An Etymological Dictionary of Astronomy and Astrophysics

A person who questions the validity or authenticity of something purporting to be factual.

Etymology (EN): From M.Fr. sceptique and directly from L. scepticus “the sect of Skeptics,” from Gk. skeptikos “thoughtful, inquiring” (plural Skeptikoi “the Skeptics, followers of Gk. philosopher Pyrrho,” who lived c. 360-270 B.C.). from skeptesthai “to reflect, look, view,” → spectrum.

Etymology (PE): Šakdâvar, šakmand, from šakk, → doubt, + -âr contraction od âvardan “to bring, to cause, to produce,” → cause, or -mand suffix of relation/possession.

1. Inclined to skepticism; having an attitude of doubt.
   

   2. Doubtful about a particular thing.

See also: → skeptic; → -al.

1. A doubting or questioning attitude or state of mind.
   

   2a) The ancient school of Pyrrho of Elis that stressed the uncertainty of our beliefs in order to oppose dogmatism.
   

   2b) The doctrine that absolute knowledge is impossible, either in a particular domain or in general.
   

   2c) A methodology based on an assumption of doubt with the aim of acquiring approximate or relative certainty.
   

   3. Doubt or disbelief of religious tenets (TheFreeDictionary.com).

See also: → skeptic; → -ism.

General: Having an oblique direction or position;
being in a slanted or unsymmetrical position.
Geometry: Two or more lines that are not parallel and do not intersect.
Statistics: Having → skewness.

Etymology (EN): From Old North French eskiuer “to shy away from, avoid,” O.Fr. eschiver (Fr. esquiver “to shirk, dodge”) “to eschew, keep away from;” related to shy.

Etymology (PE): Kažâl, from kaž “crooked, bent, being aside” (cf. Skt. kubja- “hump-backed, crooked,” Pali kujja- “bent,” L. gibbus “hump, hunch,” Lith. kupra “hump”)

• -âl, → -al.

A tensor that is the negative of its → transpose. For example, a second-order covariant tensor A_jk if its components satisfy the equality: A_jk = - A_kj.
Also called antisymmetric tensor.

Etymology (EN): → skew; → symmetric; → tensor.

Etymology (PE): Tânsor, → tensor; pâd-, → anti-; hamâmun, → symmetric.

A measure of the degree of asymmetry of a distribution. If the left tail (tail at small end of the distribution) is more pronounced that the right tail (tail at the large end of the distribution), the function is said to have → negative skewness. If the reverse is true, it has → positive skewness. If the two are equal, it has → zero skewness.

See also: Noun from → skew + → -ness.

1. The external protective membrane or covering of an animal’s body, or that surrounding the flesh of a fruit or vegetable.
   

2. The outer protective covering of a structure. → skin effect.

Etymology (EN): M.E., from O.N. skinn “animal hide;” cf. O.H.G. scinten, Ger. schinden “to flay, skin;” Ger. dialect schind “skin of a fruit,” Flemish schinde “bark;” from PIE *sken- “to cut off.”

Etymology (PE): Pust “skin;” Mid.Pers. pôst “skin;” O.Pers. pavastā- “thin clay envelope used to protect unbaked clay tablets;” Av. pastô-, in pastô.fraθanhəm “of the breadth of the skin;” Skt. pavásta- “cover,” Proto-Indo-Iranian *pauastā- “cloth.”

The tendency of an → alternating current to concentrate in the outer layer of a conductor, caused by the → self-induction of the → conductor and resulting in increased → resistance.

See also: → skin; → effect.

The area high above the ground, buildings, landscape, or horizon.
The heavens or firmament, appearing as a great arch or vault.

Etymology (EN): M.E. from O.N. sky “cloud;” cf. O.E. sceo, O.S. scio “cloud;” O.H.G. scuwo, O.N. skuggi “shadow;” Goth. skuggwa “mirror;” PIE base *(s)keu- “to cover, conceal.”

Etymology (PE): Âsmân “sky;” Mid.Pers. âsmân “sky, heaven;” O.Pers. asman- “heaven;” Av. asman- “stone, sling-stone; heaven;” cf. Skt. áśman- “stone, rock, thunderbolt;” Gk. akmon “heaven, meteor, anvil;” Akmon was the father of Ouranos (Uranus), god of sky; Lith. akmuo “stone;” Rus. kamen; PIE base *akmon- “stone, sky.”
The link between the “stone” and “sky” concepts indicates that the sky had once been conceived as a stone vault by prehistoric Indo-Europeans.

The emission of a part of the night sky that does not contain any detectable objects. Sky background results from
the combined radiation from faint, unresolved stars and other emitting astronomical objects. The mean brightness of night sky background measured at the → Cerro Tololo Inter-American Observatory (CTIO) for the period 1992 to 2006 are:
U = 22.12, B = 22.82, V = 21.79, R = 21.19, and I = 19.85 mag arcsec^-2 ( → rms ~ 0.2 mag arcsec^-2). See also → sky brightness.

See also: → sky; → background..

Atmospheric (→ airglow, → auroral emission, → artificial light) or extraterrestrial (→ scattered  → sunlight from Moon, scattered → starlight, → interplanetary dust)
foreground light that → interferes with → observations.

See also: → sky; → brightness.

The act or instance of removing the contribution of non-related, intervening foreground light to the object.

See also: → sky; → subtraction.

The observation and recording of large extents of the sky with a particular instrument using one or more wavelengths in the same spectral domain. → survey.

See also: → sky; → survey.

The illumination of the night sky in urban areas caused by wasted light shining upward scattered off dust, humidity, and air. Skyglow is a type of → light pollution that results
from light fixtures emitting a portion of their light directly upward into the sky. Light scattered in the atmosphere creates an orange-yellow glow above a city or town. Skyglow interferes with sensitive astronomical instruments designed to capture light from distant stars, nebulae, and galaxies. Skyglow can often be detected hundreds of kilometers away.

Etymology (EN): → sky; → glow.

Etymology (PE): Nur, → light; foruq, → glow; šahr, → city; âsmân, → sky.

Solar radiation which reaches the observer from the general sky. It is sunlight which has undergone multiple scattering events with the molecules of the Earth’s atmosphere (Rayleigh scattering) or with clouds or other aerosols in the atmosphere. High levels of skylight reduce the contrast of a shadow. Also known as diffuse skylight, diffuse sky radiation.

See also: → sky; → light.