1. Electromagnetic Radiation And Stars and Galaxies
Chapter 15 & 26
Electromagnetic Radiation
And
Stars and Galaxies

2. Chapter 15 ~ Electromagnetic Radiation I
Chapter 15 ~ Electromagnetic Radiation I. What are electromagnetic waves? A. Electromagnetic Waves  waves created by vibrating electric charges, can travel through a vacuum or through matter, and have a wide variety of frequencies and wavelengths. B. Radiant Energy → energy carried by electromagnetic waves.

3. Longest Shortest II. The Electromagnetic Spectrum
A. Radio Waves → low-frequency E.M. waves with wavelengths longer than about 1 mm; used for communication.
B. Microwaves → radio waves with wavelengths of between about 1 m and 1 mm; widely used in communication for cell phones and satellite signals, and to heat your food.
C. Infrared Waves → E.M. waves with wavelengths between about one mm and 750 billionths of a meter; used in remote controls, and computers reading CDs.
Shortest

4. Longest
D. Visible Light → E.M. waves with wavelengths of 750 to 400 billionths of a meter that can be detected by human eyes.
1. What color has the longest wavelength? Red
2. What color has the shortest wavelength? Violet
E. Ultraviolet Waves → E.M. waves with wavelengths between about 400 billionths and 10 billionths of a meter; can damage skin cells and cause cancer, and kills bacteria.
Shortest

5. Longest
F. X-rays → E.M. waves with wavelengths between about 10 billionths of a meter and 10 trillionths of a meter; often used for medical imaging.
G. Gamma Rays → E.M. waves with no mass and no charge that travels at the speed of light and is usually emitted with alpha or beta particles from a decaying atomic nucleus; has a wavelength less than about 10 trillionths of a meter.
Shortest

6. The Electromagnetic Spectrum

7. Chapter 26 ~ Stars and Galaxies I
Chapter 26 ~ Stars and Galaxies I. Observing the Universe (Page 822 only) A. The light from stars and other objects can provide information about the star's composition, its temperature, and even how fast it is moving toward or away from Earth. B. The wavelengths of visible light emitted by a star depend on the star's temperature and composition.

8. C. Spectroscope → a device that disperses light into its component wavelengths, using a prism or diffraction grating. D. The separated wavelengths are called the spectrum of the star. E. What is the fastest thing in the universe? light F. How fast does it travel in space? 300,000km/s

9. G. To measure enormous distances in space, astronomers use a unit called the light-year.
Light-Year → the distance light travels in one year; it is about 9.5 trillion kilometers.

10. II. Evolution of Stars
A. Review Vocabulary: Nuclear Fusion → a nuclear reaction in which atomic nuclei join together.
B. How do stars form?
1. Stars begin as a nebula, a large cloud of gas, ice and dust.
2. Gravity causes the nebula to (expand, contract).
3. A protosun forms at the center of the cloud when the temperature reaches 1 million Kelvin.

11. 4. When the temperature reaches 10 million K, nuclear fusion of hydrogen into helium begins, and a star is born.
C. H-R Diagram
1. A star's brightness and temperature are plotted on an H-R Diagram.
2. Main Sequence → section of the H-R diagram that is plotted from the upper left to the lower right and contains 90% of all known stars.

13. D. How do stars change?
1. Our Sun is a main sequence star.
2. The life cycle of a main sequence star:
a. Nebula
b. Main sequence star
c. Red Giant  a late stage in a star’s life cycle that occurs when its hydrogen fuel is used up, its core contracts, and its outer layers expand and cool.

14. d. White dwarf  the white hot, dense core of a star that has lost its outer layers and continues to contract under gravity.
e. Black dwarf ­ the final stage of a main sequence star’s life.

15. 3. The life cycle of a massive main sequence star:
a. Nebula
b. Massive main sequence star  stars that are over 8 times more massive than our Sun.
c. Supergiant  a late stage in a massive star’s life cycle that occurs when its hydrogen fuel is used up, its core contracts, and its outer layers expand and cool.

16. d. Supernova  a late stage in a massive star’s life cycle when the core collapses violently and the outer portion of the star explodes. OR
Neutron Star  the collapsed core of a supernova that can shrink to about 20 km in diameter and contains only neutrons in the dense core.
Black Hole  the final stage in the life cycle of a massive star, where the core’s mass collapses to a point that it’s gravity is so strong that not even light can escape.

17. Life of a Star

18. E. The Sun – A Main Sequence Star
1. The Sun is made mostly of hydrogen and helium.
2. The Sun contains about 99% of all the mass in the solar system.
3. Core the center of the sun; here is where nuclear fusion occurs; made of plasma.
4. Radiation Zone matter here is still plasma; the energy produced in the core is transferred away by electromagnetic radiation.

19. 5. Convection Zone  the Sun’s outer layer; energy is transferred from the top of the radiation zone to the surface by thermal convection.
6. Photosphere  the visible surface of the Sun; emits the light that we see.
7. Sunspot  a dark area of the photosphere that is cooler than the surrounding areas; caused by regions of strong magnetic fields.

20. 8. Prominences  huge arching columns of gas caused by intense magnetic fields associated with sunspots. 9. Solar Flares  gases near a sunspot sometimes brighten suddenly, shooting gas outward at high speeds.

23. 10. Aurora  light produced around the polar regions that is caused by high-energy particles from the Sun interacting with Earth’s atmosphere. a. What are they called in the northern hemisphere? Aurora Borealis b. What are they called in the southern hemisphere? Aurora Australis

24. III. Galaxies and the Milky Way
A. Galaxy → a large group of stars, gas, and dust held together by gravity. B. Milky Way → a spiral galaxy that is about 100,000 light-years in diameter and contains from 200 to 400 billion stars, including the Sun.

25. C. Spiral Galaxy → a galaxy that is disk-shaped and usually has arms that wind outward from the galaxy's center.
* List two examples: Milky Way Galaxy and Andromeda Galaxy

26. D. Elliptical Galaxy → a galaxy that has a round, elliptical shape.

27. E. Irregular Galaxy → a galaxy that has no definite shape.
* List two examples: Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC)

28. F. Local Group → a cluster of about 50 galaxies, including the Milky Way Galaxy. IV. Cosmology → the study of how the universe began, what it is made of, and how it continues to evolve. A. Big Bang Theory → a theory that about 13.7 billion years ago, the entire universe was contained in a single point that began expanding outward.

29. The speed and direction of motion of galaxies can be determined by the Doppler effect.
C. As the source approaches, wavelengths become (longer, shorter).
D. As the source moves away, wavelengths become (longer, shorter).
E. As a galaxy approaches, the light is blueshifted.
F. As a galaxy moves away, the light is redshifted.
G. The Hubble redshift is caused by the expansion of space and the entire universe.

30. The Doppler Shift