When the stars of the following open clusters are plotted on an H-R diagram, the temperature values for the turning points are approximately: Coma (10,000 K), h + $\chi$ (40,000 K), M67 (7500 K), and Pleiades (20,000 K). Which cluster is oldest?
A)Coma
B)h + $\chi$
C)M67
D)Pleiades

Question

Quizplus · Accepted Answer

The main sequence turnoff point on an H-R diagram is a good indicator of the age of a star cluster. The cooler the turnoff point, the older the cluster. M67 has the lowest temperature turnoff point, indicating that it is the oldest cluster.

When the Stars of the Following Open Clusters Are Plotted χ\chiχ

When the Stars of the Following Open Clusters Are Plotted $\chi$