1. Light and Matter: Reading Messages from the Cosmos
© 2014 Pearson Education, Inc. 1

2. 5.1 Light in Everyday Life Our goals for learning:
How do we experience light?
How do light and matter interact?
© 2014 Pearson Education, Inc.

3. Light
Much of the information we get in astronomy is carried by “light”.
© 2014 Pearson Education, Inc.

4. What information does “light” contain?
Location of light in the sky...gives position of a planet, moon, or star.
Color…gives temperature, speed, and direction of motion, chemical composition.
Brightness…gives distance, composition, periods of motion (from changes).
Size of light…gives size and distance information.
© 2014 Pearson Education, Inc.

5. Speed of light in empty space is constant
Properties of Light
Speed of light in empty space is constant
C=3*10^8 m/s = 670 billion mph
This finite speed has a real effect on information carried by light
© 2014 Pearson Education, Inc.

6. It takes 1 ¼ sec for light to reach us from the moon.
Properties of Light
It takes 1 ¼ sec for light to reach us from the moon.
It takes 8 1/3 minutes for light to reach us from the sun.
It takes 4 1/3 years for light to reach us from the nearest star.
© 2014 Pearson Education, Inc.

7. How do we experience light?
The warmth of sunlight tells us that light is a form of energy.
We can measure the flow of energy in light in units of watts: 1 watt = 1 joule/s.
© 2014 Pearson Education, Inc.

8. Colors of Light White light is made up of many different colors.
Newton showed that white light is composed of all the colors of the rainbow.
White light is made up of many different colors.
© 2014 Pearson Education, Inc.

9. How do light and matter interact?
Emission
Absorption
Transmission
Transparent objects transmit light.
Opaque objects block (absorb) light.
Reflection/scattering
© 2014 Pearson Education, Inc.

10. Reflection and Scattering
Mirror reflects light in a particular direction.
Movie screen scatters light in all directions.
© 2014 Pearson Education, Inc.

11. Interactions of Light with Matter
Interactions between light and matter determine the appearance of everything around us.
© 2014 Pearson Education, Inc.

12. Thought Question Why is a rose red? The rose absorbs red light.
The rose transmits red light.
The rose emits red light.
The rose reflects red light.
© 2014 Pearson Education, Inc.

13. Thought Question Why is a rose red? The rose absorbs red light.
The rose transmits red light.
The rose emits red light.
The rose reflects red light.
© 2014 Pearson Education, Inc. 13

14. What have we learned? How do we experience light?
Light is a form of energy.
Light comes in many colors that combine to form white light.
How do light and matter interact?
Matter can emit light, absorb light, transmit light, and reflect (or scatter) light.
Interactions between light and matter determine the appearance of everything we see.
© 2014 Pearson Education, Inc.

15. 5.2 Properties of Light Our goals for learning: What is light?
What is the electromagnetic spectrum?
© 2014 Pearson Education, Inc.

16. What is light? Light can act either like a wave or like a particle.
Particles of light are called photons.
© 2014 Pearson Education, Inc.

17. Waves
A wave is a pattern of motion that can carry energy without carrying matter along with it.
© 2014 Pearson Education, Inc.

18. Gamma Waves X-Rays Wave Types
Waves emitted from radioactive nuclei, highly penetrating, very harmful to humans
X-Rays
Waves emitted when high energy electrons bombard metal, used to diagnose internal injuries and treat certain cancers-overexposure is harmful to humans.
© 2014 Pearson Education, Inc.

19. Wave Types Ultraviolet
Waves which cause sunburn-ozone is our atmosphere converts UV radiation to heat, can cause skin cancer in humans.
Visible Light
Wavelengths detected by the human eye, caused by electrons moving between orbitals in atoms, violet is the shortest wavelength and red is the longest.
Violet-Indigo-Blue-Green-Yellow-Orange-Red
© 2014 Pearson Education, Inc.

