1. 24.1 The Study of Light Electromagnetic Radiation
 Electromagnetic radiation includes gamma rays, X-rays, ultraviolet light, visible light, infrared radiation, microwaves, and radio waves.
 The electromagnetic spectrum is the arrangement of electromagnetic radiation according to wavelength.

2. Electromagnetic Spectrum
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3. Electromagnetic Spectrum
All electromagnetic radiation travels through space at 300,000 kilometers/second (180,000 miles/second) – the speed of light.
Notice the human eye can only see a small amount of what
electromagnetic radiation is all around us.
Analyzing electromagnetic radiation tells us most of what we know about the universe.
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4. Electromagnetic Spectrum
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5. Electromagnetic Spectrum
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Radio waves, microwaves, x-rays, gamma rays, and the spectrum of visible colors are all really the same thing - electromagnetic energy. The differences are their wavelengths. Radio waves are long, measuring as much as hundreds of meters between peaks. Gamma ray wavelengths are extremely short, as little as trillionths of a meter. A photon of shorter-wavelength light packs more energy than a photon of longer-wavelength light.

6. 24.1 The Study of Light The Doppler Effect
 The Doppler effect is the apparent change in frequency of electromagnetic or sound waves caused by the relative motions of the source and the observer.
 In astronomy, the Doppler effect is used to determine whether a star or other body in space is moving away from or toward Earth.

7. The Doppler Effect
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8. Structure of the Sun
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9. 24.3 The Sun The Solar Interior  Nuclear Fusion
• Nuclear fusion is the way that the sun produces energy. This reaction converts four hydrogen nuclei into the nucleus of a helium atom, releasing a tremendous amount of energy.
• During nuclear fusion, energy is released because some matter is actually converted to energy.
• It is thought that a star the size of the sun can exist in its present stable state for 10 billion years. As the sun is already 4.5 billion years old, it is “middle-aged.”

10. Nuclear Fusion
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11. 24.3 The Sun Structure of the Sun  Corona
• The corona is the outer, weak layer of the solar atmosphere.
• The temperature at the top of the corona exceeds 1 million K.
• Solar wind is a stream of protons and electrons ejected at high speed from the solar corona.

12. 24.3 The Sun The Active Sun  Sunspots
• A sunspot is a dark spot on the sun that is cool in contrast to the surrounding photosphere.
• Sunspots appear dark because of their temperature, which is about 1500 K less than that of the surrounding solar surface.

13. Sunspots
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14. 24.3 The Sun The Active Sun  Prominences
• Prominences are huge cloudlike structures consisting of chromospheric gases.
• Prominences are ionized gases trapped by magnetic fields that extend from regions of intense solar activity.

15. Solar Prominence
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16. 24.3 The Sun The Active Sun  Solar Flares
• Solar flares are brief outbursts that normally last about an hour and appear as a sudden brightening of the region above a sunspot cluster.
• During their existence, solar flares release enormous amounts of energy, much of it in the form of ultraviolet, radio, and X-ray radiation.
• Auroras, the result of solar flares, are bright displays of ever-changing light caused by solar radiation interacting with the upper atmosphere in the region of the poles.

17. Aurora Borealis
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18. 17.2 Heating the Atmosphere
Energy Transfer as Heat
17.2 Heating the Atmosphere
 Heat is the energy transferred from one object to another because of a difference in the objects’ temperature.
 Temperature is a measure of the average kinetic energy of the individual atoms or molecules in a substance.

19. 17.2 Heating the Atmosphere
Energy Transfer as Heat
17.2 Heating the Atmosphere
 Three mechanisms of energy transfer as heat are conduction, convection, and radiation.
 Conduction
• Conduction is the transfer of heat through matter by molecular activity.
 Convection
• Convection is the transfer of heat by mass movement or circulation within a substance.

20. 17.2 Heating the Atmosphere
Energy Transfer as Heat
17.2 Heating the Atmosphere
 Radiation
• Radiation is the transfer of energy (heat) through space by electromagnetic waves that travel out in all directions.
• Unlike conduction and convection, which need material to travel through, radiant energy can travel through the vacuum of space.

21. Energy Transfer as Heat
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22. 17.2 Heating the Atmosphere
Energy Transfer as Heat
17.2 Heating the Atmosphere
 Electromagnetic Waves
• The sun emits light and heat as well as the ultraviolet rays that cause a suntan. These forms of energy are only part of a large array of energy emitted by the sun, called the electromagnetic spectrum.

23. Electromagnetic Spectrum
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24. Visible Light Consists of an Array of Colors
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25. 17.2 Heating the Atmosphere
Energy Transfer as Heat
17.2 Heating the Atmosphere
 Radiation
• All objects, at any temperature, emit radiant energy.
• Hotter objects radiate more total energy per unit area than colder objects do.
• The hottest radiating bodies produce the shortest wavelengths of maximum radiation.
• Objects that are good absorbers of radiation are good emitters as well.

26. 17.2 Heating the Atmosphere
What Happens to Solar Radiation?
17.2 Heating the Atmosphere
 When radiation strikes an object, there usually are three different results.
1. Some energy is absorbed by the object.
2. Substances such as water and air are transparent to certain wavelengths of radiation.
3. Some radiation may bounce off the object without being absorbed or transmitted.

27. Solar Radiation
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28. 17.2 Heating the Atmosphere
What Happens to Solar Radiation?
17.2 Heating the Atmosphere
 Reflection and Scattering
• Reflection occurs when light bounces off an object. Reflection radiation has the same intensity as incident radiation.
• Scattering produces a larger number of weaker rays that travel in different directions.

29. 17.2 Heating the Atmosphere
What Happens to Solar Radiation?
17.2 Heating the Atmosphere
 Absorption
• About 50 percent of the solar energy that strikes the top of the atmosphere reaches Earth’s surface and is absorbed.
• The greenhouse effect is the heating of Earth’s surface and atmosphere from solar radiation being absorbed and emitted by the atmosphere, mainly by water vapor and carbon dioxide.

30. 17.3 Temperature Controls Why Temperatures Vary
 Cloud Cover and Albedo
• Albedo is the fraction of total radiation that is reflected by any surface.
• Many clouds have a high albedo and therefore reflect back to space a significant portion of the sunlight that strikes them.

31. Clouds Reflect and Absorb Radiation
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