# Figuring out mass of a star based on diameter

1. Oct 4, 2008

### NOBARTHOLEM

How do you find the mass of a star based on its diameter? are there other factors that play into it and other things like that or is it just an equation???

2. Oct 4, 2008

### Janus

Staff Emeritus
For main sequence stars you can use

$$R=M^{.8}$$

with R being the diameter. For non-main sequence stars, this doesn't hold however. For instance, when our Sun expands into a red giant, its mass will not increase but its radius will do so greatly. Another Example is Betelgeuse, a super giant with a mass 14 times that of the Sun and a radius 630 times as much.

3. Oct 5, 2008

### NOBARTHOLEM

i can figure out that non main sequence stars hold the same mass because its just less matter per square mile or sqaure yoctometer or whatever measure u want to use.

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