20. Wave Types
Infrared
Waves produced by hot bodies, they are readily absorbed and cause the material’s atoms to vibrate, generating heat- usefully in astronomy and in physical therapy.
Radio Waves
Waves produced by charged matter being accelerated, types include AM/FM radio, TV, Microwaves, and radar – useful in astronomy, communication, and have domestic applications.
© 2014 Pearson Education, Inc.

21. Continuous Spectrum Emission Lines Spectrum Analysis
White light spread out by a prism showing all the wavelengths of visible light.
Emission Lines
Specific wavelengths emitted when an atom’s electrons are excited and then jump back to their lowest energy level – unique for each type of atom.
© 2014 Pearson Education, Inc.

22. Fraunhofer Lines Absorption Lines Spectrum Analysis
Discovered in 1817 – absorption lines in a star’s spectrum
Absorption Lines
Wavelengths missing from a spectrum caused by the absorption of those wavelengths
Shows the COMPOSITION of the object being studied.
© 2014 Pearson Education, Inc.

23. Doppler Effect Spectrum Analysis
The compression or stretching of an object’s absorption spectrum caused by the relative movement of the object – First identified with the sound waves
Shows DIRECTION
Red Shifting – Moving away
Blue Shifting – Moving towards
© 2014 Pearson Education, Inc.

24. Wave speed = wavelength x frequency
Properties of Waves
Wavelength is the distance between two wave peaks.
Frequency is the number of times per second that a wave vibrates up and down.
Wave speed = wavelength x frequency
© 2014 Pearson Education, Inc.

25. Light: Electromagnetic Waves
A light wave is a vibration of electric and magnetic fields.
Light interacts with charged particles through these electric and magnetic fields.
© 2014 Pearson Education, Inc.

26. Light
Think of light as waves.
© 2014 Pearson Education, Inc.

27. Wavelength and Frequency
wavelength x frequency = speed of light = constant
© 2014 Pearson Education, Inc.

28. Particles of Light Particles of light are called photons.
Each photon has a wavelength and a frequency.
The energy of a photon depends on its frequency.
© 2014 Pearson Education, Inc.

29. Each wave is moving at the same speed.
© 2014 Pearson Education, Inc.

30. Wavelength – the distance between wave crests.
Properties of Light
Wavelength – the distance between wave crests.
Wavelength is indicated by the Greek symbol “λ” in the figure above.
Frequency = number of wave crests per second passing a point.
© 2014 Pearson Education, Inc.

31. Wavelength, Frequency, and Energy
l x f = c
l = wavelength, f = frequency
c = 3.00 x 108 m/s = speed of light
E = h x f = photon energy
h = x joule x s = Planck's constant
© 2014 Pearson Education, Inc.

32. Special Topic: Polarized Sunglasses
Polarization describes the direction in which a light wave is vibrating.
Reflection can change the polarization of light.
Polarized sunglasses block light that reflects off of horizontal surfaces.
© 2014 Pearson Education, Inc.

33. Color is determined by wavelength or frequency of light
Properties of Light
Color is determined by wavelength or frequency of light
We can divide light or electromagnetic radiation by wavelength (color), we create a spectrum.
This is called the Electromagnetic Spectrum
© 2014 Pearson Education, Inc.

34. What is the electromagnetic spectrum?
© 2014 Pearson Education, Inc.

35. The Electromagnetic Spectrum
© 2014 Pearson Education, Inc.

36. Electromagnetic Spectrum
© 2014 Pearson Education, Inc.

37. Electromagnetic Spectrum
Visible light is actually a very small part of the spectrum
We can see the colors within the sunlight because each color is bent differently when it passes through a prism.
© 2014 Pearson Education, Inc.

38. Why do we see visible light?
1. Sun emits most strongly at these wavelengths
2. Earth’s atmosphere blocks many other wavelengths
3. Human eye efficiently detects available light.
© 2014 Pearson Education, Inc.

