Astronomy and Space Science
Chapter 4: Stars, Galaxies, and the Universe
Lesson 3: Characteristics of Stars
**My Planet Diary**
- Complete the My Planet Diary on your own. It is located on page 136 of your textbook.
How are Stars Classified?
 Characteristics used to classify stars include color, temperature, size, composition, and
brightness
- Color and Temperature
~ Red Stars= Surface Temperature is about 3,200°C (coolest stars)
~ Yellow Stars= Surface Temperature is about ________________
~ ____________________= Surface Temperature is about 20,000°C
- Size
~ stars are farther away than the sun so that is why
they look smaller than the sun
~ Giant stars or super giant stars= Very large Stars
~ White Dwarf stars= about the size of _________
~ Neutrons= about _________________________
** Complete Figure 1 on Page 137**
- Chemical Composition
~ Most stars= 73% hydrogen, 25% helium, and 2% ____________________
- Spectograph= ______________________________________________________
~Breaks light into colors and produces an image of the resulting spectrum
** Complete “apply it” on P. 138 in your book**
Brightness of stars
- brightness of a star depends upon both its ___________ and ___________________
~ large stars= tends to be brighter
~ hotter stars tend to be brighter than a cooler star
- ____________________________= a stars brightness as seen from earth
- Absolute Brightness= ________________________________________________
________________________________(if all stars were the same distance from earth)
What is an H-R Diagram and How Do Astronomers Use it?
 Hertzsprung-Russell Diagram (H-R diagram)= shows how surface temperature of stars and
absolute brightness are related on a graph
 Astronomers use H-R Diagrams to classify stars and to understand how stars change over time
More than ____% of stars are main sequence stars (surface temp increases as absolute
brightness increases)
** Complete Assess Your Understanding on p. 141 of your textbook**