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the H-R diagram of all the stars in a cluster of stars takes up a form, or curve, that is
“frozen” at the age of that cluster. The most massive stars have become giants and
even supergiants, while the least massive stars are still on the Main Sequence.
Clusters of different ages show different curves. So, a cluster’s curve in the H-R
diagram can be compared with curves produced theoretically from models of the
evolution of stars of different initial masses, until a reasonable match occurs for a
particular age of all the model stars. This is just one way that the comparison of one
star against another through spectral classification leads both to understanding stars
Fig. 1.6 Hertzsprung-Russell Diagram, based on 22,000 stars from the Hipparcos mission catalog
of 1000 stars from the Gliese catalog. (Source: https://upload.wikimedia.org/wikipedia/
commons/6/6b/HRDiagram.png)
1 An Introduction to Angelo Secchi and his Collegio Romano Observatory
the H-R diagram of all the stars in a cluster of stars takes up a form, or curve, that is
“frozen” at the age of that cluster. The most massive stars have become giants and
even supergiants, while the least massive stars are still on the Main Sequence.
Clusters of different ages show different curves. So, a cluster’s curve in the H-R
diagram can be compared with curves produced theoretically from models of the
evolution of stars of different initial masses, until a reasonable match occurs for a
particular age of all the model stars. This is just one way that the comparison of one
star against another through spectral classification leads both to understanding stars
Fig. 1.6 Hertzsprung-Russell Diagram, based on 22,000 stars from the Hipparcos mission catalog
of 1000 stars from the Gliese catalog. (Source: https://upload.wikimedia.org/wikipedia/
commons/6/6b/HRDiagram.png)
1 An Introduction to Angelo Secchi and his Collegio Romano Observatory