1. Chapter 2
Stars and Galaxies

2. Where are you? The Earth circles the sun
The sun is one of billions of billions of stars.
To measure distances between stars we a distance measurement called the Light- year
1 light-year is the distance light travels in one year.

3. Light-Year Light moves at 300,000 km/sec That’s 186,000 mile/sec
It would reach the sun in about 5 minutes
How far would it go in a year?
Nearest star is 4.3 light years away

4. Binary Stars Most stars are found in pairs
These stars revolve around each other
If a dim star passes in front of a bright star, it will block its light.
Called an eclipsing binary
Algol dims every 69 hours
The closest star -Alpha Centari is actually a triple star system

5. Binary System
Side
Top

6. Constellations Groups of stars that appear to stay together Zodiac
Named after gods, animals, and heroes
Stars are not necessarily near each other

7. Nova A star getting suddenly brighter Occurs in a binary star system
Gases from one star are pulled into the other.
Causing a nuclear explosion.

8. Clusters Smaller groups of stars within a galaxy
Globular Clusters- Spherical shaped with may (up to 100,000 stars)
Open clusters- less organized- with fewer stars ( hundreds )

9. Nebula Gas and dust clouds in space. Most can’t be seen
If they reflect light from nearby stars they can be seen
Probably the birthplace of new stars

12. Ring Nebula

14. Galaxies Huge collections of stars
each may contain hundreds of billions of stars
The major feature of the universe
Maybe as many as 100 billion galaxies

15. Types of Galaxies
Elliptical - round, from flat disks to spheres - contain older stars
Spiral- Flattened arms that spin around a center
Irregular- no definite shape -less common

16. Andromeda

17. Large Magellanic Cloud

18. M51

19. M83

20. Milky Way Our galaxy almost all the stars you can see in the sky
100,000 light-years across
15,000 top to bottom
100 to 200 billion stars

21. Spectrum

22. Prism
White light is made up of all the colors of the visible spectrum.
Passing it through a prism separate it.

23. If the light is not white
Stars give off different colors of light
Passing this light through a prism does something different.
How we know what stars are made of.

24. Spectra from stars will have lines missing

25. Doppler Effect
Change in wavelength caused by the apparent motion of the source.
Cars moving by you
Same things happen to light
Light from objects coming toward you is compressed looks more blue
Light from objects away looks more red

26. Red Shift
Light from galaxies moving away

27. Blue Shift
Light from galaxies moving toward us

28. A big surprise No Galaxies showed blue shift
All galaxies showed red shift.
Which means
All galaxies were moving away
The universe is expanding

29. The Big Bang Theory
The universe started with a concentrated area of matter and energy.
15-20 billion years ago
Then it exploded and has been expanding ever since
Faster moving stuff traveled farther
Explained red shift

30. Big Bang Theory Predicts energy should be evenly distributed
Astronomers did find it
Called background radiation
Evenly spread throughout the universe.

31. Gravity Force of attraction All objects attract each other.
Pulled matter into clumps
These clumps became bigger
became galaxies

32. Open or closed? Two possible results of big bang.
Open universe will continue expanding
Stars will eventually lose all energy
end of universe is emptiness.
In a few hundred billion years

33. Closed Universe
Gravity will eventually pull all the galaxies back together.
Eventually all matter will come back together at the center of the galaxy
Blue shift
Packed into a area as small as a period.
Then another big bang
Every 80 to 100 million years.

34. Quasars Quasi - stellar radio source Quasi- means “something like”
stellar means “star”
Most distant objects in the universe -12 billion light years
Give off tremendous energy as x-rays and radio waves
as much as 100 galaxies

35. Quasars 1 sec, enough for 1 billion years electricity for Earth
At the edge of the universe
At the very beginning of the universe

36. Another Tool Spectroscope
Breaks the light of a star up into its colors
Called a spectrum
Kind of spectrum tells scientists
what the star is made of
which way and how fast it is moving

37. Stars Are formed by the same forces Have different Size Composition
Temperature
Color
Mass
Brightness

38. Size 5 main categories Medium sized - like our sun
from 1/10 size of sun to 10 times it’s size
Giant stars- 10 to 100 times bigger than the sun
Supergiant stars- 100 to 1000 times bigger than the sun

39. Size White dwarfs- smaller than 1/10 the size of the sun
Neutron stars - smallest stars - about 16 km in diameter

40. Composition Determined with a spectroscope
by the colors of light it gives off
The lightest element Hydrogen makes up % of a star
Helium is second most
96-99 % is hydrogen and helium
rest is other elements -

