Black body radiation 

Black bodies emit a particular continuous spectrum. The plot below shows intensity versus wavelength. The curve can be scaled vertically for intensity to represent a source of any size, and horizontally for wavelength to represent a source at any temperature.

The peak for sunlight is in the visible (obviously). There is a 'cut off' in the UV and a long upper tail in the infrared. The peak wavelength is given by a simple formula known as Wein's law.

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