Lesson 207: STARS AND STELLAR EVOLUTION 207 Stars.pdf · Define parallax and explain how...

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Printed on 2/23/2014 1 Lesson 207: STARS AND STELLAR EVOLUTION Stars are the ultimate source of all matter and energy found on Earth. Sudents will learn the characteristics of stars, the types of stars, and the stages of a star development. Fundamental Questions Attempting to give thorough and reasonable answers to the following questions will help you gauge your level of understanding this lesson. Students that can confidently answer these questions have mastered the concepts of this lesson. 1. Which type of star is the most powerful? 2. If you could be any type of star, what kind would you be and why? 3. Explain how a black hole can have less mass than a supergiant star, but still have more gravity. 4. Why are giant and supergiant stars usually red? 5. Why are small main-sequence stars usually red? 6. Why don’t black holes and neutron stars show up on the H-R Diagram? 7. What would happen if a black hole swallowed up a hydrogen-rich, high-mass protostar? 8. Which would expect to be brighter: a low-mass white dwarf, a high-mass protostar, or a medium-mass main- sequence star? 9. How does gravity affect the development of humans? 10. Why is the sun considered the Goldilocks Star? 11. Which group is likely to be more common: black holes or white dwarfs? Lesson Objectives At the end of this lesson, students should have mastered the objectives listed below. 1. Students appreciate the importance of stars in our lives and in the existence of Earth. 2. Students understand the relationship between mass and gravity. 3. Students understand the vital role that a star’s mass (and therefore gravity) plays in its development. 4. Students understand the difficulty astronomers face in accurately classifying stars without having the luxury of watching stars change over time. 5. * Students are able to calculate the size of earth and other celestial bodies if given basic information. For example, what is the diameter of Earth if the Sun’s diameter is 1,390,000 kilometers and is 109 times larger than the Earth? 6. Students are familiar with the characteristics of our sun, including its age, size, surface temperature, core temperature, stage of development, location in our galaxy, and its color. 7. Students should be familiar with the size differences between Earth, the Sun, and all other types of stars. 8. Students should know that the distance between Earth and the Sun is about 150,000,000 kilometers (which is equal to 93,000,000 miles). 9. Students can list the elements that are common in stars and can approximate the chemical composition of the remnants of low-, medium-, and high-mass stars. 10. Students can place the types of stars in order of increasing density and increasing mass. 11. Students can determine the surface temperature of a star based on the star’s color, and vice versa. 12. Students can identify the three characteristics that affect a star’s brightness. 13. Students can use the Hertzsprung-Russell Diagram to determine the absolute magnitude, the surface temperature, the color, or the type of a star. 14. Students recognize that 90% of all known stars are main-sequence stars. 15. Students understand the relationship between surface temperature and absolute magnitude for the different classes of stars. 16. Students can describe the three methods used by astronomers to measure star distances. 17. Students can describe the process of nuclear fusion explain why it is important to the development of stars. 18. Students can give detailed descriptions of the “lives” of low-, medium-, and high-mass stars. 19. Students understand the relationship between a gas’ volume and its temperature (Charles' Law). Important Terms The following terms are some of the vocabulary that students should be familiar with in order to fully master this lesson. 1. Diameter 2. Main-sequence star 3. Giant stars 4. Supergiant stars 5. Betelgeuse 6. White dwarfs 7. Black dwarfs 8. Neutron stars 9. Neutron 10. Black holes 11. Event horizon 12. Spectroscope 13. Hydrogen (H) 14. Helium (He) 15. Carbon (C) 16. Iron (Fe) 17. Surface temperatures 18. Apparent magnitude 19. Absolute magnitude 20. Variable stars 21. H-R Diagram 22. Parallax 23. Red shift 24. Nuclear fusion 25. Nebula 26. Protostar 27. Planetary/ring nebula 28. Charles' Law

Transcript of Lesson 207: STARS AND STELLAR EVOLUTION 207 Stars.pdf · Define parallax and explain how...

Page 1: Lesson 207: STARS AND STELLAR EVOLUTION 207 Stars.pdf · Define parallax and explain how astronomers use it to measure distances to stars. 3. Algol is a binary star system. Explain

Printed on 2/23/2014

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Lesson 207:

STARS AND STELLAR EVOLUTION Stars are the ultimate source of all matter and energy found on Earth. Sudents will learn the characteristics of

stars, the types of stars, and the stages of a star development.

Fundamental Questions

Attempting to give thorough and reasonable answers to the following questions will help you gauge your level of understanding this lesson. Students that can confidently answer these questions have mastered the concepts of this lesson.

