Download Stellar Evolution – Test Review Answers

Stellar Evolution – Test Review Answers
1.
2.
3.
4.
5.
6.
D
C
A
B
C
C
7.
8.
9.
10.
11.
12.
B
C
C
D
D
D
13.
14.
15.
16.
17.
18.
C
B
C
C
B
A
19.
20.
21.
22.
23.
24.
C
D
C
D
B
D
25. D
26. C
27. C
Part II – Short Answer:
1. Name four characteristics astronomers use to classify stars.
Composition, color, temperature, brightness, size.
2. The full array of all types of electromagnetic radiation is called the electromagnetic spectrum. What are the
names of the longest-wavelength waves and the shortest-wavelength waves?
Electromagnetic radiation extends from the longest-wavelength radio waves to the shortest-wavelength
gamma rays.
3. What is a spectrograph and what do astronomers use them for?
Astronomers use spectrographs to determine the elements found in stars. A spectrograph is a device that
breaks light into colors and produces an image of the resulting spectrum. The light from nearby planets,
distant stars, and remote galaxies has characteristic spectra that reveal the chemical composition of these
celestial objects.
4. Describe a continuous spectrum.
A continuous spectrum is a complete rainbow of colors without any spectral lines.
5. Describe an emission line spectrum.
An emission line spectrum is a series of bright spectral lines against a dark background. Each chemical
element produces its own unique pattern of spectral lines.
6. Describe an absorption line spectrum.
An absorption line spectrum is a series of dark spectral lines among the colors of the continuous spectrum.
The dark lines in the absorption spectrum of a particular gas occur at exactly the same wavelengths as the
bright lines in the emission spectrum of that same gas.
7. Why do astronomers see an absorption spectrum when they take spectra of stars?
The light that moves outward through the sun is a continuous spectrum since the interior regions of the sun
have high density. However, when the light reaches the low density region of the solar atmosphere, some
colors of light are absorbed.
8. Why are brown dwarfs not considered true stars?
Unlike true stars, brown dwarfs are too small to sustain thermonuclear fusion.
9. Describe the relationship between the peak wavelength of light, color, and temperature of stars.
The intensity of light from a relatively cool star peaks at long wavelengths, making the star look red. A hot
star’s intensity curve peaks at shorter wavelengths so the star looks blue. Red stars are relatively cold, with
low surface temperatures; blue stars are relatively hot, with high surface temperatures.
10. What is luminosity and what does it depend upon?
Luminosity is the total energy that a star produces in one second. It depends on both the radius of the star
and on its surface temperature.
1.
11. What do astronomers use the H-R diagram for?
Astronomers use the H-R diagram to classify stars and to understand how stars change over time.
12. What percentage of stars are main-sequence stars?
90 percent.
13. Describe the relationship between luminosity and surface temperature of main-sequence stars.
In the main sequence, luminosity increases as surface temperature increases.
14. Where are the cooler, dimmer stars found on the H-R diagram?
Lower right.
15. Where are the hotter, more luminous stars found on the H-R diagram?
Upper left.
16. Where is the Sun located on the H-R diagram?
Nearly in the middle of both the temperature and luminosity scales relative to other stars. This puts it around
the middle of the main sequence.
17. Where are giant stars, supergiant stars and white dwarfs found on the H-R diagram, relative to the main
sequence?
Giant and supergiant stars lie above the main sequence, while white dwarfs are below the main sequence.
18. What is the relationship between mass, luminosity, size, and surface temperature for main-sequence stars?
The greater the mass of a main-sequence star, the greater its luminosity (and also the greater its radius and
surface temperature). In other words, stars that are higher up (brighter) on the main sequence are more
massive, larger, and hotter.
19. Describe the beginning of a star’s life.
The birth of a star begins when a disturbance, such as the shockwave from a supernova, triggers part of a
nebula to collapse inward. Gravity can then pull some of the gas and dust in the nebula together. The
contracting cloud is then called a protostar. A protostar is the earliest stage of a star’s life.
20. At what point does the protostar become a main-sequence star?
Once the outward pressure created by the energy given off during nuclear fusion balances the inward
gravitational collapse of material.
21. Describe the relationship between the lifetime of a star and its mass.
Small-mass stars use their fuel more slowly than large-mass stars, so they have much longer lives.
22. List the stages in the life of a low-mass star.
Nebula, protostar, main-sequence star, red giant, white dwarf, black dwarf.
23. List the stages in the life of a high-mass star.
Nebula, protostar, main-sequence star, supergiant, supernova, neutron star or black hole.
2.