Hi all! I'm trying to build up a solar model, using real-world data where available, and filling in the weak low and high frequency extremes of the spectrum with a simple blackbody curve. All well and good. But when I apply Planck's law to the known data it goes awry! Here's what I'm working with. Effective radius of the sun's radiating surface: said to be about 7,00e8m Blackbody temperature of the sun: Said to be 5778 Earth distance to the sun: 149597870700m Calculated radial angle: 9,36e-3 (actual said to be 9,35 - so far, so good) Calculated steradians: 6,88e-5 (actual said to be 6,87e-5 - again, so far so good). Misc constants: Planck: 6,6260700400E-34 Speed of light: 299792458 Stefan-Boltzman: 1,3806485200E-23 ... that is, staying with SI units. Okay, now we get to planck's equation (in terms of wavelength). When I apply it first to short wavelengths - say, 280nm - I come up with 9,5045e12 W/m^2/sr (6,5377e-1 W/m^2/nm). Actual reported: http://rredc.nrel.gov/solar/spectra/am1.5/astmg173/ASTMG173.xls ... is said to be 8,2000e-2 W/m^2/nm. Okay, my value is significantly higher, but that's not necessarily a problem because the sun isn't a perfect blackbody, there's plenty of gaps. As I start going to longer wavelengths, the numbers start to converge toward a perfect blackbody, and then.... the real-world power figures *pass* the calculated figures! For example, at 495nm the real-world spectrum is 2,0510e0 W/m^2/nm, but I calculate that a perfect blackbody would emit 1,8135e0. Obviously the real-world should never be higher than the calculated! So something's wrong here. What do you think the problem might be?