1. HR Diagrams In the early 1900s, two scientists named Hertzsprung and Russell each discovered that there is a relationship between the brightness of stars and surface temperature. Although these scientists did not work together, the graph that illustrates their findings is named after them. In the early 1900s, two scientists named Hertzsprung and Russell each discovered that there is a relationship between the brightness of stars and surface temperature. Although these scientists did not work together, the graph that illustrates their findings is named after them.

3. Temperature The physical properties used on the H-R diagram are temperature, absolute magnitude, and color. Stellar temperature is generally recorded using the Kelvin scale. A temperature recorded using the Kelvin scale is the temperature in Celsius + 273. This method avoids negative temperatures. Surface temperature determines the color of a star. The physical properties used on the H-R diagram are temperature, absolute magnitude, and color. Stellar temperature is generally recorded using the Kelvin scale. A temperature recorded using the Kelvin scale is the temperature in Celsius + 273. This method avoids negative temperatures. Surface temperature determines the color of a star. Stellar Temperature-Color Relationship blueblue whitewhiteyellow whiteyellow Reddish orange red 25,000+  K 11,000- 25,000  K 7,500- 11,000  K 6,000- 7,500  K 5,000- 6,000  K 3,500- 5,000  K 2,000- 3,500  K

4. Brightness Absolute magnitude is the measure of light stars generate from the surface. Since stars are different distances from Earth, absolute magnitude is a measure of brightness regardless of distance. An incredibly bright star has a magnitude of –5 or more, an average star’s absolute magnitude is close to 1, and a dim star’s magnitude is around 10. In general, stars that are large and hot are brighter than those that are small and cool. Since stars change in predictable ways as they age, 85% of stars follow this general pattern called the Main Sequence. Most scientists consider an H-R diagram a snapshot of the lives of stars. Absolute magnitude is the measure of light stars generate from the surface. Since stars are different distances from Earth, absolute magnitude is a measure of brightness regardless of distance. An incredibly bright star has a magnitude of –5 or more, an average star’s absolute magnitude is close to 1, and a dim star’s magnitude is around 10. In general, stars that are large and hot are brighter than those that are small and cool. Since stars change in predictable ways as they age, 85% of stars follow this general pattern called the Main Sequence. Most scientists consider an H-R diagram a snapshot of the lives of stars.

5. Scientists classify stars according to: _______, _______, & ________ A star’s color reveals its __________. The coolest stars glow ______, while the hottest stars glow ___________. SIZE BLUE RED BrightnessTemperature

6. Types of Stars Classification ClassTemperatureColor O20,000- 60,000 KBlue B10,000 – 30,000 KBlue-white A7,500 – 10,000 KWhite F6,000 – 7,500 KYellow-white G5,000 – 6,000 KYellow K3,500 – 5,000 KOrange M2,000 – 3,500 KRed

7. Q: Based on its color, is our sun very hot? ___________ ___________ of a star depends on its ___________ and __________. Brightness can be measured in terms of _____________or in______________. NO SIZE Temperature Brightness luminositymagnitude

8. _____________ is the measure of light stars generate from their surface. An incredibly bright star has a magnitude of -5 or more, an average star’s magnitude is close to 1, and a dim star’s magnitude is around 10. _____________ is the measure of light stars generate from their surface. An incredibly bright star has a magnitude of -5 or more, an average star’s magnitude is close to 1, and a dim star’s magnitude is around 10. __________ is how much power the star gives off as compared to our Sun. Our sun’s luminosity is 1. Luminosity Magnitude