39. Thought Question The higher the photon energy,
the longer its wavelength.
the shorter its wavelength.
energy is independent of wavelength.
© 2014 Pearson Education, Inc.

40. Thought Question The higher the photon energy,
the longer its wavelength.
the shorter its wavelength.
energy is independent of wavelength.
© 2014 Pearson Education, Inc. 40

41. What have we learned? What is light?
Light can behave like either a wave or a particle.
A light wave is a vibration of electric and magnetic fields.
Light waves have a wavelength and a frequency.
Photons are particles of light.
What is the electromagnetic spectrum?
Human eyes cannot see most forms of light.
The entire range of wavelengths of light is known as the electromagnetic spectrum.
© 2014 Pearson Education, Inc.

42. 5.3 Properties of Matter Our goals for learning:
What is the structure of matter?
What are the phases of matter
How is energy stored in atoms?
© 2014 Pearson Education, Inc.

43. What is the structure of matter?
Use this figure to define the nucleus; protons, neutrons, electrons; scale of atom and "electron cloud."
© 2014 Pearson Education, Inc.

44. Atomic Terminology Atomic number = # of protons in nucleus
Atomic mass number = # of protons + neutrons
Molecules: consist of two or more atoms (H2O, CO2)
© 2014 Pearson Education, Inc.

45. Atomic Terminology
Isotope: same # of protons but different # of neutrons (4He, 3He)
© 2014 Pearson Education, Inc.

46. What are the phases of matter?
Familiar phases:
Solid (ice)
Liquid (water)
Gas (water vapor)
Phases of same material behave differently because of differences in chemical bonds.
© 2014 Pearson Education, Inc.

47. Phase Changes
Ionization: stripping of electrons, changing atoms into plasma
Dissociation: breaking of molecules into atoms
Evaporation: breaking of flexible chemical bonds, changing liquid into solid
Melting: breaking of rigid chemical bonds, changing solid into liquid
© 2014 Pearson Education, Inc.

48. Phases and Pressure
Phase of a substance depends on both temperature and pressure.
Often more than one phase is present.
© 2014 Pearson Education, Inc.

49. How is energy stored in atoms?
Excited states
Ground state
Electrons in atoms are restricted to particular energy levels.
© 2014 Pearson Education, Inc.

50. Energy Level Transitions
The only allowed changes in energy are those corresponding to a transition between energy levels.
Not allowed
Allowed
© 2014 Pearson Education, Inc.

51. What have we learned? What is the structure of matter?
Matter is made of atoms, which consist of a nucleus of protons and neutrons surrounded by a cloud of electrons.
What are the phases of matter?
Adding heat to a substance changes its phase by breaking chemical bonds.
As temperature rises, a substance transforms from a solid to a liquid to a gas, then the molecules can dissociate into atoms.
Stripping of electrons from atoms (ionization) turns the substance into a plasma.
© 2014 Pearson Education, Inc.

52. What have we learned? How is energy stored in atoms?
The energies of electrons in atoms correspond to particular energy levels.
Atoms gain and lose energy only in amounts corresponding to particular changes in energy levels.
© 2014 Pearson Education, Inc.

53. 5.4 Learning from Light Our goals for learning:
What are the three basic types of spectra?
How does light tell us what things are made of?
How does light tell us the temperatures of planets and stars?
How does light tell us the speed of a distant object?
© 2014 Pearson Education, Inc.

54. What are the three basic types of spectra?
Spectra of astrophysical objects are usually combinations of these three basic types.
© 2014 Pearson Education, Inc.

55. What are the three basic types of spectra?
This tool from the Light and Spectroscopy tutorial.
© 2014 Pearson Education, Inc.

