.

5. Measuring Distances to Stars Parallax- apparent change in position of an object when you look at it from different places. (Thumb example) Parallax- apparent change in position of an object when you look at it from different places. (Thumb example) Astronomers use the parallax shift to measure distance to stars: Astronomers use the parallax shift to measure distance to stars: First they observe a star & then observe it again 6 months later. First they observe a star & then observe it again 6 months later. The less the star moved the further away it is The less the star moved the further away it is The more the star moved the closer it is The more the star moved the closer it is

6. Classifying Stars Three main characteristics: Three main characteristics: Size Size Temperature Temperature Brightness Brightness

7. Size

8. Color & Temperature A star’s color reveals its temperature: A star’s color reveals its temperature: Stars that are red are the coolest (3,200 degrees Celsius) Stars that are red are the coolest (3,200 degrees Celsius) Betelgeuse Betelgeuse Stars that glow blue-white are the hottest (15,000 degrees Celsius) Stars that glow blue-white are the hottest (15,000 degrees Celsius) Rigel Rigel

9. Brightness Brightness of a star depends on its temperature and size. Brightness of a star depends on its temperature and size. How bright a star is also depends on its distance from Earth. How bright a star is also depends on its distance from Earth. Brightness is described in two different ways: Brightness is described in two different ways: Apparent magnitude Apparent magnitude Absolute magnitude Absolute magnitude

10. Brightness Apparent Magnitude- Apparent Magnitude- Brightness as seen from Earth. Brightness as seen from Earth. Ex. Sun looks very bright but this does not mean the sun gives off more light than other stars. It just means it is closer to Earth. Absolute Magnitude Absolute Magnitude Brightness a star would have if it were at a standard distance from Earth Astronomers determine the apparent magnitude and distance from Earth in order to calculate the absolute magnitude Astronomers determine the apparent magnitude and distance from Earth in order to calculate the absolute magnitude

11. Hertzsprung-Russell Diagram