Astronomy
Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Chapter 28, Problem 19E

Using the information from Example 28.1, how much fainter an object will you have to be able to measure in order to include the same kinds of galaxies in your second survey? Remember that the brightness of an object varies as the inverse square of the distance.

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An observational survey of distant galaxies is undertaken that involves measuring their distances using cepheid variables and red-shifts using spectroscopy. Explain how cepheid variables can be used to measure the distances to galaxies. A spectral line is observed whose wavelength in the laboratory is de length of this spectral line observed in each galaxy, Xo, is listed in the table, along with the distance, d, to the galaxy. Determine the red-shift and the recession velocity of each galaxy and tabulate your results by making a copy of the table and filling in the blank spaces. Sketch a Hubble diagram using your results and determine the value of the Hubble constant Ho in units of km s-1 Mpc. 650 nm. The wave- Galaxy 1 652.69 Galaxy 2 Galaxy 3 Galaxy 4 Galaxy 5 653.01 do (nm) d (Mpc) 658.54 662.18 681.63 17 19 54 77 200 v (km s-1)
How astronomers determine the distance of a galaxy? Explain.
The surface brightness profiles of elliptical galaxies follow the Sersic formula with n = 4.  How much fainter is the elliptical galaxy at a radius of r compared r0 (the radius at which the brightness falls off by a factor of e), or in other words, what is the ratio of I(r)/I0.   Values: r = 14 r0

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