1. Which type of star is the most powerful? 2. If you could be any type of star, what kind would you

be and why? 3. Explain how a black hole can have less mass than a

supergiant star, but still have more gravity. 4. Why are giant and supergiant stars usually red? 5. Why are small main-sequence stars usually red? 6. Why don’t black holes and neutron stars show up on

the H-R Diagram?

7. What would happen if a black hole swallowed up a hydrogen-rich, high-mass protostar?

8. Which would expect to be brighter: a low-mass white dwarf, a high-mass protostar, or a medium-mass main-sequence star?

9. How does gravity affect the development of humans? 10. Why is the sun considered the Goldilocks Star? 11. Which group is likely to be more common: black holes

or white dwarfs?

Lesson Objectives

At the end of this lesson, students should have mastered the objectives listed below.

1. Students appreciate the importance of stars in our lives and in the existence of Earth. 2. Students understand the relationship between mass and gravity. 3. Students understand the vital role that a star’s mass (and therefore gravity) plays in its development. 4. Students understand the difficulty astronomers face in accurately classifying stars without having the luxury of watching

stars change over time. 5. * Students are able to calculate the size of earth and other celestial bodies if given basic information. For example, what is

the diameter of Earth if the Sun’s diameter is 1,390,000 kilometers and is 109 times larger than the Earth? 6. Students are familiar with the characteristics of our sun, including its age, size, surface temperature, core temperature, stage

of development, location in our galaxy, and its color. 7. Students should be familiar with the size differences between Earth, the Sun, and all other types of stars. 8. Students should know that the distance between Earth and the Sun is about 150,000,000 kilometers (which is equal to

93,000,000 miles). 9. Students can list the elements that are common in stars and can approximate the chemical composition of the remnants of

low-, medium-, and high-mass stars. 10. Students can place the types of stars in order of increasing density and increasing mass. 11. Students can determine the surface temperature of a star based on the star’s color, and vice versa. 12. Students can identify the three characteristics that affect a star’s brightness. 13. Students can use the Hertzsprung-Russell Diagram to determine the absolute magnitude, the surface temperature, the

color, or the type of a star. 14. Students recognize that 90% of all known stars are main-sequence stars. 15. Students understand the relationship between surface temperature and absolute magnitude for the different classes of stars. 16. Students can describe the three methods used by astronomers to measure star distances. 17. Students can describe the process of nuclear fusion explain why it is important to the development of stars. 18. Students can give detailed descriptions of the “lives” of low-, medium-, and high-mass stars. 19. Students understand the relationship between a gas’ volume and its temperature (Charles' Law).

Important Terms

The following terms are some of the vocabulary that students should be familiar with in order to fully master this lesson.

1. Diameter 2. Main-sequence star 3. Giant stars 4. Supergiant stars 5. Betelgeuse 6. White dwarfs 7. Black dwarfs 8. Neutron stars 9. Neutron 10. Black holes

11. Event horizon 12. Spectroscope 13. Hydrogen (H) 14. Helium (He) 15. Carbon (C) 16. Iron (Fe) 17. Surface temperatures 18. Apparent magnitude 19. Absolute magnitude 20. Variable stars

21. H-R Diagram 22. Parallax 23. Red shift 24. Nuclear fusion 25. Nebula 26. Protostar 27. Planetary/ring nebula 28. Charles' Law

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Assessment Questions

The following are examples of questions that students should be able to answer. These or similar questions are likely to appear on the exam.

1. * Earth’s diameter is about 109 times smaller than the

Sun’s diameter. The Sun’s average diameter is equal to about 1,390,000 kilometers. Compute the real diameter of Earth in kilometers and then calculate the scaled size-down size of Earth compared to

2. Define parallax and explain how astronomers use it to measure distances to stars.

3. Algol is a binary star system. Explain why one star sometimes seems to disappear when astronomers observe this system.

4. Compare and contrast absolute magnitude and apparent magnitude.

5. Describe what happens to a low-mass star, a medium-mass star, and a high-mass star when each runs out of fuel.

6. Describe how the solar system is thought to have formed.

7. * Convert the distance between Earth and the Sun to feet. Show your conversions.

8. Why are stars important to humans and Earth? 9. Which group is likely to be more common: black holes

or white dwarfs? Explain your reasoning. 10. When a medium-mass star begins to run out of fuel,

what kind of star does it become? 11. What is an "event horizon"? 12. Describe how mass and gravity are related to each

other. 13. Why is mass such an important characteristic of stars? 14. Which stages of stars experience nuclear fusion? 15. How can scientists be sure that their models of stellar

evolution are accurate? 16. How do we know what elements stars are composed

of? 17. How old is our sun? 18. What kind of star is our sun?

19. * Betelgeuse has a diameter that is roughly 1,000,000 times greater than the Earth's? How many Earth's would fit into Betelgeuse? HINT: Use the formula "volume of a sphere = (4/3) · π · (r · r · r)" to help you answer this question.

