The age of a cluster can be found by
A) observing its position in the sky with respect to the Sun.
B) measuring its speed of motion relative to the Sun.
C) carrying out a number count of the stars in the cluster.
D) determining the turnoff point on the main sequence of its H-R diagram.

Question

Quizplus · Accepted Answer

The most accurate way to determine the age of a cluster is by analyzing its H-R diagram and determining the turnoff point on the main sequence. The turnoff point is the location on the diagram where stars are leaving the main sequence and beginning to evolve into red giants. The age of the cluster can be calculated by comparing the turnoff point with theoretical models of stellar evolution. Observing its position in the sky, measuring its speed of motion, and carrying out a number count of the stars in the cluster can provide useful information, but not accurate enough to determine its age.

The Age of a Cluster Can Be Found by