Ideal object that is a perfect absorber of light and also a perfect emitter of light. A perfect black body will absorb all radiation that falls on it, and will emit radiation that has a continuous spectrum determined only by the temperature of the black body:
Where, T is the temperature (K), λ = Distance from one peak of a wave to the next. Wavelength is measured in units of distance. The wavelengths of visible light correspond to ~400-650 nm. Wavelength is an important way to characterize a wave. For light, the shorter the wavelength, the higher the energy of the light wave. (cm), c = Speed at which electromagnetic radiation propagates in a vacuum. Although referred to as the speed of light, this should be more properly called the 'speed of a massless particle’ as it is the speed at which all particles of zero mass (not only photons, but gravitons and massless neutrinos if, k = Boltzmann’s constant (1.37 x 10-18 erg/K), and h = Planck’s constant (6.626 x 10-27 erg sec).
Light is emitted by solid objects because they are composed of atoms and molecules which can emit and absorb light. They emit light because they are vibrating due to their heat content (thermal energy). The distribution of energy radiated against wavelength follows the Planck curve and, for a given temperature, there is a particular wavelength at which the maximum emission takes place specified by Wien’s Law. Stars and hot solid bodies are not perfect black bodies, but their radiation can be described in terms of black-body properties.