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 25, Problem 25Q
To determine
The cosmic background
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You record the spectrum of a distant star using a telescope on the ground on Earth. Upon
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The Andromeda Galaxy, M31, is the closest large spiral galaxy to our Milky Way. When we look at its chemical spectrum, we see that its hydrogen alpha emission line (Hα) has an observed wavelength of λobs = 655 nm.-Calculate z, being careful with the sign.-How fast is it moving in km/s?-Is it redshifted or blueshifted? Is it moving towards or away from us?
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Chapter 25 Solutions
Universe: Stars And Galaxies
Ch. 25 - Prob. 1QCh. 25 - Prob. 2QCh. 25 - Prob. 3QCh. 25 - Prob. 4QCh. 25 - Prob. 5QCh. 25 - Prob. 6QCh. 25 - Prob. 7QCh. 25 - Prob. 8QCh. 25 - Prob. 9QCh. 25 - Prob. 10Q
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- Would you expect to be able to detect an H II region in X-ray emission? Why or why not? (Hint: You might apply Wien’s law)arrow_forwardEven though neutral hydrogen is the most abundant element in interstellar matter, it was detected first with a radio telescope, not a visible light telescope. Explain why. (The explanation given in Analyzing Starlight for the fact that hydrogen lines are not strong in stars of all temperatures may be helpful.)arrow_forwardExplain how emission lines and absorption lines are formed. In what sorts of cosmic objects would you expect to see each?arrow_forward
- Why would we not expect to detect X-rays from a disk of matter about an ordinary star?arrow_forwardWhy is it difficult to determine where cosmic rays come from?arrow_forwardAt the low temperature found in some interstellar molecular clouds (around 100 K), molecular oxygen emission is strongest at a wavelength of 0.2521 cm. Determine the speed (in km/s) of a low temperature molecular cloud containing molecular oxygen if its strongest emission is at a wavelength of 0.1885 cm. Note that this cloud is moving towards us, so the answer should be negative.arrow_forward
- A)The star 58 Eridani is a feint but naked-eye star similar to the Sun. Suppose that you are observing this star in the night sky without a telescope. Ignoring any interstellar extinction or atmospheric absorption, approximately how many photons per second arrive at your retina? Show all steps in calculation . B) The Mid-infared Instrument (MIRI , camera and spectrograph ) on the James Webb Space Telescope operates in the band 5-28 µm . For 58 Eridani , approximatley how many photons per second can be used by this instrument ? Assume that MIRI takes all the photons from the full JWST mirror . Show all steps in calcultation . Describe breifly two or three other factors which play a role in determining the sensetivitu of an instrument such as MIRI ?arrow_forwardWhat is background radiation? Why is it important to determine the back-ground radiation for the effect of different distances?arrow_forwardAssuming stars to behave as black bodies stefan-boltzmann law to show that the luminosity of a star is related to its surface temperature and size in the following way: L = 4(3.14)R^2oT^4 where o= 5.67 ×10^-8 Wm^-2 K-4 is the stefan- boltzmann constant. Then use this expression together with the knowledge that the sun has a surface temperature of 5700k and radius 695 500km to calculate the luminosity of the Sun in units of Wattsarrow_forward
- Imagine that you are observing the light from a distant star that is located in a galaxy 100 million lightyears away from you. By analysis of the starlight received, you are able to tell that the image we see is of a 10- million-year-old star. You are also able to predict that the star will have a total lifetime of 50 million years, at which point it will end in a catastrophic supernova. a) How old does the star appear to be to us here on Earth now? b) How long will it be before we receive the light from the supernova event? c) Has the supernova already occurred? If so, when did it occur?arrow_forwardA planetary nebula is visible due to ____.a. blackbody continuum radiation from the interstellar mediumb. line emission from the interstellar mediumc. scattering from dust grains ejected by a dying stard. blackbody continuum radiation from a hot gas ejected by a dying stare. line emission from ionized hydrogen gas ejected by a dying star My guess is E. Please help me understand why I am wrong if so.arrow_forwardThe sun is a source of energy across the full spectrum, and its electromagnetic radiation bombards our atmosphere constantly. However, the Earth's atmospheric layers protect us from such high energy exposure. What do you think would happen if one day, these protective layers have all been destructed fully? How would the life on Earth be affected of this profoundly serious matter? Explain your answer in 3-5 sentences.arrow_forward
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