1. The Earth and the Universe
Beyond our Solar System

2. Properties of stars Distance
Measuring a star's distance can be very difficult
Stellar parallax
Used for measuring distance to a star
Apparent shift in a star's position due to the orbital motion of Earth
Measured as an angle

3. Parallax is larger for closer objects
Image from:

4. Properties of stars Distance Units of measurement
Kilometers or astronomical units are too cumbersome to use
Light-year is used most often
Distance that light travels in 1 year
One light-year is 9.5 trillion km (5.8 trillion miles)

5. Properties of stars Stellar brightness Controlled by three factors
Size
Temperature
Distance

6. Properties of stars Stellar brightness
Magnitude - Measure of a star's brightness
Two types of measurement
Apparent magnitude
Brightness when a star is viewed from Earth
Decreases with distance
Numbers are used to designate magnitudes - dim stars have large numbers and negative numbers are also used

7. Properties of stars Stellar brightness
Magnitude - Measure of a star's brightness
Two types of measurement
Absolute magnitude
"True" or intrinsic brightness of a star
Brightness at a standard distance of 32.6 light-years
Most stars' absolute magnitudes are between -5 and +15

9. Properties of stars Color and temperature Hot star
Temperature above 30,000 K
Emits short-wavelength light
Appears blue
0°C = 273 K

10. Properties of stars Color and temperature Cool star
Temperature less than 3000 K
Emits longer-wavelength light
Appears red

11. Properties of stars Color and temperature Between 5000 and 6000 K
Stars appear yellow
e.g., Sun

12. Properties of stars Binary stars and stellar mass Binary stars
Two stars orbiting one another
Stars are held together by mutual gravitation
Both orbit around a common center of mass
More than 50% of the stars in the universe are binary stars

13. Binary stars orbit each other around their common center of mass

14. Properties of stars Binary stars and stellar mass Stellar mass
Determined using binary stars – the center of mass is closest to the most massive star
Mass of most stars is between one-tenth and fifty times the mass of the Sun

15. Hertzsprung-Russell diagram
Shows the relation between stellar
Brightness (absolute magnitude) and Temperature
Diagram is made by plotting (graphing) each star's
Luminosity (brightness) and Temperature

17. Variable stars Stars that fluctuate in brightness
Types of variable stars
Pulsating variables
Fluctuate regularly in brightness
Expand and contract in size
Eruptive variables
Explosive event
Sudden brightening
Called a nova

18. Interstellar matter Between the stars is "the vacuum of space" Nebula
Cloud of dust and gases
Two major types of nebulae
Bright nebula
Glows if it close to a very hot star
Two types of bright nebulae
Emission nebula
Reflection nebula

19. The Orion Nebula is a well-known emission nebula

20. A faint blue reflection nebula in the Pleiades star cluster

21. Interstellar matter Nebula Two major types of nebulae Dark nebula
Not close to any bright star
Appear dark
Contains the material that forms stars and planets

22. Stellar evolution Stars exist because of gravity
Two opposing forces in a star are
Gravity – contracts
Thermal nuclear energy – expands

23. Stellar evolution Stages Birth In dark, cool, interstellar clouds
Gravity contracts the cloud
Temperature rises
Radiates long-wavelength (red) light
Becomes a protostar

24. Stellar evolution Stages Protostar
Gravitational contraction of gaseous cloud continues
Core reaches 10 million K
Hydrogen nuclei fuse
Become helium nuclei
Process is called hydrogen burning
Energy is released
Outward pressure increases
Outward pressure balanced by gravity pulling in
Star becomes a stable main-sequence star

25. Stellar evolution Stages Main-sequence stage
Stars age at different rates
Massive stars use fuel faster and exist for only a few million year
Small stars use fuel slowly and exist for perhaps hundreds of billions of years
90% of a star's life is in the main-sequence

26. Stellar evolution Stages Red giant stage
Hydrogen burning migrates outward
Star's outer envelope expands
Surface cools
Surface becomes red
Core is collapsing as helium is converted to carbon
Eventually all nuclear fuel is used
Gravity squeezes the star

