1. Stars
A self-luminous celestial body consisting of a mass of gas held together by its own gravity in which the energy generated by nuclear reactions in the interior is balanced by the outflow of energy to the surface, and the inward-directed gravitational forces are balanced by the outward-directed gas and radiation pressures

2. Massive luminous balls of plasma held together by gravity
Stars
Massive luminous balls of plasma held together by gravity

3. Characteristics of Stars
Color
Temperature
Mass
We use these characteristics to understand and examine stars

4. Color Color is a clue to a star’s temperature.
Blue stars are hotter/ newer/closer
Red stars are cooler/older/more distant

5. b. Temperature Very hot stars emit short-wavelength light BLUE
Cooler stars emit long-wavelength light
RED

6. c. Mass - A unified body of matter with no specific shape
Mass is how much “stuff” is squeezed into a space

7. Japan subway car without much “stuff” inside =
Less Mass

8. Crowded Japan subway car with lots of “stuff” = More mass
Lots of “stuff” squeezed into a space, place or thing

9. Binary Stars – pairs of stars pulled toward each other by gravity
Many stars orbit each other
More than 50% of stars occur in pairs or multiples.
Binary stars are used to determine the star property most difficult to calculate – It’s mass

10. If the sizes of the orbits are known
Then the stars mass can be determined

11. Hertzsprung-Russell Diagram
Shows the relationship between the absolute magnitude and the temperature of stars
90 % main-sequence stars
Giants
Supergiants
White dwarfs

12. Light Year – the distance light travels in 1 year
9.5 x 10 to the 12th power Or
9.5 trillion kilometers
miles per second
Distances to stars are so large that units like miles or kilometers are too hard to use
The numbers get really, really confusing and big

13. Measuring distance to stars – it’s difficult
The most basic way to measure distance to stars is parallax.

14. Parallax – the slight shifting of a nearby star due to the orbital motion of Earth
uses photographs of stars to compare to distant stars in the background shifting angles are compared the angles compared are very small
Close stars = large parallax angles
Distant stars = smaller parallax angles

15. Apparent Magnitude - a stars brightness as it appears from Earth
3 factors control the brightness from Earth
How big
How hot
How far away

16. Absolute Magnitude – how bright a star actually is

17. Variable Stars – some stars fluctuate in brightness
Cepheid – gets brighter in a variable pattern
Nova – sudden brightening of a star due to a flare up

18. Interstellar Matter - between existing stars is “the vacuum of space”
Except for Nebulae…

19. Nebulae – clouds of dust, gas, and thinly scattered matter
Stars and planets form from this interstellar matter
Nebulae begin to contract
Gravity squeezes particles in the nebula towards the center
Nebula shrinks
Gravitational energy is converted into heat energy

20. Protostar Stage – a developing star not hot enough to begin nuclear fusion
Contraction lasting million years
Collapse causes the core to heat more than the outer layer
Causes gas to increase it’s motion
When the core reaches 10 million K, nuclear fusion of hydrogen begins
A star is born

21. Main-Sequence Star – a star balanced between 2 forces, gravity and gas pressure
Gravity(external force)
Gas (internal force)
Hydrogen fusion lasts a few billion years
90% of an average stars life is in this hydrogen burning stage
When a star’s hydrogen fuel in the core is depleted, it evolved rapidly and dies.
Some stars delay death by burning heavier elements and become giants

22. Gravity (external force)
Gas (internal force)

23. Red Giant Stage
Inner Core consumes all hydrogen fuel energy and begins to contract
Helium core is left behind
Core contracts and heat is radiated outward.
This energy heats the outer layer and causes expansion
Results in giant body size of star 100 to 1000 X size of it’s original main-sequence size

24. Death and Burnout of Stars
All stars run out of fuel and collapse because of gravity

25. Death of Low Mass Stars Small Cool Red Consume hydrogen fuel slowly
Not hot enough to fuse helium
Remain on the main sequence for up to 100 billion years
Collapse into White Dwarfs

26. Death of Medium Mass Stars
Masses similar to our Sun
Evolve into Giants
consume hydrogen and helium at fast rate
Collapse into White Dwarfs
During collapse from Red Giant into White Dwarf they cast off their outer shell and leave a cloud of gas called planetary nebulae

27. Death of Massive Stars Massive stars have short lives
End star life in brilliant explosions called supernova
Rare
Death is triggered when nuclear fuel is consumed
Star collapses
Implodes
Sends shock wave out from the stars interior, this destroys the star blasting the shell into space
None have been observed since the invention of the telescope

28. Nucleosynthesis – the process that produces chemical elements inside stars
Occurs in dying stars
Stars produce all naturally occurring elements beyond helium in the periodic table
Mass of the star determines the highest atomic number of the elements it can produce
More massive stars produce heavier elements

29. Study of Light
Information about the universe is obtained from the study of the light emitted from stars and other bodies in space

30. Electromagnetic Radiation
Gamma Rays
X-Rays
Ultraviolet Rays
Visible Light
Infrared Radiation
Microwaves
Radio waves
All energy travels through the vacuum of space at the speed of light

31. Electromagnetic Spectrum – arrangement of waves according to their wavelengths and frequencies
Photons – a stream of particles

32. When the spectrum of a star is studied, the spectral lines act as “fingerprints”. Spectral lines identify the elements present in a star and tell of the stars chemical composition