56. Three Types of Spectra
© 2014 Pearson Education, Inc.

57. Continuous Spectrum
The spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption.
© 2014 Pearson Education, Inc.

58. Emission Line Spectrum
A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines.
© 2014 Pearson Education, Inc.

59. Absorption Line Spectrum
A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.
© 2014 Pearson Education, Inc.

60. How does light tell us what things are made of?
© 2014 Pearson Education, Inc.

61. Chemical Fingerprints
Each type of atom has a unique set of energy levels.
Each transition corresponds to a unique photon energy, frequency, and wavelength.
© 2014 Pearson Education, Inc.

62. Chemical Fingerprints
Downward transitions produce a unique pattern of emission lines.
© 2014 Pearson Education, Inc.

63. Chemical Fingerprints
This tool from the Light and Spectroscopy tutorial.
© 2014 Pearson Education, Inc.

64. Chemical Fingerprints
Because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths.
© 2014 Pearson Education, Inc.

65. Chemical Fingerprints
This tool from the Light and Spectroscopy tutorial.
© 2014 Pearson Education, Inc.

66. Chemical Fingerprints
Each type of atom has a unique spectral fingerprint.
© 2014 Pearson Education, Inc.

67. Chemical Fingerprints
Observing the fingerprints in a spectrum tells us which kinds of atoms are present.
Note that students may not be familiar with the notation concerning ions, especially since the book does it slightly differently in the text than it does in this figure, (i.e. +2 vs. ++) so this may need to be explained.
© 2014 Pearson Education, Inc.

68. Chemical Fingerprints
Example: Solar Spectrum
You can use this slide as an example of real astronomical spectra made from a combination of the idealized types. Here we have the continuous (thermal) spectrum from the solar interior; dark absorption lines where the cooler solar atmosphere (photosphere) absorbs specific wavelengths of light.
© 2014 Pearson Education, Inc.

69. Energy Levels of Molecules
Molecules have additional energy levels because they can vibrate and rotate.
© 2014 Pearson Education, Inc.

70. Energy Levels of Molecules
The large numbers of vibrational and rotational energy levels can make the spectra of molecules very complicated.
Many of these molecular transitions are in the infrared part of the spectrum.
© 2014 Pearson Education, Inc.

71. Thought Question Which letter(s) label(s) absorption lines?
© 2014 Pearson Education, Inc.

72. Thought Question Which letter(s) label(s) absorption lines? 72
© 2014 Pearson Education, Inc. 72

73. Thought Question
Which letter(s) label(s) the peak (greatest intensity) of infrared light?
© 2014 Pearson Education, Inc.

74. Thought Question
Which letter(s) label(s) the peak (greatest intensity) of infrared light?
© 2014 Pearson Education, Inc.

75. Thought Question Which letter(s) label(s) emission lines?
© 2014 Pearson Education, Inc.

76. Thought Question Which letter(s) label(s) emission lines?
© 2014 Pearson Education, Inc.

77. How does light tell us the temperatures of planets and stars?
© 2014 Pearson Education, Inc.

78. Thermal Radiation
Nearly all large or dense objects emit thermal radiation, including stars, planets, you.
An object's thermal radiation spectrum depends on only one property: its temperature.
© 2014 Pearson Education, Inc.

79. Properties of Thermal Radiation
Hotter objects emit more light at all frequencies per unit area.
Hotter objects emit photons with a higher average energy.
Remind students that the intensity is per area; larger objects can emit more total light even if they are cooler.
© 2014 Pearson Education, Inc.

80. Wien's Law
Remind students that the intensity is per area; larger objects can emit more total light even if they are cooler.
© 2014 Pearson Education, Inc.

81. Thought Question Which is hottest? a blue star a red star
a planet that emits only infrared light
© 2014 Pearson Education, Inc.

82. Thought Question Which is hottest? a blue star a red star
a planet that emits only infrared light
© 2014 Pearson Education, Inc.

83. Thought Question Why don't we glow in the dark?
People do not emit any kind of light.
People only emit light that is invisible to our eyes.
People are too small to emit enough light for us to see.
People do not contain enough radioactive material.
© 2014 Pearson Education, Inc.

