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Physics 1060 - Fall 2003
Dr. Mike Fanelli
Hints for Assigned Problems
Problems are taken from Chaisson and McMillan, fourth edition.
CHAPTER 17
PROBLEM 4:
A star is determined to have a surface temperature twice that of the Sun, and a
luminosity 64X greater. What is this star’s radius, expressed in solar units ?
HINT: Problem 4 is an application of the radius – luminosity – temperature relation for
stars. Given two of these values, the third is found using that relation, described on pg
449 in the text.
PROBLEM 10:
Given a star with an apparent magnitude of 10.0, and an absolute magnitude of 2.5, you
are asked to find the distance to the star.
HINT: A star appears fainter if it is located further away, just like any luminous object.
The magnitude of a star represents its brightness, either its perceived brightness, known
as its apparent magnitude, or its actual, true, brightness, known as its absolute magnitude.
More luminous stars have smaller magnitudes, an unusual attribute of the magnitude
system. The star here appears relatively faint, at 10th magnitude. It must be further than
10 parsecs, since absolute magnitudes are defined as the magnitude a star would have if
located at 10 parsecs from Earth. The quoted absolute magnitude is 2.5, a much brighter
value, than the observed one. Use the formula in MP 17-1, to determine the distance in
parsecs to this star.
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