Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 18, Problem 11Q
To determine
To Explain: The type of spectrum lines that would be observed when one looks at the spectrum of a reflection nebula.Theway, a spectrum demonstrates that the light was reflected fromnearby stars.
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As a star runs out of hydrogen to fuel nuclear fusion in its core, changes within the star usually cause it to leave the main sequence, expanding and cooling as it does so. Would a star with a radius 6 times that of the Sun, but a surface temperature 0.4 times that of the Sun, be more, or less luminous than the Sun?
Show and explain your reasoning.
You may assume the surface area of a sphere is A = 4πr2.
Tutorial
Star A has a temperature of 5,000 K. How much energy per second (in J/s/m2) does it radiate from a square meter of its surface?
If the temperature of Star A decreases by a factor of 2, the energy will decrease by a factor of
Star B has a temperature that is 5 times higher than Star A. How much more energy per second (compared to Star A) does it radiate from a square meter of its surface?
Part 1 of 4
The energy of a star is related to its temperature by
E = GT4
where σ = 5.67 x 10-8 J/s/m2/K4.
Part 2 of 4
To determine how much energy Star A is radiating, we just plug in the temperature to solve for EA.
EA =
J/s/m²
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Tutorial
Star A has a temperature of 6,000 K. How much energy per second (in J/s/m²) does it radiate onto a square meter of its surface?
If the temperature of Star A decreases by a factor of 2, the energy will decrease by a factor of
Star B has a temperature that is 5 times higher than Star A. How much more energy per second (compared to Star A) does it radiate onto a square meter of its surface?
Part 1 of 4
The energy of a star is related to its temperature by
E = OTA
where o = 5.67 x 10-8 J/s/m²/K4.
Part 2 of 4
To determine how much energy Star A is radiating, we just plug in the temperature to solve for EA.
EA
J/s/m²
Chapter 18 Solutions
Universe: Stars And Galaxies
Ch. 18 - Prob. 1QCh. 18 - Prob. 2QCh. 18 - Prob. 3QCh. 18 - Prob. 4QCh. 18 - Prob. 5QCh. 18 - Prob. 6QCh. 18 - Prob. 7QCh. 18 - Prob. 8QCh. 18 - Prob. 9QCh. 18 - Prob. 10Q
Ch. 18 - Prob. 11QCh. 18 - Prob. 12QCh. 18 - Prob. 13QCh. 18 - Prob. 14QCh. 18 - Prob. 15QCh. 18 - Prob. 16QCh. 18 - Prob. 17QCh. 18 - Prob. 18QCh. 18 - Prob. 19QCh. 18 - Prob. 20QCh. 18 - Prob. 21QCh. 18 - Prob. 22QCh. 18 - Prob. 23QCh. 18 - Prob. 24QCh. 18 - Prob. 25QCh. 18 - Prob. 26QCh. 18 - Prob. 27QCh. 18 - Prob. 28QCh. 18 - Prob. 29QCh. 18 - Prob. 30QCh. 18 - Prob. 31QCh. 18 - Prob. 32QCh. 18 - Prob. 33QCh. 18 - Prob. 34QCh. 18 - Prob. 35QCh. 18 - Prob. 36QCh. 18 - Prob. 37QCh. 18 - Prob. 38QCh. 18 - Prob. 39QCh. 18 - Prob. 40QCh. 18 - Prob. 41QCh. 18 - Prob. 42QCh. 18 - Prob. 43QCh. 18 - Prob. 44QCh. 18 - Prob. 45QCh. 18 - Prob. 46QCh. 18 - Prob. 47QCh. 18 - Prob. 48QCh. 18 - Prob. 49Q
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- Describe the spectrum of each of the following: A. starlight reflected by dust, B. a star behind invisible interstellar gas, and C. an emission nebula.arrow_forwardWhat causes reddening of starlight? Explain how the reddish color of the Sun’s disk at sunset is caused by the same process.arrow_forwardA star has a surface temperature of T = 10,000 K and a radius three times that of the Sun, R = 3R (recall that symbolizes the Sun). What is its luminosity, L, in units of solar luminosities, L ? Give your answer to three significant figures. answer, expressed in solar luminosities, tells how many times more luminous this star is than the Sun.arrow_forward
- 1 Solar constant, Sun, and the 10 pc distance! The luminosity of Sun is + 4- 1026 W - 4- 1033ergs-1, The Sun is located at a distance of m from the Earth. The Earth receives a radiant flux (above its atmosphere) of F = 1365W m- 2, also known as the solar constant. What would have been the Solar contact if the Sun was at a distance of 10 pc ? 1AU 1 1.5-+ 1011arrow_forwardExplain why the sky is blue and how that relates to reflection nebulae.arrow_forward12. A star with spectral type MO has a surface temperature of 3750 K and a radius of 0.63 Rsun: How many times more luminous is this star than the Sun? (if it is less luminous enter a number less than one) Answer: Submit All Answers Last Answer: 0.0923 Incorrect, tries 1/5. Hint: Use the Luminosity equation, which says that L is proportional to R^2 T^4. If you keep these as ratios compared to the sun, your L will also come out as a ratio compared to the Sun. This star has a mass of 0.4 Msun- Using the simple approximation that we made in class, what is the main sequence lifetime of this star? You may assume that the lifetime of the sun is 1010 yr. Answer: Submit All Answers Compare this to the lifetime of a MO star listed in Table 22.1 (computed using a more sophisticated approach). Is the value you calculated in the previous problem longer or shorter than what is reported in the table? (L for longer, S for shorter) (You only get one try at this problem.) Answer: Submit All Answersarrow_forward
- If the hottest star in the Carina Nebula has a surface temperature of 51,000 K, at what wavelength (in nm) does it radiate the most energy? Hint: Use Wien's law: ?max = 2.90 ✕ 106 nm · K T How does that compare with 91.2 nm, the wavelength of photons with just enough energy to ionize hydrogen? -The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen. -The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen. -The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen. -The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen.arrow_forwardChoose the correct statements concerning spectral classes of stars. (Give ALL correct answers, i.e., B, AC, BCD...) A) Neutral hydrogen lines dominate the spectrum for stars with temperatures around 10,000 K because a lot of the hydrogen is in the n=2 level. B) Hydrogen lines are weak in type O-stars because most of it is completely ionized. C) Oh Be A Fine Guy/Girl Kiss Me, is a mnemonic for remembering spectral classes. D) The spectral sequence has recently been expanded to include L, T, and Y classes. E) K-stars are dominated by lines from ionized helium because they are so hot. F) The spectral types of stars arise primarily as a result of differences in temperature.arrow_forwardTutorial Star A has a temperature of 5,000 K and Star B has a temperature of 6,000 K. At what wavelengths (in nm) will each of these star's intensity be at its maximum? If the temperatures of the stars increase, the wavelength of maximum intensity. What is the temperature (in K) of a star that appears most intense at a wavelength of 829 nm? Part 1 of 4 Wien's Law tells us how the temperature of a star determines the wavelength of maximum intensity or at what wavelength the star appears brightest. 2.90 x 106 TK If the temperature is in kelvin (K) then A is in nanometers (nm). Anm ^A = AB = = Part 2 of 4 To determine the wavelengths of maximum intensity for the two stars: 2.90 x 106 2.90 x 106 K nm nmarrow_forward
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