84. Thought Question Why don't we glow in the dark?
People do not emit any kind of light.
People only emit light that is invisible to our eyes.
People are too small to emit enough light for us to see.
People do not contain enough radioactive material.
© 2014 Pearson Education, Inc.

85. Example: How do we interpret an actual spectrum?
By carefully studying the features in a spectrum, we can learn a great deal about the object that created it.
© 2014 Pearson Education, Inc.

86. What is this object?
Reflected sunlight: Continuous spectrum of visible light is like the Sun's except that some of the blue light has been absorbed—object must look red.
© 2014 Pearson Education, Inc.

87. What is this object?
Thermal radiation: Infrared spectrum peaks at a wavelength corresponding to a temperature of 225 K.
© 2014 Pearson Education, Inc.

88. What is this object?
Carbon dioxide: Absorption lines are the fingerprint of CO2 in the atmosphere.
© 2014 Pearson Education, Inc.

89. What is this object?
Ultraviolet emission lines: Indicate a hot upper atmosphere
© 2014 Pearson Education, Inc.

90. What is this object?
Mars!
© 2014 Pearson Education, Inc.

91. How does light tell us the speed of a distant object?
This figure from the book can give an introduction to the Doppler effect.
© 2014 Pearson Education, Inc.

92. The Doppler Effect
This and the following slides are tools from the Doppler Effect tutorial.
© 2014 Pearson Education, Inc.

93. The Doppler Effect
Same for Light
© 2014 Pearson Education, Inc.

94. Measuring the Shift
Stationary
Moving away
Away faster
Moving toward
Toward faster
We generally measure the Doppler effect from shifts in the wavelengths of spectral lines.
© 2014 Pearson Education, Inc.

95. Measuring the Shift
The amount of blueshift or redshift tells us an object's speed toward or away from us.
© 2014 Pearson Education, Inc.

96. Measuring the Shift
Doppler shift tells us ONLY about the part of an object's motion toward or away from us:
© 2014 Pearson Education, Inc.

97. Thought Question
I measure a line in the lab at nm. The same line in a star has wavelength nm. What can I say about this star?
It is moving away from me.
It is moving toward me.
It has unusually long spectral lines.
© 2014 Pearson Education, Inc.

98. Thought Question
I measure a line in the lab at nm. The same line in a star has wavelength nm. What can I say about this star?
It is moving away from me.
It is moving toward me.
It has unusually long spectral lines.
© 2014 Pearson Education, Inc. 98

99. Measuring the Shift Measuring Redshift
More tools from the Doppler shift tutorial.
© 2014 Pearson Education, Inc.

100. Measuring the Shift
Measuring Redshift
© 2014 Pearson Education, Inc.

101. Measuring the Shift
Measuring Velocity
© 2014 Pearson Education, Inc.

102. Measuring the Shift
Measuring Velocity
© 2014 Pearson Education, Inc.

103. Rotation Rates
Different Doppler shifts from different sides of a rotating object spread out its spectral lines.
© 2014 Pearson Education, Inc.

104. Spectrum of a Rotating Object
Spectral lines are wider when an object rotates faster.
© 2014 Pearson Education, Inc.

105. What have we learned? What are the three basic type of spectra?
Continuous spectrum, emission line spectrum, absorption line spectrum
How does light tell us what things are made of?
Each atom has a unique fingerprint.
We can determine which atoms something is made of by looking for their fingerprints in the spectrum.
© 2014 Pearson Education, Inc.

106. What have we learned?
How does light tell us the temperatures of planets and stars?
Nearly all large or dense objects emit a continuous spectrum that depends on temperature.
The spectrum of that thermal radiation tells us the object's temperature.
How does light tell us the speed of a distant object?
The Doppler effect tells us how fast an object is moving toward or away from us.
© 2014 Pearson Education, Inc.