1. Stars, Galaxies and the Universe
Chapter 21
Stars, Galaxies and the Universe

3. Patterns of Stars are called CONSTELLATIONS.
Many sailors and different cultures have used the stars to guide them while traveling.
Slaves before the Civil War used the stars to escape to the North.
Patterns of Stars are called CONSTELLATIONS.

6. Electromagnetic Spectrum
We see visible light which is only a small part of the electromagnetic spectrum.
Light is a form of electromagnetic radiation, or energy that can travel through space in waves.

8. The longest wavelength is the radio wave.
The wavelength of radio waves can be as the size of a mountain.
The shortest wavelength is the gamma ray.
The wavelength of gamma waves can be the size of an atomic nucleus.

10. Infrared Radiation

12. The Sun Visible Light Ultra-violet radiation Infrared radiation
Radio emission
X-ray radiation

13. Waves What is the wavelength?
Visible light has very short wavelengths, less than one millionth of a meter.
Some electromagnetic waves are shorter and others can be several meters long.

15. ROY G. BIV
If you shine white light through a prism the light spreads out to make a range of different colors with different wavelengths, called a spectrum.
The electromagnetic spectrum includes:
Radio waves Infrared waves
Visible light Ultraviolet radiation
X rays Gamma rays

16. Telescopes
Telescopes collect and focus different types of electromagnetic radiation, including visible light.
The 2 types of telescopes we will discuss:
The Refracting Telescope
The Reflecting Telescope

17. Refracting Telescope
This telescope uses convex lenses to look at objects in the sky.
Convex lens is thicker in the middle than at the edges.
The larger the objective lens the more light the telescope can pick up making it easier to see faint objects.

19. Reflecting telescope
A reflecting telescope uses a mirror instead of an objective lens.
Like an objective lens the mirror focuses a lot of light onto a small area.
The larger the mirror the more light the telescope can collect.
The largest visible light telescopes are reflecting telescopes.

21. Spectrographs Most telescopes today have spectrographs.
A spectrograph breaks the light from an object into colors and photographs the resulting spectrum.
It can be used to determine:
The temperature of a star
The composition of a star

23. Bright Line Spectrum

24. Dark Line Spectrum

25. Characteristics of Stars
To travel to the nearest star at the speed of light it would take 4.2 years (Proxima Centauri).
Our sun and Proxima Centauri are only two stars that make up our Milky Way galaxy.
Our galaxy contains hundreds of billions of stars.
There are billions of galaxies in the Universe.

27. "The image, called the Hubble Deep Field (HDF), was assembled from 342 separate exposures taken with the Wide Field and Planetary Camera 2 (WFPC2) for ten consecutive days between December 18 and 28, 1995.
1,500 galaxies at various stages of evolution.
Most of the galaxies are so faint (nearly 30th magnitude or about four-billion times fainter than can be seen by the human eye) they have never before been seen by even the largest telescopes.

28. Leaving the Solar System, we move further out into the Universe and discover our greater place in space. The 2dF (2 degree field) survey shows the positions of over 100,000 nearby galaxies.

29. Our Galaxy is Huge
If you could travel at the speed of light it would take you 25,000 years to reach the center of our galaxy.
If you left our galaxy at the speed of light it would take you 2 million years to reach another galaxy.
A light-year is the speed light travels in one year which is approximately 9.5 million million kilometers.

31. Galactic Collision - Interacting galaxies NGC 2207 (left) and the smaller IC 2163, 114 million light-years away in the constellation Canis Major. Observations indicate that, billions of years from now, IC 2163 is destined to swing past the larger galaxy again and eventually merge into it.

32. Example
Dime = galaxy
Universe = 2 km

34. Measuring the Distance of Stars
It would seem impossible to measure objects so far away.
However astronomers have found a way.
Astronomers often use PARALLAX to measure the distances to nearby stars.

35. Everyday Parallax Example
A simpler example of parallax in the works is what you see every day when you look at a gauge such as the speedometer in your car or the hands of your watch. If you look straight over the needle, it will be exactly aligned with the number underneath. But if you look from the side, you might be unsure of where the needle is pointing.

36. PARALLAX
1. Hold your thumb at arms length in front of your face and look at it with one eye closed. Notice its placement with respect to the background.
2. Now close that eye and open the other one, and look at the background. Notice that your thumb seems to change position against the background -- it appears to move across the background.
This is because your eyes are a few centimeters apart from
each other and have a different point of view. This is what
gives you Stereo vision that lets you judge the distance of an
object. The angle the object appears to move from eye to eye
gives a measure of its distance.

