1. STARS

2. A Nuclear Furnace 1. A star is like a gigantic nuclear furnace.
2. The nuclear reactions inside convert hydrogen into helium by means of a process known as fusion.
3. It is this nuclear reaction that gives a star its energy.

3. Classifying Stars
Scientists classify stars by:
Temperature
Brightness

4. Star Temperature
1. The color of a star tells us about its temperature.
Blue stars are the hottest, 7500°C- 30,000°C.
Red stars are the coolest, less than 3500°C.
Our sun is yellow in color, in the middle of the temperature scale, from 5000°C-7500°C.

5. Betelgeuse-
Red Star- Coolest
Rigel-
Blue Star-Hottest
CONSTELLATION ORION

6. Brightness or Magnitude
1. Stars are also classified by their brightness.
2. The brightness of a star as seen from Earth is called apparent magnitude.
3. The actual brightness of a star is called absolute magnitude.
Example: The SUN has an absolute magnitude of 4.8 when compared to the other stars. The SUN has an apparent magnitude of because it is so close. The lower the number the brighter the star.

7. Another Example of absolute and apparent magnitude.
Which light is brighter, A or B?

8. Light A is brighter than light B.
We see the apparent magnitude of the lights (how they look to us)
If lights A and B were next to each other they would look the same because the two lights are exactly the same.
Their absolute magnitude is the same.
Distance makes them look different. The same is true for stars.
Two stars could be the same brightness but their distance from us makes their brightness different.

9. H-R Diagram
Brighter
1. The H-R Diagram shows us color, size, temperature, absolute magnitude and the life cycle of stars.
Dimmer
Hotter Cooler

10. Life Cycle of A Star
1. Stars begin their lives as clouds of dust and gas called a stellar nebula.

11. A Protostar
The gravity of a passing star or the shock wave from a nearby supernova may cause the nebula to contract.
1. Matter in the gas cloud will begin to come together into a dense region called a protostar.
2. As the protostar continues to condense, it heats up.
3. Eventually, it reaches a critical mass and nuclear fusion begins.
4. This begins the main sequence phase of the star. Our Sun is a main sequence star.

12. PROTOSTAR

13. Main Sequence Stars 1. The life span of a star depends on its size.
2. Very massive stars will become blue giants during their main sequence.
Their main sequence may last only a few hundred thousand years.
3. Smaller stars, like the Sun, will burn for several billion years during their main sequence stage.
4. Our Sun is in its main sequence.

14. Average sized star like our Sun during main sequence.
The main sequence is the longest part of a star’s life
Average sized star like our Sun during main sequence.
Massive star larger than our Sun during main sequence

15. Red Giant and Red Supergiant
1. Eventually, the star's fuel will begin to run out.
2. Our Sun will expand into what is known as a red giant.
3. Massive stars will become red supergiants.
4. This phase will last until the star exhausts its remaining fuel.
5. At this point, the star will collapse.

17. Our Sun
1. Most average stars will blow away their outer atmospheres to form a planetary nebula.
2. Their cores will remain behind and burn as a white dwarf until they cool down.
3. What will be left is a dark ball of matter known as a black dwarf.

18. Planetary Nebula

19. White Dwarf

20. Massive Stars
1. If the star is massive enough, the collapse will trigger a violent explosion known as a supernova.
2. If the remaining mass of the star is about 1.4 times that of our Sun, it will collapse further to become a neutron star.
3. If the remaining mass of the star is more than about three times that of the Sun, it will collapse and what is left behind is an intense region of gravity called a black hole.

21. Massive Stars (Larger than our Sun)
Become Red Supergiants.

22. Red Supergiant becomes Supernova in a giant explosion,

23. OR It becomes a Black Hole
This is an illustration, not an actual black hole!!

24. Supernova Becomes a Neutron Star

25. Life Cycle of our Sun Stellar Nebula Protostar Main Sequence Red Giant
Planetary Nebula
White Dwarf
Black Dwarf

26. Life Cycle of a Massive Star
Stellar Nebula
Protostar
Blue Giant
Red Supergiant
Supernova
Neutron Star
(Pulsar) OR
7. Black Hole

27. Interactive Website