20. What can astronomers learn by studying a star's color? 21. What color is a star that has a surface temperature of

10,000 degrees Celcius? 22. What is the surface temperature of a red star? 23. What is the surface temperature of our Sun? 24. Would you expect a red main-sequence star to be

bright or dim? Why? 25. * Why is parallax difficult to use for stars that are

greater than 100 light-years away? 26. What three factors determine a star's apparent

magnitude? 27. The H-R Diagram shows the relationship between what

two characteristics of stars? 28. What causes a star to die? 29. Describe the life cycle of a medium-mass star like our

Sun. 30. Why are low mass stars thought to age more slowly

than higher mass stars, even though they have less fuel?

31. What main characteristic of all stars determines the sequence of "life" it wil experience?

32. Why does a nebula tend to have more mass, but less gravity, than a black hole? Explain.

33. How far from Earth is the Sun? 34. What are the three methods used to determine the

distances to stars? 35. What is nuclear fusion is why does it produce so much

energy? 36. What happens to a gas' temperature when the gas is

compressed together?

Related Web Sites

The following are some web sites that are related to this lesson. You are encouraged to check out these sites to obtain additional information.

1. http://en.wikipedia.org/wiki/Stellar_evolution 2. http://astronomyonline.org/Stars/Evolution.asp 3. http://www.bing.com/images/search?q=stars+and+stellar+evolution&qpvt=stars+and+stellar+evolution&FORM=IGRE 4. http://www.umich.edu/~gs265/star.htm 5. http://www.astronomytoday.com/cosmology/evol.html 6. http://www.ast.cam.ac.uk/research/stars.and.stellar.evolution

Related Book Pages

The following are the pages from your book that correspond to this lesson.

Comprehensive E.S. Book Intensive/Honors E.S. Book Meteorology/GIS Book

pp. 700-714 pp. 813-825

Massachusetts Standards

The following are the Massachusetts Framework Standards that correspond to this lesson.

Earth Science Learning Standard(s) 1.1, 1.2, 2.1, 4.3

What’s Next?

Notes

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I. CHARACTERISTICS OF STARS A. Sizes of Stars

1. Main-Sequence Stars a. Stars about the same size as our sun b. The diameter of our Sun is 109 times larger than Earth’s diameter

2. Giant Stars a. Diameters 10 to 100 times bigger than the Sun b. Diameters 1000 to 10000 times bigger than Earth

3. Supergiant Stars a. Largest of all stars b. Diameters up to 1000 times the diameter of the Sun c. Life of these stars is shortest d. EXAMPLE: Betelgeuse

4. White Dwarf Stars a. Smaller than Earth b. Extremely dense c. Try to collapse into nothing, but electrical repulsion of electrons keep them from doing so d. Eventually cool off and turn into tiny frozen spheres called Black Dwarfs (or Brown Dwarfs)

5. Neutron Stars a. Smallest visible stars that have not been directly observed because they are too small b. Diameter typically less than 16 kilometers (10 miles) c. Detected using radio telescopes d. Denser than White Dwarfs (so dense that electrons combine with protons to make neutrons)

6. Black Holes a. Dead stars that have so much mass (millions times our Sun’s mass) they have collapsed under their own

gravity and may be infinitely small and infinitely dense b. Gravity is so strong that not even light can escape c. Boundary where everything gets pulled in is called the Event Horizon d. A super-massive black hole is believed to be located at the center of our galaxy

B. Composition of Stars 1. Spectroscopes are used to determine composition of stars

a. Each glowing element displays unique "fingerprint" when viewed through a spectroscope b. Scientists determine composition of stars by matching star's fingerprint to fingerprint of known elements

2. Most common elements in stars are hydrogen (H) and helium (He). a. H is lightest element in the universe. b. He is second lightest element. c. H and He account for about 96 to 99 percent of a star's mass.

3. Other elements commonly found in stars are oxygen (O), neon (Ne), carbon (C), and nitrogen (N).

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C. Surface Temperature of Stars 1. Color of a star is an indicator of how hot the surface of the star is.

a. Surface of our yellow sun is about 6000°C b. Surface of hottest (blue-white) stars is about 50,000°C c. Surface of coolest (red) stars is about 3000°C

2. The core of a star is much hotter than the surface. The core of our sun is about 15,000,000°C

Star Colors and Surface Temperatures

Star Color Average Surface Temp.

