You observed three different star clusters and found that the main-sequence turnoff stars in Cluster 1 had spectral type F, the main-sequence turnoff stars in Cluster 2 had spectral type A, and the main-sequence turnoff stars in Cluster 3 had spectral type G. Which star cluster is the youngest and which one is the oldest?

Question

Quizplus · Accepted Answer

The spectral type of the main-sequence turnoff stars is related to their temperature and mass. Higher mass stars are hotter and have higher spectral types. Cluster 2 has main-sequence turnoff stars with spectral type A, which are the hottest and most massive stars among the three clusters. This means that Cluster 2 is the youngest of the three clusters. On the other hand, Cluster 3 has main-sequence turnoff stars with spectral type G, which are cooler and less massive than the stars in Cluster 2. This means that Cluster 3 is the oldest of the three clusters. Finally, Cluster 1 has main-sequence turnoff stars with spectral type F, which are intermediate in temperature and mass between the stars in Clusters 2 and 3. Therefore, Cluster 1 is intermediate in age between Clusters 2 and 3.

You Observed Three Different Star Clusters and Found That the Main-Sequence