1. Types of Stars Life Cycle of Stars Galaxies
Astronomy
Types of Stars
Life Cycle of Stars
Galaxies

2. Characteristics of Stars
Color
Gas Composition
Temperature
Magnitude

3. Color/ Temperature
A star’s surface temperature can be determined by their color
Blue stars have a temperature above 30,000 K
Red stars are much cooler
Yellow stars have temperatures between 5000 and 6000 K (such as our Sun)

4. Binary Stars Binary Stars Pair of stars that orbit around each other
Stars are kept together by gravity
More than half of all stars are binary or clusters

5. Binary Stars: Sirius and its Tiny Companion

6. Taken from Hubble Space Telescope
Star Cluster
Taken from Hubble Space Telescope

7. Star Distance Measurement
A light-year is the best unit to express stellar distance.
It is the distance light travels in one year.
Example: A star that is 4.3 light-years away means that it takes 4.3 years for light from that star to reach our Sun.

8. Magnitude This is how bright the star is (or appears to be)
It can appear brighter if…
The star is really close to Earth
Actual brightness usually depends on size

9. Hertzsprung–Russell Diagram
Makes no sense without caption in book

10. Hertzsprung-Russell Diagram
Shows relationship between a star’s magnitude and temperature
Main-Sequence line–
as magnitude increases, so does temperature
Notice how stars are colored blue, red, and yellow!!!

11. Hertzsprung–Russell Diagram
Makes no sense without caption in book

12. H-R Diagram Almost 90% of all stars belong on the main-sequence
The brighter stars are the hottest (blue)
50 times more massive than Sun

13. H-R Diagram Continued
In the upper right corner of diagram are the red giants
Large red giants are called supergiants (Betelgeuse in constellation Orion)
In the lower-central part of diagram are the white dwarfs

14. Hertzsprung–Russell Diagram
Makes no sense without caption in book

15. Where it all starts…
Cloud of Gas and Dust

16. Birth of a Star Clouds of dust and gas in space
92% Hydrogen and 7% Helium
All stars must have started with these gases.
These clouds are also known as “nebula”

17. The Famous Eagle Nebula
First taken by the Hubble Space Telescope in 1995

18. Orion Nebula

19. Gravity is important!!
Gravity squeezes particles into the center of the cloud of dust and gas
Without gravity, stars would not develop!!

20. Balanced Forces
Makes no sense without caption in book

21. Nuclear Fusion A star is born once nuclear fusion has begun
Nuclear fusion is the process of combining atoms to create tremendous amounts of energy.
The first atoms to combine are hydrogen. They combine to create helium.

22. Main-Sequence Stage
Stars age at different rates while in the main-sequence
Hot, massive blue stars burn their hydrogen really fast
Yellow stars (our sun) are in this stage for 10 billion years
Remember: Our sun is only 5 billion years old…. So it still has 5 billion years left just in this stage!!

23. Yellow Star- Our Sun

24. Red-Giant Stage Star expands
100’s to 1000’s size of main-sequence star
Convert helium to carbon to produce fuel and delay death
Eventually all usable elements will be burned
Yellow stars (sun) usually spend less than a billion years as a red giant

25. Burnout and Death A star’s life cycle depends on the star’s mass.
Medium Mass Stars and Massive Stars will evolve and die differently

26. Medium-Mass Stellar Death
Medium-Mass Stars (our sun)
Become red giants
During collapse as red giant, create a round cloud of gas known as a “planetary nebula”
End as white dwarfs
The leftover centers of the star

27. Taken from Hubble Space Telescope
Planetary Nebula
Makes no sense without caption in book
Taken from Hubble Space Telescope

28. Taken from Hubble Space Telescope
Planetary Nebula
Taken from Hubble Space Telescope

29. High-Mass Stellar Death
High-Mass Star
Red Giant implodes and creates a supernova
The gravity becomes too strong for the star to withstand
Extremely rare
The last supernova to be seen with the naked eye was in 1987.
The explosion actually began before civilization began here on Earth, but it took 169,000 years for the light from the explosion to reach Earth.

30. Crab Nebula in the Constellation Taurus
Makes no sense without caption in book
Taken from Hubble Space Telescope

31. Taken from Hubble Space Telescope
Supernova
Taken from Hubble Space Telescope

32. Taken from Hubble Space Telescope
Supernova Remnant
Taken from Hubble Space Telescope

33. Star Remnants Black Holes Remnants of supernova event
These remnants are so massive that they collapse
Gravity is so strong that light can not escape
Black holes do not “swallow up” other stars
However, some of the gas and dust from the star may spiral into the black hole.
Black holes were first “seen” by x-ray waves.

34. Black Hole
Artists’ Drawing

35. Black Hole
Makes no sense without caption in book

36. Review Medium-Mass Stars Massive Stars Cloud of gas and dust
Main-Sequence
Red Giant
Planetary Nebula
White Dwarf
Massive Stars
Cloud of gas and dust
Main-Sequence
Supergiant
Supernova
Blackhole

37. Galaxies
A galaxy is a group of stars, dust, and gases held together by gravity
The smallest galaxies still contain a few million stars.
Galaxies were first classified by Edwin Hubble in the 1920’s
Three types of galaxies
Spiral
Elliptical
Irregular

38. Types of Galaxies Spiral Disk-shaped with arms extending from center
30% of galaxies are spiral
Our galaxy, the Milky Way Galaxy
The outer edges of the spiral are blue because most of the blue stars in this galaxy are located on the spiral’s “arms”
The yellow and red stars are located in the middle

39. Spiral Galaxy

40. Spiral Galaxy

41. Milky Way Galaxy Earth’s galaxy Large spiral galaxy
100,000 light-years wide and 10,000 light-years thick

42. Structure of the Milky Way
Makes no sense without caption in book

43. Galaxies Continued Elliptical Range in shape- round to oval
60% of all galaxies are elliptical
These have very bright centers

44. Elliptical Galaxy

45. Elliptical Galaxy

46. Galaxies Continued Irregular No uniform shape
10% of galaxies are irregular
Our nearest galaxy

47. Irregular Galaxy
Makes no sense without caption in book

48. Irregular Galaxy

49. The Big Bang Theory Theory about the origin of the universe
At one time, the entire universe was confined to a dense, hot, supermassive ball. (To the size of a tennis ball!)
Then, about 13.7 billion years ago, a violent explosion occurred, hurling energy in all directions
Some of the expanding energy turned into matter
Matter made nebulas, which then made stars. Stars eventually made galaxies.

50. The Big
Bang
Theory
Makes no sense without caption in book

51. Supporting Evidence
In 1964, Robert Wilson and Arno Penzias, using a giant radio wave antenna, found radiation that was coming to Earth from all directions in space
Called “Cosmic Background Radiation”
This radiation was actually created from the Big Bang.

52. Future for the Universe?
Two possible futures:
The Universe will expand forever (most popular)
The outward expansion will stop and inward contraction will begin
These are just theories--- no one is certain how the Universe began and if it will end.