# Ast HW help.

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

tiny-tim
Homework Helper
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?

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

tiny-tim
Homework Helper
ok, and how does that depend on total energy?

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

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?

it doubles as well

tiny-tim
Homework Helper
it doubles as well

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

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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!