Spectroscopy is a complex art - but it can be very useful in helping scientists understand how an object like a black hole, neutron star, or active galaxy is producing light, how fast it is moving, and even of what elements it is made. A spectrum is simply a chart or a graph that shows the intensity of light being emitted over a range of eneriges. Spectra can be produced for any energy of light - from low-energy radio waves to very high-energy gamma-rays.
The Imagine the Universe! website hosted at NASA's Goddard Space Flight Center has a great tutorial about spectroscopy. The specific pages are linked below.
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Introduction to Spectroscopy |
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Making a spectrograph |
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What do spectra show us? |
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X-ray spectroscopy |