General astronomy

General astronomy

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General astronomy

atmospheric dispersion corrector

Astronomy; General astronomy

An optical device usually comprising two thin prisms which can rotate to compensate for the elongation of a star image caused by the wavelength dependence of the refractive index of air.

atmospheric extinction

Astronomy; General astronomy

Decrease in the intensity of light from a celestial body due to absorption and scattering by the Earth's atmosphere. The extinction increases from the zenith to the horizon and affects short ...

atomic mass constant (mu)

Astronomy; General astronomy

One-twelfth the mean mass of an atom of carbon 12 (including the orbital electrons.)

atomic mass number

Astronomy; General 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.

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 ...

azimuth

Astronomy; General astronomy

1) Angular distance from the north point eastward to the intersection of the celestial horizon with the vertical circle passing through the object and the zenith. 2) Directional bearing around the ...