# How Far nearby galaxy Problem

1. May 4, 2005

### bigman8424

A Cepheid variable in a nearby galaxy looks 10^6 times fainter than an identical Cepheid in the Milky Way. The Cepheid in the Milky Way is 1000 parsecs away. How far away is the nearby galaxy?

I know this formula
v = hd
but how does that help me?
i'm lost...

2. May 4, 2005

### SpaceTiger

Staff Emeritus
It doesn't. Did you learn a formula for the dependence of brightness (flux) on distance?

3. May 4, 2005

### turbo

Here is a nice page that might be useful.

http://staff.imsa.edu/science/astro/astrometry/rung4.html

4. May 4, 2005

### SpaceTiger

Staff Emeritus
5. May 4, 2005

### turbo

You're right, of course, but sometimes handing out the simplistic solution is not the best solution, like the old Chinese proverb:

Give a man a fish and he will eat for a day. Teach a man to fish, and he will spend his weekends drinking beer and his weekdays lying about the one that got away.

6. May 4, 2005

### Chronos

This is really a very simple exercise. You need only know the luminosity distance relationship... or you could do it the way SpaceTiger suggested... [which is the same thing].

Last edited: May 4, 2005