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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where the mass of the hydrogen atom was unity, later they were based on oxygen or oxygen 16; these scales have all been replaced by the carbon 12 scale.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
a general concept formed by extracting common features from specific examples
Industry:Astronomy
Peculiar star whose metallic lines are as strong as those of the F stars but whose hydrogen lines are so strong as to require that they be classed with the A stars. They are generally short-period (<300d) spectroscopic binaries with high atmospheric turbulence and variable spectra, and are slower rotators than normal A stars.
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
1) A spiral galaxy (kS5 in Morgan's classification) in the Local Group, about 650-700 kpc distant (MV = -21), visible to the naked eye as a fuzzy patch in the constellation of Andromeda. Total mass about 3.1 × 1011 Msun ; i = 77? heliocentric velocity - 180 km s-1. Its nucleus exhibits noncircular gas motions. It is similar to but slightly larger than our Galaxy.
2) Major spiral galaxy, 2.2 million light-years from Earth. Gravitationally bound to the Milky Way with which it shares membership in the Local Group, it is currently approaching us, rather than receding as is the case for most galaxies.
3) The largest galaxy in the Local Group. Also known as the Great Spiral and M31. It is about one and a half times the size of our own galaxy, and contains at least 300 globular clusters. Two smaller, elliptical galaxies (M32 and NGC 205) lie close to it.
4) The largest member of the local group. It is a giant spiral galaxy that lies 2.4 million light-years away.
Industry:Astronomy
