2. Which star color indicates the hottest star surface temperature?
(1) blue (3) yellow
(2) white (4) red

4. Of stars and expanding universes…

5. The universe is big and it is expanding!
We know this by studying starlight.
Starlight informs us of many things in space, such as an objects: age, composition, distance, & more.
Let’s study stars and their light…

6. Dust--in a nebula--is
pulled together by gravity.
When the mass and heat
reach a critical point, fusion
of hydrogen begins .
The star is “born” and begins to emit light (radiation).

8. Which process produces the energy that allows the stars of the universe to radiate visible light?
(1) convection
(2) Insolation
(3) nuclear fusion
(4) radioactive decay

9. Stars live in a “tug-of-war” between fusion energy pushing out and gravity pulling in.
Eventually the hydrogen fuel runs out and the size of the star determines its final destiny.

10. Our sun is an average star
Our sun is an average star. When it runs out of hydrogen fuel to fuse, what will be its fate?

12. What is the temperature of a “main sequence” star with a luminosity of about 50?
Which star has about the same temperature as the sun,
but is about 5000 times brighter (more luminous)?

13. Remember starlight informs us of :
The age of the universe (13.73 bya).
That the universe is expanding.
But let’s save this and more for another day…

15. Which star color indicates an 8000K main sequence star?
(1) blue (3) yellow
(2) white (4) red

17. Which type of electromagnetic energy has the longest wavelength?
(1) infrared radiation
(2) radio wave radiation
(3) ultraviolet radiation
(4) x-ray radiation

19. How does starlight inform us that the universe is expanding?

20. HEY…THIS IS NO
MONKEY
BUSINESS!!!!

21. Light is fast!

22. Light takes seconds

23. Light takes about
1.5 seconds

24. Light takes
about 8.5
minutes

25. Light takes about
100,000 years!

26. Light from across the universe may take billions of years to reach us.
That means we are looking billions of years into the past!

27. Energy is transferred from the Sun to Earth mainly by
(1) molecular collisions
(2) density currents
(3) electromagnetic waves
(4) red shifts

29. Light from stars travels in many colors.

30. It does not ALWAYS arrive in the color we expect though!

31. Light waves spread out in all directions from a star, like waves in the water if you throw a rock.

32. This is called Red Shifting.
The waves of light get longer (they “stretch out”) if the object is moving away very quickly.
This is called Red Shifting.
(because the colors “shift” toward red)

33. BTW…if the object is coming at you quickly the waves blue shift (they squeeze together)!

34. Red Shift
blue Shift

35. Distant objects are moving away quickly.
Their light waves “stretch out” and get longer…becoming more red.

36. THE
UNIVERSE IS
EXPANDING!

38. This is evidence that these galaxies are
When viewed from Earth, the light from very distant galaxies shows a red shift.
This is evidence that these galaxies are
(1) revolving around the Sun
(2) revolving around the Milky Way
(3) moving away from Earth
(4) moving toward Earth

45. Astronomers viewing light from distant galaxies observe a shift of spectral lines toward the red end of the visible spectrum. This shift provides evidence that
(1) orbital velocities of stars are decreasing
(2) Earth’s atmosphere is warming
(3) the Sun is cooling
(4) the universe is expanding

46. What happens next depends upon the size of the star.
The “tug of war” between gravity and fusion will end when the star runs out of Hydrogen fuel.
Gravity
Fusion
What happens next depends upon the size of the star.

47. What about the light?
Good question!