The effective temperature, or black body temperature, of the Sun (5777 K) is the temperature a black body of the same size must have to yield the same total emissive power.

A 1903 Langley bolograph with an erroneous solar constant of 2.54 calories/minute/square centimeter.

Solar irradiance spectrum at top of atmosphere, on a linear scale and plotted against wavenumber.

Solar irradiance spectrum above atmosphere and at surface^{[what solar elevation?]}

As the temperature decreases, the peak of the black-body radiation curve moves to lower intensities and longer wavelengths. The black-body radiation graph is also compared with the classical model of Rayleigh and Jeans.

x axis is wave length in the unit of nm y axis is intensity of the astronomic object in an arbitrary unit. Temperature of earth was 290K for calculation