# Ast HW help.

1. Jan 31, 2010

### Kiwithepike

Hey guys, im new here so i hope this is in the right place. I just need help with a problem.

Suppose the earth produced as much energy per kilogram each second as the sun does. what would be the total energy output of earth be? how would the absolute magnitudes compare between the sun and earth

2. Jan 31, 2010

### tiny-tim

Welcome to PF!

Hi Kiwithepike ! Welcome to PF!

Tell us what you think, and we'll comment.

How does absolute magnitude depend on total energy?

3. Jan 31, 2010

### Kiwithepike

Its the measure of the absolute magnitude of luminosity at 10pc.

4. Jan 31, 2010

### tiny-tim

ok, and how does that depend on total energy?

eg, if you double the energy, what does that do to the absolute magnitude?

5. Jan 31, 2010

### Kiwithepike

ok think I got it, so if mass(s)= 2.0E30kg L(s)= 3.8E26W, and Mass(E)= 6.0E24kg
then, L(s)/(s)= x/m(e) yields
1.42E21 W?

6. Jan 31, 2010

### Kiwithepike

it doubles as well

7. Jan 31, 2010

### tiny-tim

No, absolute magnitude is logarithmic … see http://en.wikipedia.org/wiki/Luminosity" [Broken] for details.

Last edited by a moderator: May 4, 2017
8. Jan 31, 2010

### Kiwithepike

so i think i finally got it after some much needed rest,
is this correct. M1-M2=2.5log(L1/L2) =>
4.8-M1=2.5log(3E-6) =>
4.8-M1=-13.8 =>
M1=18.6?

And thank you so much for the help and patience with me!