# How do we determinate the mass of stars

1. Sep 10, 2009

### Bjarne

How do we determinate the mass of stars (or planet) in other solar systems?

2. Sep 10, 2009

### Arch2008

Last edited by a moderator: May 4, 2017
3. Sep 13, 2009

### smallphi

The mass of a planet or a star can be infered by observing a body orbiting around it - you have to measure the orbital period (time) and the dimensions of the orbit (radius for circles, semimajor axis for ellipse) and then use Newton's law for gravitation to calculate the gravitating mass. The astronomy textbook example is calculating the masses of two stars that orbit around their common center of mass - the so called binary stars. We know the gravitating mass of the Sun from the periods and distances to its planets.

I think mass of star can be infered from it's spectrum by modelling the processes inside it but that is model dependent, let astronomers say how much its reliable.

Last edited: Sep 13, 2009
4. Sep 14, 2009

### Chronos

Interfereometry is the usual measurement method.

5. Sep 14, 2009

### qraal

For size, not mass.

6. Sep 15, 2009

### Chronos

7. Sep 15, 2009

### Arch2008

Luminosity measurements using interferometry may be mainstream, however the mass is determined using the mass-luminosity relation (MLR), as your link notes.

8. Sep 16, 2009

### Chronos

Agreed, I dont see the issue here.