Continuous Spectra, Absorption Line Spectra, and Emission Line Spectra

This animation summarizes how different types of spectra are produced. A hot, glowing object such as a blackbody emits a continous spectrum of light. If this light passes through a cloud of cooler gas, the cloud selectively absorbs light of certain specific wavelengths. As a result of this absorption, the light from the hot blackbody that passes directly through the cloud is depleted in these wavelengths, and the spectrum of this light has dark absorption lines. The cloud does not retain all the light energy that it absorbs but radiates it outward in all directions. If the light radiated from the cloud of gas is viewed against a cold, dark background, its spectrum contains bright emission lines. The wavelengths of the dark absorption lines are the same as those of the bright emission lines. The chemical composition of the cloud determines the specific wavelengths that the cloud both absorbs and emits.