# Calculating distance to a star using magnitudes

1. Sep 26, 2016

### samjohnny

1. The problem statement, all variables and given/known data

2. Relevant equations
$m = m_0 − 2.5 log_{10} f$ where $m$ is the absolute magnitude of an object, and $m_0$ is the zero point.

3. The attempt at a solution

I'm having difficulty with is part b, the answer to which I believe is required for the subsequent parts.

I obtain the following through treatment of the given equation: $M_{abs}=m_{obs}-5log_5(\frac{d}{10})$ where $d$ is the distance we're looking to compute. Using the fact that both Star A and Vega are A0 stars, I assumed that the absolute V-band magnitude of Star A would be the same as Vega's, which would be $M_{abs}=+0.6$, however the observed/apparent magnitude $m_{obs}$ remains unknown, and so I'm unable to proceed to compute the distance.

It seems simple, but I can't quite put my finger on it..

2. Sep 27, 2016

### Staff: Mentor

You'll need the R-band magnitude of Vega I think. The question part about the colors indicates that you have to find some relation between R and V band.
Afterwards you can use the R band magnitude from (a).