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One-twelfth the mean mass of an atom of carbon 12 (including the orbital electrons.)
Industry:Astronomy
The total number of protons and neutrons in an atom's nucleus. For example, oxygen-16 has a mass number of sixteen, because it has eight protons and eight neutrons.
Industry:Astronomy
The masses of atoms and molecules are generally given in atomic mass units. These units are based on a scale in which the mass of carbon 12 is taken to be 12. Atomic masses were originally given as atomic weights on a scale where the mass of the hydrogen atom was unity, later they were based on oxygen or oxygen 16; these scales have all been replaced by the carbon 12 scale.
Industry:Astronomy
The number of protons in an atom's nucleus. This determines the type of element.
Industry:Astronomy
The falling off of the energy density of radiation with distance from the source, or with passage through an absorbing or scattering medium.
Industry:Astronomy
the light produced by excited atoms and ions in the upper atmosphere of a planet
Industry:Astronomy
A phenomenon occurring when a discrete double-excitation state of an atom lies in the ground-state continuum. In the autoionization process one of the excited electrons is ejected, leaving the ion in an excited state (see dielectronic recombination; see also Auger effect). (also called pre-ionization.)
Industry:Astronomy
A hypothetical spin-0 particle with a very small mass of 10-5-10-3 eV. It was postulated in order to provide a natural solution to the "strong CP problem".
Industry:Astronomy
