HR Diagrams HR Diagrams

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

TemperatureTemperature

The physical properties used on the H-R diagram The physical properties used on the H-R diagram are are temperature, absolute magnitude, and colortemperature, absolute magnitude, and color. . Stellar temperature is generally recorded using the Stellar temperature is generally recorded using the Kelvin scale. Kelvin scale. A temperature recorded using the A temperature recorded using the Kelvin scale is the temperature in Celsius + 273.Kelvin scale is the temperature in Celsius + 273. This method avoids negative temperatures. Surface This method avoids negative temperatures. Surface temperature determines the color of a star.temperature determines the color of a star.

Stellar Temperature-Color Relationship

blue blue white white yellow white yellowReddishorange

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

BrightnessBrightness Absolute magnitudeAbsolute magnitude is the measure of light stars is the measure of light stars

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

Scientists classify stars according to: _______, _______, & ________

A star’s color reveals its __________. The coolest stars glow ______, while the hottest stars glow ___________.

SIZE

BLUERED

BrightnessTemperature

Temperature

Types of StarsTypes of StarsClassificationClassification

Class Temperature Color

O 20,000- 60,000 K Blue

B 10,000 – 30,000 K Blue-white

A 7,500 – 10,000 K White

F 6,000 – 7,500 K Yellow-white

G 5,000 – 6,000 K Yellow

K 3,500 – 5,000 K Orange

M 2,000 – 3,500 K Red

Q: Based on its color, is our sun very Q: Based on its color, is our sun very hot? hot? ______________________

______________________ of a star depends on its of a star depends on its ______________________ and and ____________________. .

Brightness can be measured in terms of Brightness can be measured in terms of _____________or in______________._____________or in______________.

NO

SIZE TemperatureBrightness

luminosity magnitude

__________________________ is is the measure of the measure of light stars generate light stars generate from their surface. from their surface. An incredibly An incredibly bright star has a bright star has a magnitude of magnitude of -5-5 or or more, an average more, an average star’s magnitude is star’s magnitude is close to close to 11, and a , and a dim star’s dim star’s magnitude is magnitude is around around 1010. .

__________ is how much power the star gives off as compared to our Sun. Our sun’s luminosity is 1.

LuminosityMagnitude