Using the technique of main- sequence fitting to determine the distance to a star cluster requires that .
A)we use ultraviolet and X- ray telescopes
B)we have telescopes powerful enough to allow us to identify the spectral types of main- sequence stars of many masses in the cluster
C)the cluster be near enough for us to measure the parallax of its stars
D)we have a well- calibrated period- luminosity relation for Cepheid variable stars

Question

Quizplus · Accepted Answer

Main-sequence fitting involves identifying main-sequence stars of different spectral types in the star cluster and comparing their apparent magnitudes to their known absolute magnitudes. This requires telescopes powerful enough to identify spectral types of main-sequence stars. Options A and D are irrelevant to main-sequence fitting, and option C is necessary to measure the distance using parallax, but it is not the method used for main-sequence fitting.

Using the Technique of Main- Sequence Fitting to Determine the Distance