Concept explainers
(a)
The distance of the distant star.
(a)

Answer to Problem 38QAP
The distance of the distant star is
Explanation of Solution
Write expression for distance of delta star.
Here,
Write expression for luminosity of delta star.
Here,
Write expression for luminosity of distant star.
Here,
Write expression for apparent brightness of delta star.
Here,
Write expression for apparent brightness of distant star.
Here,
Rearrange above expression for
Conclusion:
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Thus, the distance of the distant star is
(b)
The distance of more distant Cepheid variable is measurable by parallax.
(b)

Answer to Problem 38QAP
The distance of more distant star cannot be measured by parallax method.
Explanation of Solution
To measure the distance of any astronomical object requires a very large baseline and highly precise angular measurements. Due to revolution of Earth around Sun, the direction of a nearby stars changes from Earth. Nearby stars appear to move back and forth relative to more distant stars and the motion known as stellar parallax.
Cepheids have very high luminosities, they are variable stars in which the period of variability is directly related to the luminosity. As they have very high luminosity they are easy to detect and only period of variability is required to find the true luminosities. From the apparent brightness of the Cepheid, the distance can easily be calculated.
The distance of distant star is more than
Conclusion:
Thus, the distance of more distant star cannot be measured by parallax method.
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Chapter 13 Solutions
EBK UNDERSTANDING OUR UNIVERSE (THIRD E
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