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A hydrogen atom with proton and electron spins aligned (top) undergoes a flip of the electron spin, resulting in emission of a photon with a 21 cm wavelength (bottom) The hydrogen line, 21 centimeter line, or H I line [a] is a spectral line that is created by a change in the energy state of solitary, electrically neutral hydrogen atoms.
Some of the more notable frequency bands used by radio telescopes include: Every frequency in the United States National Radio Quiet Zone; Channel 37: 608 to 614 MHz; The "Hydrogen line", also known as the "21 centimeter line": 1,420.40575177 MHz, used by many radio telescopes including The Big Ear in its discovery of the Wow! signal
Lines are named sequentially starting from the longest wavelength/lowest frequency of the series, using Greek letters within each series. For example, the 2 → 1 line is called "Lyman-alpha" (Ly-α), while the 7 → 3 line is called "Paschen-delta" (Pa-δ). Energy level diagram of electrons in hydrogen atom
In principle, any emission line can be used to make intensity maps if it can be detected. Other emission lines that have been proposed as cosmological tracers include: Rotational transitions in molecules, such as carbon monoxide [13] Fine structure transitions from species such as ionized carbon [14] Lyman-alpha emission from hydrogen [15]
The "visible" hydrogen emission spectrum lines in the Balmer series. H-alpha is the red line at the right. Four lines (counting from the right) are formally in the visible range. Lines five and six can be seen with the naked eye, but are considered to be ultraviolet as they have wavelengths less than 400 nm.
Lyman-alpha, typically denoted by Ly-α, is a spectral line of hydrogen (or, more generally, of any one-electron atom) in the Lyman series.It is emitted when the atomic electron transitions from an n = 2 orbital to the ground state (n = 1), where n is the principal quantum number.
The spectrum appears in a series of lines called the line spectrum. This line spectrum is called an atomic spectrum when it originates from an atom in elemental form. Each element has a different atomic spectrum. The production of line spectra by the atoms of an element indicate that an atom can radiate only a certain amount of energy.
Electromagnetic – the hyperfine transition of hydrogen, also known as the hydrogen line or 21 cm line 2.4 GHz: Electromagnetic – microwave ovens, wireless LANs and cordless phones (starting in 1998) 2.6–3.8 GHz: A common desktop CPU speed as of 2014 5.8 GHz: Electromagnetic – cordless telephone frequency introduced in 2003 10 10: 10 GHz