1. AAIM:
DO NOW:
AHW:

2. AAIM: WHAT ARE STARS? DO NOW: 1. Take GALAXY HW
AHW: 1. LAB #18 CHARACTERISTICS OF STARS DUE TOMORROW
2. TEST MONDAY/TUESDAY NEXT WEEK (ASTRONOMY UNIT)
3. REVIEW DUE THURSDAY

6. The H.R. Diagram

8. STARS

9. What are Stars?
Large spheres of gas (Hydrogen and Helium)

10. Held together by gravity
Produce tremendous amounts of ENERGY

11. What fuels a star? The Sun is composed of 75% Hydrogen and 25% Helium
The process of Hydrogen fusing with Hydrogen to create Helium
This is called nuclear fusion
Young stars have more Hydrogen than Helium
The Sun is composed of 75% Hydrogen and 25% Helium

14. What is Luminosity?
Luminosity is the actual brightness of the stars compared with that of our sun
This is sometimes referred to as absolute magnitude

16. Life cycle
of Stars

17. Nebula
Stars are “born” from clouds of gas and dust originating from the Big Bang

19. What is a protostar?
A protostar is a swirling disk of matter in which gravity is pulling inward

20. Once fusion begins the protostar becomes a star
A star is born!
Once fusion begins the protostar becomes a star
Gravity and pressure work against each other and the star remains stable

21. AAIM: FINISH STARS
DO NOW: 1. TAKE OUT LAB # 18
AHW: REVIEW WILL BE COLLECTED THURSDAY

22. What determines the fate of stars?
A stars fate depends on its initial mass

23. Main-Sequence Stars 90% of all stars are Main-Sequence
How long they remain depends on their mass

25. Lower mass stars eventually become white dwarfs
Higher mass stars become Neutron stars or black holes

27. What is the fate of our Sun?
Main Sequence Star
Low mass
Eventually, our Sun will run out of “fuel” (Hydrogen)

28. With a lower temperature, the core of the Sun will expand
It will become a Red Giant, and swell to 100 – 1000 times bigger than it currently is

29. It will engulf the orbits of Mercury, Venus, and possibly even Earth

31. The Core of the Sun will expand & eventually engulf Earth

33. After becoming a red giant, it will shed its outer layers and shrink
This is called a planetary nebula

34. Finally, our Sun will become a White Dwarf
White Dwarfs are very small (only about the size of planet Earth)

35. They are dim (low luminosity)
They represent the last stage of the Sun’s energy (when all nuclear fuel has been used up)

36. Low- Mass stars become white dwarfs

37. The Evolution of our Sun

38. What about the big stars!
High mass stars will become SUPER giants
Eventually they will contract and explode
This is called a supernova

39. This star exploded 15,000 yrs. ago
Supernova Explosion
This star exploded 15,000 yrs. ago

40. Most become neutron stars after exploding
Others……become………..BLACK HOLES!!!!!!

41. Black Holes
Black holes form when extremely massive stars collapse

42. Cygnus X-1 – Binary Star System
                                             
Black Hole

43. A Black Hole warps space time
Event Horizon
Singularity