41. Temperature Color also indicates temperature hottest surface 50000 °C
coolest -3000°C
Blue
White
Yellow
Red-orange
Red
35,000 °C
10,000 °C
6,000 °C
5,000 °C
3,000 °C

42. Brightness Magnitude - measure of brightness
Apparent magnitude - how bright it looks from earth
Absolute magnitude - how bright it really is
Variable stars - brightness changes from time to time
Cephid variables - pulsating variables- change both brightness and size

43. Hertzsprung-Russell diagram
Found that as temperature increased, so did absolute magnitude
90% of stars followed this pattern
Called main sequence stars
Other 10% were once main sequence stars but have changed over time

44. Supergiants Giants Main sequence Absolute Magnitude White Dwarfs 50000
20000
10000
6600
6000
5000
3000

45. Distance to stars One method is parallax
Apparent change in position as the earth goes around the sun

46. Measure the angle to the star
Wait half a year
Measure the angle to the star
Triangle tells distance

47. Distance to stars Parallax works only to 100 light-years
More than 100 light-years they use a complicated formula based on apparent and absolute magnitude.
More than 7 million light-years they use the red shift

48. Why Stars Shine Stars are powered by nuclear fusion
Hydrogen atoms join to form helium
Happens because gravity pulls the atoms in the core so close together
The sun turns 600 billion kilograms of hydrogen to kilograms of helium every second
The 4.2 billion kilograms of mass are turned to energy -light, heat, UV, x-rays
E= mc2

49. The Sun An average star Over 1 million earth’s would fit inside
1/4 the density of the Earth
made of 4 layers

50. Corona- Outermost layer
Temp-1,700,000ºC
Few particles
Chromosphere-
middle of atmosphere
Temp-27,800ºC
1000’s of km thick

51. Corona

52. Chromosphere

53. Photosphere-
Temp-6000ºC
550 km thick
Surface of the sun
Core-
1,000,000ºC
15,000,000ºC

54. Activity on the Sun Storms on the sun
Prominences- Loops or arches of gas that rise from the chromosphere
Solar Flares- Bright bursts of light, huge amounts of energy released
Sunspots- Dark areas on the suns surface
in the lower atmosphere
Motion shows the rotation of the sun
Interferes with radio

55. Solar Prominence

56. Solar Wind Continuous stream of high energy particles.
Can also interfere with radio and TV

57. Star Life Cycles Stars change over time New stars form from nebulae
Gravity pulls the dust and gas together
Mostly hydrogen
Forms a spinning cloud
Hydrogen atoms hit each other and heat up

58. Star Life Cycle
When the temperature reaches 15,000,000 °C fusion begins
Makes a protostar - a new star
What determines the life cycle of the star is how much mass it starts with.

59. Medium-Sized stars
Shine for a few billion years as hydrogen turns to helium.
When hydrogen is used up, the core is almost all helium.
Helium core shrinks and heats up
Makes outside expand and cool
Gives off red light
Becomes red giant

60. Medium-Sized Stars Helium in core turns to carbon
Last of hydrogen gas drifts away to become a ring nebula or a planetary nebula.
When last of helium is used up the core collapses and becomes a white dwarf
Incredibly dense- a teaspoon will weigh tons

61. How long It depends on the mass.
The smaller a star starts out, the longer it takes
From a few to 100 billion years for medium sized stars
The sun will take about 10 billion years

62. Massive Stars Start with at least 6 times the mass of the sun.
Like medium stars up until they become red giants.
The helium in the core becomes carbon, but it keeps getting hotter.
Carbon atoms for heavier elements like oxygen and nitrogen and even iron

63. Massive stars Then heavier atoms can form
Can’t go further than iron.
Iron absorbs energy until it explodes in a supernova
Temperatures up to 100,000,000,000°C
Then heavier atoms can form
Explosion results in a new nebula,but with the new elements

64. Neutron Stars
If the star started out 6 to 30 times the mass of the sun, the core of the exploding star becomes a neutron star.
As massive as the sun, but only 16 km across.
Neutron stars spin rapidly and give off pulses of radio waves
If these radio waves come in pulses it is called a pulsar

65. Black holes If the star was bigger than 30 times the mass of the sun
The left over core becomes so dense that light can’t escape its gravity.
Becomes a black hole.
Grab any nearby matter and get bigger
As matter falls in, it gives off x-rays.
That’s how they find them