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Radio astronomy studies radiation with wavelengths greater than approximately one millimeter.[38] Radio astronomy is different from most other forms of observational astronomy in that the observed radio waves can be treated as waves rather than as discrete photons. Hence, it is relatively easier to measure both the amplitude and phase of radio waves, whereas this is not as easily done at shorter wavelengths.[38] Although some radio waves are produced by astronomical objects in the form of thermal emission, most of the radio emission that is observed from Earth is the result of synchrotron radiation, which is produced when electrons orbit magnetic fields.[38] Additionally, a number of spectral lines produced by interstellar gas, notably the hydrogen spectral line at 21 cm, are observable at radio wavelengths.[9][38] A wide variety of objects are observable at radio wavelengths, including supernovae, interstellar gas, pulsars, and active galactic nuclei.[9][38] |
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