Star Light, Star Bright

1. Star Light, Star Bright

2. 3 Factors that determine the brightness of a star Temperature Hotter the star the brighter the star Blue…..white……..yellow…….orange…….….red HOTTEST----------------------------------------------COOLEST

3. Size • Larger the star Brighter the Star • Smaller the star Dimmer the Star

4. Distance • Closer the star Brighter the star • Further the star Dimmer the star

5. Brightness Key Terms • Luminosity • Apparent Magnitude • Absolute Magnitude • Parallax

6. Luminosity • Definition- actual or true brightness of a star • Total amount of energy given off • Dependent on 2 things: Temperature Size 6000K 6000K 6000K 10,000K More luminous More luminous

7. Apparent Magnitude • Definition- how bright a star appears when seen from earth • System developed where a number is assigned to a star based on brightness • Smaller # Brighter the star Bigger # Dimmer the star • Sun -28 , Full Moon -11, Polaris 7 • Hubble can see +28

8. Absolute Magnitude • Definition- brightness of a star as if all stars were seen from the same distance Earth Earth Sun- average star, Abs. Mag of +4.8 (less luminous, looks brighter because closer) Rigel- orion, Abs, Mag. of -6.4 (more luminous, further away) To Determine: apparent magnitude and distance to earth

9. Moving Stars? • Parallax- the apparent change in position of a star due to the movement of observer Finger: left/right

10. Life Cycle of a Star

11. Life Cycle of Stars Planetary Nebula White Dwarf Red giant 1 Main Sequence Star Nebula Protostar Red supergiant 2 Supernova Black Hole Neutron Star

12. Life Cycle Introduction • http://www.youtube.com/watch?v=f_KLOFe2rDY • http://www.youtube.com/watch?v=YU6X3SPZAJo

13. Stars are born in nebulae (huge clouds of gas and dust) Nebula begin to condense when an outside force, such as shock wave, acts upon it Step 1: Initiation

14. Step 2: Pre-star • A protostar forms when a part of the nebula contracts, shrinks, and pressure and internal temperature increases • Protostar begins to glow where nebula is contracting

15. As contraction, temperature, density, and pressure increase protostar gets larger and brighter Center becomes so hot fusion begins Once fusion begins, a star is born TRUE STAR Step 2 contd: A star is born

16. Internal temperature hot enough to start fusion at center said to be a main sequence star Sun is an example Each protostar will turn into one main sequence star 90% of stars are main sequence stars Vary in surface temperature and absolute magnitude Step 3: Teenager star

17. Fate determined by Size • If a normal size star (Sun) follows path 1 • If star is a GIANT follows path 2

18. Path 1

19. Red giant- very bright, once an average star, but is now close to end of life Has expanded to many times its original size (heat causes it to expand) Hydrogen core has turned to helium and eventually to carbon Our sun will become a red giant star in about 5 billion years Step 4: Middle-aged star

20. Star begins to die when its core temperature rises to a point where fuel is used up A carbon-oxygen core forms Eventually the gases at a star’s surface begin to blow away in abrupt bursts Resulting glowing halo is called a planetary nebula Star like our sun begins to die

21. atoms no longer fuse, fuel is used up Outer gases escape leaving the core which collapses and shrinks Heat still present but will continue to escape for about a billion of years White Dwarf- small, very dense, hot star at the end of its life, mostly carbon with nuclear cores depleted (about the size of earth but heavier) Death of a star like our sun

22. Path 2

23. Supergiant- largest known type of star can be as large as our solar system rare but exists In a massive star, hydrogen is fused more quickly and fusion continues until a iron nuclei is formed Step 4: Middle-aged massive star

24. Elements are used up very quickly and eventually runs out of fuel Collapse of the core produces a shock wave that blasts the star’s outer layers into space producing a supernova Supernova- exploding star Death of a Supergiant

25. After a massive star “goes supernova” it leaves behind its core (called a neutron star) -Neutron Star- small, dense star made of neutrons When neutron star is first formed, it spins very rapidly and gives off radio waves Option A after a supernova

26. Black Hole- a star that collapses How do we know they exist? Pulls gases off nearby stars, as gas is pulled into this “nothing space” x-rays are emitted from the gas as molecules are pulled in Option B after a supernova

27. Cycle continues • Star is born from great clouds of gas and dust • Stars mature, grow old, and die • As a star dies, it makes new clouds of dust gas and dust where new stars can begin to form • More massive a star, the shorter its life

28. http://www.youtube.com/watch?v=HfqcZdNnQ6s

29. Hertzsprung-Russell Diagram • Graph that compares temperature and absolute magnitude (brightness)

30. The Hertzsprung-Russell Diagram (H-R diagram) Cool and bright Bright Hot and bright Cool and dim Hot and dim Sun Dim Hot Cool

31. Supergiants Hot and bright Cool and bright Giants Main sequence White Dwarfs Cool and dim Hot and dim