Question

What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us? It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age. It is the point in a star cluster beyond which main sequence stars are not found, and it tells us the cluster's distance. It is the faintest and coldest main sequence star in a cluster, and it tells us the cluster's age. It is the mass of the most massive star in the star cluster, and it tells us the cluster's size.

Answer 1

Explanation: The turnoff point for a star refers to the point on the Hertzsprung–Russell diagram where it leaves the main sequence after its main fuel is exhausted-the main sequence turnoff. HR diagrams for two open clusters, M67 and NGC 188, showing the main sequence turn-off at different ages.