1. Distances in Space Characteristics of Stars

2. Distances in Space Distances are vast Two scales are used
Cannot use miles or kilometers because the numbers are so large
Two scales are used
One scale for our solar system
Another scale for beyond our solar system

3. Astronomical Unit Used for measuring distances within our solar system
The distance from the Earth to the Sun (about 93 million miles)
1 AU

5. Light Year Light Year – the distance light travels in one year
Speed of light is ~ 186,000 miles per second
6 trillion miles
6,000,000,000,000 miles
Interesting fact – to count to
1 trillion – at 1 number per second
Would take you 31,687 years!!

7. Characteristics of Stars

8. Classifying Stars All stars are huge spheres of glowing gas
All are mostly Hydrogen
Produce energy through nuclear fusion

9. Classifying Stars
Stars are classified based on their physical characteristics
Color
Temperature
Size
Composition
Brightness

10. Color and Temperature A stars color reveals its temperature
Coolest stars are red
Medium temperature stars are yellow – white
Hottest stars are blue

11. Size Stars vary greatly in size Our sun is a medium sized star
Some are much larger – giants and supergiants
Many are smaller
White Dwarfs – about the size of Earth
Neutron Stars – only about 20 km wide (12 miles)

12. Star Sizes

18. Chemical Composition
A spectrograph determines the exact chemical composition of stars
Most are 73% Hydrogen and 25% Helium and 2% other elements

19. Brightness The brightness of a star depends two things
Size
Temperature
How bright a star looks from Earth depends on two things
Distance from Earth
How bright the star truly is

20. Apparent Brightness
Apparent Brightness – how bright a star appears from Earth
Closer stars tend to be brighter
Distance stars appear dimmer

21. Absolute Brightness
The brightness a star would have if it were a standard distance from Earth
Must know the apparent brightness and distance from Earth

22. Parallax
Parallax – the apparent change in position of an object when you look at it from different places
Thumb demo
Parallax is used to measure the distance to nearby stars (within a few hundred light years)

23. H-R Diagrams
A diagram showing the relationship between a stars surface temperature and absolute brightness
Shows how stars can change over time