![]() ![]() the emission of the light by the source,. ![]() Whenever you are studying the light from an astronomical object, recall that there are three things you need to consider: Specifically, we will consider the Bohr model of the atom. In order to understand the origin of absorption and emission lines and the spectra that contain these lines, we need to first spend some time on atomic physics. That is, they were formulated on the basis of experiments. Like Kepler's laws of planetary motion, these are empirical laws. You can also summarize Kirchoff's laws in a diagram, like this one:Ĭredit: Penn State Astronomy & Astrophysics A low density, cool gas in front of a hotter source of a continuous spectrum creates a DARK LINE or ABSORPTION LINE spectrum.A low density, hot gas seen against a cooler background emits a BRIGHT LINE or EMISSION LINE spectrum.A luminous solid, liquid, or dense gas emits light of all wavelengths.The differences in these spectra and a description of how to create them were summarized in Kirchhoff’s three laws of spectroscopy: In the early days of spectroscopy, experiments revealed that there were three main types of spectra. Other astronomical sources (and also light sources you can test in a lab) are found to create spectra that show little intensity at most wavelengths but a few precise wavelengths where a lot of intensity is seen. These gaps in the spectrum where there is no light emitted are called absorption lines. If you look at the two spectra of stars, you see there are black bands in the image of the sun’s spectrum and areas in the plot where the intensity goes to zero or nearly zero in the spectrum of the blue straggler. Recall that blackbody radiation is continuous with no breaks. For example, consider the two spectra you looked at on a previous page: the sun and a blue straggler star. In reality, few objects emit exactly a blackbody spectrum. However, I have stressed a few times that blackbody radiation is only emitted by an “ideal” or “perfect” radiator. Studying blackbody radiation is a useful exercise. ![]()
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