1. Mar 21, 2005

### scissors

My problem is that I have the numbers...but I don't have a formula.

"The sun's temp. is about 6000 K, it's radius 700000 km. How much power is it radiating? If there is no dissipation between here and the sun, how much of this hits the earth?"

Is this the P = c/4*U thing?

2. Mar 21, 2005

### Andrew Mason

I'm not sure what equation you are referring to. You have to use the Stephan-Boltzman law for blackbody radiation:

$$P/A = \sigma T^4$$

where P/A = Power/Area, $\sigma$ is Stephan's constant and T is the temp. in K.

Then work out the cross-sectional area of the earth and divide that by the area of the surface of a sphere centred at the sun and intersecting the earth.

AM

3. Mar 21, 2005

### Quarkycharm

In case you don't know - Stefan's constant is equal to 5.67x10^-8 Wm^-2K^-4

4. Mar 21, 2005

### scissors

Ah, I see. Thanks a lot guys!