# How to estimate star's mass without gravitation constant?

1. Dec 10, 2004

### smm

hi! title tells all

2. Dec 10, 2004

### orange

Hey!

If it is a main sequence star, you can tell what spectral class it belongs to by looking at its color. Every class has certain features, among them mass.

3. Dec 10, 2004

### franznietzsche

Using absolute luminosity, and the surface temperature(represented by spectral class), you could calculate the total Mass.

4. Dec 10, 2004

### Nereid

Staff Emeritus
Welcome to Physics Forums smm! (and a belated welcome to orange as well).

I'm not sure I understand smm's question ... no matter how you arrive at an estimate of the mass of a star, somewhere in the chain of observation and logic, you will use G.

For example, if you estimate its mass from its absolute luminosity, you are relying indirectly on G, because theories which lead to an understanding of the mass-luminosity relationship have gravity (and hence G) as a key element. Similarly, if you use a mass-luminosity relationship as a purely observational device (i.e. you've observed enough stars to plot the relationship, even if you have no idea of why it should be like that), you'll find that observations which established the mass of stars in your empirical relationship depended on G.

Perhaps you could clarify your question a bit for us please smm?