37. Most stars are so far away that they never appear to move when viewed from the Earth. Astronomers use these far stars as a fixed background.
Repeat the thumb experiment, but move if closer to your face. Notice that the closer your thumb is to your eyes, the farther it appears to shift in the background. Even the nearest stars are so far away that astronomers can only measure a very small shift in the closest stars.

42. Classifying Stars
Like the sun all stars are huge spheres of glowing gas.
They are made of mostly hydrogen.
They make energy by nuclear fusion.

43. 4 Types of Stars: Red Giant, Supergiant Star, Giant Star
Main Sequence Star (Medium: Our Sun)
White Dwarf
Neutron Star

44. Our SUN

45. Types of Stars
Red Giants
White dwarfs

46. Our Sun It is not the biggest or the brightest star in the galaxy.
The reason it is so bright is because of how big it is.
When you look at stars in the sky they all appear to be roughly the same size.

47. Supergiants
Some stars are much larger than our sun and others are the size of Earth.
Astronomers use size along with temperature and brightness to classify stars.
Very large stars are called Giant Stars or Supergiants.
Example: Betelgeuse

48. Red Giants

49. Betelgeuse
If this star was our Sun it would extend all the way to Jupiter.

50. Eventually our Sun will start to run out of hydrogen
Eventually our Sun will start to run out of hydrogen. The core is now composed mostly of helium nuclei and electrons, and begins to collapse, driving up the core temperature, and increasing the rate at which the remaining hydrogen is consumed. The outer portions of the star expand and cool, producing the Red Giant phase.

52. White Dwarfs
White dwarf stars about the size of Earth.

53. Neutron Stars A neutron star are only 20 kilometers in diameter (12.4
miles),

54. Color A star’s color reveals it’s temperature.
Hot objects on Earth display the same range of colors.
Coolest Stars – about 3,200 degrees Celsius – reddish
Middle range stars – about 5,500 degrees Celsius – white
Hottest Stars – over 10,000 degrees Celsius – slightly bluer than the sun (IN CLASS EXAMPLE)

55. Brightness Of Stars Stars differ in brightness.
The brightness of a star depends on its size and temperature.
How bright a star is from Earth depends on:
How bright the star actually is
How far the star is from Earth

56. Brightness Brightness can be described in two different ways:
Apparent magnitude
Absolute magnitude
Apparent Brightness
This is how bright a star is seen from Earth.

57. Absolute Brightness Apparent Brightness
The brightness of a star if it were a standard distant away from the Earth.
Apparent Brightness
This is how bright a star is seen from Earth.

58. Hertzsprung-Russell Diagram (See Overhead)
These two gentlemen made graphs to determine if the temperature of stars and their brightness were related.
They plotted different stars onto the graph and noticed a pattern.
The graph they made is still used 100 years later and is called the Hertzsprung-Russell diagram or H-R diagram.
More than 90% of the stars are Main Sequence stars like our sun.

59. Stars

60. Stars Stars do not live forever.
Each star is born, goes through it’s life and dies.
Astronomers can not watch a star for a billion years to see all of the stages, but they look to see the difference between stars.
Stars

61. A Star is Born Stars are made of large amounts of gas in small space.
A nebula is a large amount of dust and gas over a large area. All stars start out as nebulas.
Gravity pulls some of the gas and dust in the cloud together.
The contracting cloud is then called a PROTOSTAR, meaning the earliest stage of a star’s life.
A star is born when the contracting gas and dust become so hot that nuclear fusion starts.

64. How long a star lives depends on how much mass it has.
Smaller stars last longer. Think of a small car, it has a small gas tank, but also burns gas slowly compared to a big car.
Small mass stars use up their fuel more slowly and live longer.

65. Stars less massive than our Sun can last for up to 200 billion years.
Our medium sized star (Sun) will last around 10 billion years.
Stars that is 15 times more massive than the Sun may last only 10 million years.

66. Death of Stars
When a star begins to run out of fuel, the center of the star shrinks and the outer part of the star expands.
The star will become a Red Giant or a Supergiant.
When a star runs out of fuel, it becomes a:
Black dwarf
Neutron star
Black hole

67. The Life of a Star

68. White Dwarf
Small mass and medium mass stars take 10 billion years or more to use up their nuclei fuel.
Then their outer layer expand and they become red giants.
Eventually the outer parts grow bigger and move out into space leaving the blue hot core of the star behind. This is called a white dwarf.

