A continuous spectrum contains energy at all wavelengths, while a discrete spectrum only exists at certain wavelengths. Spectra are used to gather information about objects and materials. Emissions measurements can be represented with colors or graphs, and light or dark lines can indicate the presence or absence of radiation. The spectrum of a star passing through a gas cloud can show an absorption or emission spectrum. Incandescent light bulbs have a continuous spectrum, while neon signs produce a discrete spectrum.
A continuous spectrum includes energy at all wavelengths. This differs from a discrete spectrum, where radiation does not exist at all wavelengths, but only at certain wavelengths. Spectra are a topic of interest to astronomers, chemists, and others who gather information about the composition of objects and materials by studying their spectral profiles. An example of a continuous spectrum familiar to many laymen is the visible spectrum, the array of wavelengths of light visible to the human eye.
When viewing an emissions measurement from a continuous spectrum, a researcher can see the emissions and their concentrations at different points. In the case of visible light, this can be represented with a series of colors. Other types of radiation must be represented with colored graphs and charts because the radiation is not visible. You can gather information about an object by looking at the type of energy in its spectrum and plotting it along a curve.
In some cases, a reading will have light or dark lines, indicating the presence or absence of radiation emitted by the source. These show that the spectrum is discrete and energy of some wavelengths does not pass. This can occur for reasons such as obstacles between the source and the detector. When scientists expected a continuous spectrum, the appearance of lines may indicate an interesting phenomenon is occurring.
A classic example can occur when researchers look at the radiation spectrum of a star after it has passed through a cloud of gas. The gas absorbs energy at some wavelengths, creating an absorption spectrum or dark line. The researchers can also look at the spectrum of the gas itself and should see an emission or bright line spectrum, where the trapped energy is being released. When the spectra of the star and the gas are brought close to each other, the bright lines of the gas cloud should match the dark lines seen in the star’s spectrum reading. It is also possible that stars themselves generate emission or absorption spectra because they are surrounded by gas clouds that can interfere with the emission of radiation.
Incandescent light bulbs are an example of a continuous spectrum. When lit, they emit energy of all wavelengths within a specific range. Neon signs, on the other hand, produce discrete spectra with concentrations of red, blue, or other color light, which create a very distinctive visual appearance. The same property can be seen when the researchers heat samples of unknown gases and minerals, which can flare up when heated, creating ghostly emissions that betray their contents.
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