An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The absorption of → electromagnetic radiation in the → atmosphere mainly by → water vapor, → carbon dioxide, and oxygen. The atmosphere introduces two more limiting factors in → remote sensing: → atmospheric scattering and → atmospheric turbulence.

→ atmospheric; → absorption.

The large-scale movements of air around areas of high and low pressure whereby heat is distributed on the surface of the Earth. Atmospheric motion is driven by uneven heating of the planet. The atmosphere (and ocean) → transfers the excess heat from → tropics to → poles. The flow is determined by balance between → pressure gradients and the → Coriolis effect.

→ atmospheric; → circulation.

The splitting of starlight into a spectrum in the atmosphere because the atmosphere acts as a refracting prism. This phenomenon brings about a practical problem for spectroscopic observations using a slit. → differential refraction; → atmospheric refraction.

→ atmospheric; → dispersion.

The emission of electromagnetic radiation from the atmosphere due to thermal and → non-thermal processes. → Thermal emission comes mainly from → water vapor. Non-thermal processes result in emission lines oxygen (optical) and OH (near-IR). Atmospheric emission is a very significant source of noise in astronomical observations. See also → airglow, → aurora.

→ atmospheric; → emission.

The decrease in the intensity of light from a celestial body due to absorption and scattering by Earth's atmosphere. It increases from the zenith to the horizon and affects short wavelengths more than long wavelengths, so that objects near the horizon appear redder than they do at the zenith.

→ atmospheric; → extinction.

A → subatomic particle produced when → primary cosmic rays, impinge on the Earth's atmosphere producing a particle cascade, in which secondary particles decay into → muons. In the energy range up to 100 → GeV atmospheric muons come mostly from the decay of secondary → pions: π^±→ μ^± + anti-ν_μ. At higher energies, the → kaon contribution to the muon flux become significant, reaching the asymptotic value of 27% at about 10 TeV: K^±→ μ^± + anti-ν_μ.

→ atmospheric; → muon.

The shift in apparent direction of a celestial object caused by the bending of light while passing through the Earth's atmosphere. Since the density of the atmosphere decreases with altitude, the starlight will bend more as it continues down through the atmosphere. As a result, a star will appear higher in the sky than its true direction.

→ atmospheric; → refraction.

→ element diffusion.

→ atomic; → diffusion.

In → propositional logic, a → sentence without any → connectives. See also → molecular proposition.

→ atomic; → proposition.

A change in the → energy level or → state of an → atom in which a → quantum of energy is either gained or lost. See also → forbidden transition; → permitted transition; → semiforbidden transition.

→ atomic; → transition.

1) The act or faculty of attending, especially by directing the mind to an object.
2) Observant care; consideration (Dictionary.com).

→ attend; → -tion.

The falling off of the energy density of radiation with distance from the source, or with passage through an absorbing or scattering medium.

Verbal noun of → attenuate.

The fraction of a beam of → X-rays or → gamma rays that is absorbed or scattered per unit thickness of the → absorber. The linear attenuation coefficient, denoted by the symbol μ, appears in the equation I(x) = I₀e^-μx, where I(x) is the intensity at depth of x cm and I₀ is the original intensity.

→ attenuation; → coefficient.

The ratio of the radiation intensity after traversing a layer of matter to its intensity before.

→ attenuation; → factor.

The act or capability of attracting. A physical force (gravitational, electric, magnetic, etc.) exerted by material bodies.

Attraction, n. from → attract.

1) The act of attributing.
2) Something attributed.

Verbal noun of → attribute.

An electron that is emitted when an electron from a higher → energy level falls into a → vacancy in an inner shell, according to the → Auger-Meitner effect. The process usually occurs when the atom is bombarded with high energy electrons. If the collision ejects an inner-shell electron, an electron from a higher level will quickly drop to this lower level to fill the vacancy. Most of the time, the energy is released in the form of a photon. But sometimes the energy is transferred to another electron, which is ejected from the atom.

→ Auger-Meitner effect; → electron.

The → electromagnetic radiation emitted in planetary atmospheres involving the → aurora phenomenon.

→ auroral; → emission.

A roughly circular band around either geomagnetic pole above which there is a maximum of auroral activity. It lies about 10 to 15° of geomagnetic latitude from the geomagnetic poles.

→ auroral; → zone.

Computers: The process by which a user's identity is checked within the network to ensure that the user has access to the requested resources.

Verbal noun of → authenticate.