What Is the Luminosity Distance Relationship?

[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...

 

[SpaceTiger]

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?

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

 

[turbo]

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'm lost...

Here is a nice page that might be useful.

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

 

[SpaceTiger]

Here is a nice page that might be useful.

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

Ack! You'll confuse the poor OP. This problem can be done simply from knowing the scaling of brightness with distance.

 

[turbo]

Ack! You'll confuse the poor OP. This problem can be done simply from knowing the scaling of brightness with distance.

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.

 

[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].