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Hydrogen-alpha, typically shortened to H-alpha or Hα, is a deep-red visible spectral line of the hydrogen atom with a wavelength of 656.28 nm in air and 656.46 nm in vacuum. It is the first spectral line in the Balmer series and is emitted when an electron falls from a hydrogen atom's third- to second-lowest energy level.
The red H-alpha spectral line of the Balmer series of atomic hydrogen, which is the transition from the shell n = 3 to the shell n = 2, is one of the conspicuous colours of the universe. It contributes a bright red line to the spectra of emission or ionisation nebula, like the Orion Nebula , which are often H II regions found in star forming ...
A violet hue can occur when the spectrum contains emission lines of atomic hydrogen. This may happen when the air contains high amount of water, e.g. with lightnings in low altitudes passing through rain thunderstorms. Water vapor and small water droplets ionize and dissociate easier than large droplets, therefore have higher impact on color.
The spectral series of hydrogen, on a logarithmic scale. The emission spectrum of atomic hydrogen has been divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to the electron making transitions between two energy levels in an atom.
Interstellar dust grains re-emit the energy they absorb from starlight as quasi-blackbody emission in the far infrared, corresponding to typical dust grain temperatures of 20–100 K. Very small grains, essentially fragments of graphene bonded to hydrogen atoms around their edges (polycyclic aromatic hydrocarbons, PAHs), emit numerous spectral ...
The nebula's color depends on its chemical composition and degree of ionization. Due to the prevalence of hydrogen in interstellar gas, and its relatively low energy of ionization, many emission nebulae appear red due to strong emissions of the Balmer series. If more energy is available, other elements will be ionized, and green and blue ...
Reflection nebula IRAS 10082-5647 observed by the Hubble Space Telescope. These interstellar clouds possess a velocity higher than can be explained by the rotation of the Milky Way . [ 5 ] By definition, these clouds must have a v lsr greater than 90 km s −1 , where v lsr is the local standard rest velocity.
Liquid water and ice emit radiation at a higher rate than water vapour (see graph above). Water at the top of the troposphere, particularly in liquid and solid states, cools as it emits net photons to space. Neighboring gas molecules other than water (e.g. nitrogen) are cooled by passing their heat kinetically to the water.