69. White Dwarf About the size of Earth
Same mass as our sun, but approximately one millionth the volume
Very dense (one spoonful of material from a white dwarf will have as much mass as a large truck.
White dwarfs do not have any fuel left, but they glow faintly from left over energy.
When a white dwarf stops glowing it is dead. Then it is called a black dwarf.

70. BLACK DWARF

71. Neutron Star A dying giant or super giant can suddenly explode.
Within hours, the star blazes millions of times brighter.
This explosion is called a supernova.

72. Supernova

74. Supernova
After a supernova, some of the material from the star expands into space.
This material may become apart of a nebula
The nebula can then contract to form a new “recycled” star.
Astronomers think the sun began as a nebula that contained material from a supernova explosion.

75. Neutron Star
After the star explodes, some of the material from the star is left behind.
This material forms a Neutron Star.
Neutron stars are even smaller and more dense than white dwarfs.
A neutron star may contain as much as 3 times the mass of the sun, but only be about 20 kilometers wide.

76. Black Holes
The most massive stars – those having more than 40 times the mass of the sun- become black holes when they die.
After this kind of star supernovas more than 5 times the mass of the sun may be left. The gravity of this mass is so strong that the gas is pulled inward, packing the gas into a smaller and smaller space.
Eventually 5 times the mass of the sun becomes packed into a area with a diameter of 30 kilometers.
At that point, the gravity is so strong that nothing can escape, not even light.
The remains of the star is a black hole.

83. Pulsars
In 1967 Jocelyn Bell detected an object in space that gave off radio waves (Some people thought they were messages from aliens).
Astronomers discovered that the source was a neutron star. A small object that is left over when a giant star explodes.
Neutron stars that pulsate radio waves are called PULSARS.

84. Quasars
Quasars are very bright, but also very far away approximately 12 billion light years.
What could be so far away yet so bright?
Astronomers believe that quasars are distant galaxies with black holes as their centers with the black hole having a mass that is a billion times that of the sun.
As the enormous amounts of gas revolve around such a black hole, the gas heats up and shines brightly.

85. Milky Way Galaxy

86. Star Systems and Galaxies
More than half of all stars are members of groups of 2 or more stars called star systems.
Stars with two stars are called double stars or binary stars.
Those with three stars are called triple stars.

87. Eclipsing binary is where one star blocks out the light from another.
Astronomers are have found other stars with planets around them. They are able to tell that these stars have planets because of how the planet effects the star.
Only large planets have been detected so far (half the mass of Jupiter). A small planet would be difficult to detect because it would have little gravitational effect on the star it revolved around.

88. 3 types of Galaxies Spiral Galaxies: Has the shape of twin spirals.
Elliptical Galaxies: Look like flattened balls. These galaxies have billions of stars, but little gas and dust. Because of the little gas and dust new stars cannot form, so most elliptical galaxies contain old stars.
Irregular Galaxies: Do not have regular shapes.

89. Spiral Galaxy

90. Elliptical Galaxy

91. Irregular Galaxy
Discovered by E.E. Barnard in 1884, NGC 6822 is also known as Barnard's Galaxy. It is located 1.6 million light-years away in the constellation Sagittarius. In this image, taken by the 4-meter Blanco Telescope in Chile, the galaxy glows blue with the light of countless massive, hot stars. Pinkish bubble nebulae hang along the galaxy's fringes.

92. Big Bang
10 to 15 billion years ago the universe was a single point that was hot and dense.
A enormous explosion formed the universe about 10 to 15 billion years ago.
The universe is continuously expanding and getting larger.

93. Formation of Our Solar System
As the universe grew, gas and dust spread out in our galaxy.
About 5 billion years ago, a giant cloud of gas and dust, or nebula, collapsed to form the solar system.
Slowly the nebula shrank to form a spinning disk. As gravity pulled some of the gas into the center of the disk, the gas became hot and dense enough for nuclear fusion to begin and the sun was born.
Elsewhere in the disk the gas and dust formed the planets.

96. Future of the Universe
One Theory: It will continue to expand and all of the stars will run out of fuel and burn out and the Universe will be cold and dark.
Second Theory: It will begin to come back together and be called the “big crunch.” All the matter of the universe will be crushed into an enormous black hole.

97. Future of the Universe
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