27. Stellar evolution Stages Burnout and death Final stage depends on mass
Possibilities:

29. H-R diagram showing stellar evolution

30. Stellar remnants White dwarf Small (some no larger than Earth) Dense
Can be more massive than the Sun
Spoonful weighs several tons
Atoms take up less space
Electrons displaced inward
Called degenerate matter
Hot surface
Cools to become a black dwarf

31. Stellar remnants Neutron star Forms from a more massive star
Star has more gravity
Squeezes itself smaller
Remnant of a supernova
Gravitational force collapses atoms
Electrons combine with protons to produce neutrons
Small size

32. Stellar remnants Neutron star Pea size sample Strong magnetic field
Weighs 100 million tons
Same density as an atomic nucleus
Strong magnetic field
First one discovered in early 1970s
Pulsar (pulsating radio source)
Found in the Crab nebula (remnant of an A.D supernova)

33. Crab Nebula in the constellation Taurus

34. Stellar remnants Black hole More dense than a neutron star
Intense surface gravity lets no light escape
As matter is pulled into it
Becomes very hot
Emits x-rays
Likely candidate is Cygnus X-1, a strong x-ray source

35. Galaxies Milky Way galaxy Structure
Determined by using radio telescopes
Large spiral galaxy
About 100,000 light-years wide
Thickness at the galactic nucleus is about 10,000 light-years
Three spiral arms of stars
Sun is 30,000 light-years from the center

36. Face-on view of the Milk Way Galaxy

37. Edge-on view of the Milk Way Galaxy

38. Galaxies Milky Way galaxy Rotation Around the galactic nucleus
Outermost stars move the slowest
Sun rotates around the galactic nucleus once about every 200 million years

39. Galaxies Milky Way galaxy Halo surrounds the galactic disk Spherical
Very tenuous gas
Numerous globular clusters

40. Galaxies Other galaxies
Existence was first proposed in mid-1700s by Immanuel Kant
Four basic types of galaxies
Spiral galaxy
Arms extending from nucleus
About 30% of all galaxies
Large diameter of 20,000 to 125,000 light years
Contains both young and old stars
e.g., Milky Way

41. Great Galaxy, a spiral galaxy, in the constellation Andromeda

42. Galaxies Other galaxies Four basic types of galaxies
Barred spiral galaxy
Stars arranged in the shape of a bar
Generally quite large
About 10% of all galaxies

43. A barred spiral galaxy

44. Galaxies Other galaxies Four basic types of galaxies Elliptical galaxy
Ellipsoidal shape
About 60% of all galaxies
Most are smaller than spiral galaxies; however, they are also the largest known galaxies

45. Galaxies Other galaxies Four basic types of galaxies Irregular galaxy
Lacks symmetry
About 10% of all galaxies
Contains mostly young stars
e.g., Magellanic Clouds

46. Galaxies Galactic cluster Group of galaxies
Some contain thousands of galaxies
Local Group
Our own group of galaxies
Contains at least 28 galaxies
Supercluster
Huge swarm of galaxies
May be the largest entity in the universe

47. Red shifts Doppler effect
Change in the wavelength of light emitted by an object due to its motion
Movement away stretches the wavelength
Longer wavelength
Light appears redder
Movement toward “squeezes” the wavelength
Shorter wavelength
Light shifted toward the blue

48. Red shifts Doppler effect
Amount of the Doppler shift indicates the rate of movement
Large Doppler shift indicates a high velocity
Small Doppler shift indicates a lower velocity

49. Raisin bread analogy of an expanding universe

50. Red shifts Expanding universe
Most galaxies exhibit a red Doppler shift
Far galaxies
Exhibit the greatest shift
Greater velocity
Discovered in 1929 by Edwin Hubble
Hubble's Law – the recessional speed of galaxies is proportional to their distance
Accounts for red shifts

51. Big Bang theory Accounts for galaxies moving away from us
Universe was once confined to a "ball" that was
Supermassive
Dense
Hot

52. Big Bang theory Big Bang marks the inception of the universe
Occurred about 15 billion years ago
All matter and space was created
Matter is moving outward
Fate of the universe
Two possibilities
Universe will last forever
Outward expansion sill stop and gravitational; contraction will follow

53. Big Bang theory Fate of the universe
Final fate depends on the average density of the universe
If the density is more than the critical density, then the universe would contract
Current estimates point to less then the critical density and predict an ever-expanding, or open, universe