The Austrian scientist Josef Stefan found there was a relationship between the amount of radiant energy emitted from a body and its temperature.
Radiation from the Sun.
The temperature of the surface of the sun is about 6000 °C. Sun spots (dark patches) are areas on the sun’s surface at a lower temperature due to variations in the sun’s magnetic field.
Solar constant (also called solar irradiance).
The Solar constant
The Solar constant is the amount of sunlight radiates from the sun and falls on earth. The measurement is per unit area and time but must be an average because we are closer to and further away from the sun at different times of the year, more here ...
the Black Can Vs Shiny Can