| Astrophysics (Index) | About |
The electromagnetic spectrum is the range of wavelengths and frequencies of electromagnetic radiation (EMR). Everyday use of the word spectrum refers to the range of wavelengths of visible light, which is one type of EMR, the rest of EMR covering a spectrum spanning any wavelength:
| EMR type (i.e., band) | wavelengths | frequencies | photon energies |
| subradio | >100000km | 0-3Hz | 0-12×10-15eV |
| radio | 1mm-100000km | 3Hz-300GHz | 12x10-15eV-1.3meV |
| infrared | 750nm-1mm | 300GHz-400THz | 1.3meV-1.8eV |
| visible light | 400-750nm | 400-750THz | 1.8-3.1eV |
| ultraviolet | 10-400nm | 750THz-30PHz | 3.1-124eV |
| X-rays | 0.01-10nm | 30PHz-30EHz | 124eV-124keV |
| gamma rays | 0-0.1nm | >30EHz | >124keV |
(Some EMR phenomena are best explained characterizing EMR as a stream of particles termed photons, each carrying an amount of energy proportional to the EMR frequency.) Of note is that visible light occupies a much smaller portion of this spectrum than these other bands. Exact thresholds specifying these bands are not agreed upon, but the above thresholds are representative and cited thresholds are generally not far from these. The terms X-ray and gamma ray were coined for radiation from two distinct types of source rather than based upon a wavelength threshold, but distinction using a threshold is common in astronomy. The term microwave is used for the short-wavelength end of the radio spectrum and the term submillimeter for the long-wavelength end of infrared. The term millimeter is used for the wavelength range of roughly a millimeter, spanning the threshold.
For more detail, see Wavelengths Table.