blue or blue-white 35,000 °C

white 10,000 °C

yellow 6,000 °C

red-orange 5,000 °C

red 3,000 °C

D. Brightness of Stars 1. Brightness depends on:

a. Star size b. Surface temperature c. Distance from Earth

2. Apparent Magnitude Brightness of a star when viewed from Earth

3. Absolute Magnitude Amount of light a star actually gives off

4. The brightness of most stars is constant. Stars that vary in brightness are called variable stars.

II. THE HERTZSPRUNG-RUSSELL (H-R) DIAGRAM

A. Ejnar Hertzsprung and Henry Russell independently discovered relationship between absolute magnitude and surface temperature of stars and developed diagram to study stars 1. As absolute magnitude increases, temp. increases 2. Surface temperature plotted along the horizontal (X) axis 3. Absolute magnitude plotted along vertical (Y) axis

B. Main-Sequence Stars 1. Make up 90+ percent of all stars 2. "Normal" stars 3. Long continuous band of stars that runs diagonally across H-R diagram 4. Our Sun is a main-sequence star

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III. METHODS FOR MEASURING STAR DISTANCES A. Parallax

1. is used for stars less than 100 light-years (LY) away 2. uses geometry to calculate distance 3. is the apparent change in the position of a star in the night sky due to Earth's changing position as Earth

revolves around sun B. Star Brightness

1. Used for stars greater than 100 LY away 2. Complicated formula involves star's apparent and absolute magnitudes

C. Red shift 1. Brightness and parallax won't work for stars greater than 7 million LY away and most stars more than 7 million

LY from Earth 2. Astronomers estimate distance based on amount of red shift

a. More red shift means greater distance b. Less red shift means smaller distance

3. Controversial method IV. NUCLEAR FUSION

A. Nuclear fusion is the combining of two atoms to produce one larger atom, causing the release of nuclear energy B. Inside a normal star, gravitational forces are strong enough to squeeze (fuse) two hydrogen (H) atoms together to form

one atom of helium (He) C. Every second, the Sun changes about 600 billion kilograms (Kg) of H into 595.8 billion Kg of He and releases energy

1. Missing 4.2 Kg of mass converted into energy (heat and light) 2. Some of the light that is produced is not visible (x-rays, ultraviolet, infrared, etc.)

V. THE LIFE OF STARS A. Birthplace

1. Dark, cool interstellar clouds of dust and hydrogen gas (nebula) 2. Gravity causes gas and dust to be pulled to center of cloud and cloud begins to heat up

B. Protostar 1. After a million years, temp. is high enough to emit light 2. Nuclear fusion of H atoms begins as protostar contracts 3. Fusion heat causes the protostar to expand, but gravity causes it to contract. When these two forces balance, a

main-sequence star is born. C. Main-sequence star

1. Star remains stable until H fuel is used up a. Hot stars use up their fuel quicker than cool stars b. Medium-sized stars, such as sun, remain stable for about 10 billion years

2. Large stars can "burn" other fuels and become a giant D. Red Giant/Supergiant Stage

1. Nuclear fusion stops in core of star 2. Core of star grows hotter as gravity squeezes core more tightly 3. Nuclear fusion in outer shell becomes more intense causing star to expand until balanced by gravity again 4. As star expands, surface cools (red color) 5. Core converts He to carbon (C) and so on 6. Once all fuels are used up star collapses into a tiny dense sphere

E. Burnout and Death 1. Death of Low-Mass Stars

a. Low-mass stars most stable, remaining in main-sequence for up to 100 billion years b. Low-mass stars aren't hot enough to "burn" He so they collapse to form white dwarf once H is used

up 2. Death of Medium-Mass (Sun-like) Stars

a. Medium-mass stars become red giants b. When all He is burned, medium-mass red giants expel their outer atmosphere, creating an expanding

spherical cloud of gas called a planetary (or ring) nebula c. The remaining core collapses into a white dwarf

3. Death of Massive Stars a. After becoming a red supergiant, the star consumes all of its nuclear fuel up to Fe, collapses, and

explodes as a supernova b. Neutron stars and black holes are remnants of supernovae

F. Remains of Dead Stars 1. All stars eventually become either a white dwarf, neutron star, or black hole 2. White dwarfs and neutron stars don't experience nuclear fusion.

a. They emit light because they are very hot. b. They eventually cool and become dim.

3. Massive stars sometimes collapse to form tiny, super-dense black holes a. Black holes are extremely hot but their gravity is so strong that not even heat or light can escape b. Material sucked into invisible black hole becomes very hot and emits x-rays allowing scientists to locate

them

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Page 7: Lesson 207: STARS AND STELLAR EVOLUTION 207 Stars.pdf · Define parallax and explain how astronomers use it to measure distances to stars. 3. Algol is a binary star system. Explain

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Page 9: Lesson 207: STARS AND STELLAR EVOLUTION 207 Stars.pdf · Define parallax and explain how astronomers use it to measure distances to stars. 3. Algol is a binary star system. Explain

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