What is used observationally to determine the age of a star cluster?

Answer 1

You cannot determine the age of a star based on it's luminosity or spectral class.

However, you can make *assumptions*.

OB and A stars are massive and will have a short lifespan in the millions of years.
FG and K stars have a longer life period - in the billions of years.
KMWLY and T stars are stars those that cause problems.

Most stars in this class are red dwarfs, stars that are so low in mass that they have a low rate of nuclear fusion and last for tens of billions of years.

In general - and I mean in general - a redder shift, should indicate an older star but you cannot use the HR- Diagram to determine this.

Answer 2

Astronomers estimate the mass of stars at the "main-sequence turnoff" on the HR diagram.

Observationally, they use the luminosities and colors of the stars. Then they can plot the stars on the HR diagram.

For more details, use the "related links" below.

Answer 3

In some cases, we can analyze the spectrum of the star and figure out the ratio of helium to hydrogen. Since a star fuses hydrogen and produces helium as sort of a "nuclear ash", we can come up with a fairly good approximation of how old the star is.

Answer 4

You can estimate the age of a star cluster by noting the turnoff point in the distribution of data points that represent it's stars in the H-R diagram.

Answer 5

The main sequence turnoff