An Etymological Dictionary of Astronomy and Astrophysics
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A colorless, odorless → hydrocarbon, C₂H₆, which occurs with → methane in natural gas.

From eth-, from → ethyl, + -ane a suffix used in names of hydrocarbons of the methane or paraffin series.

An → alcohol having molecular formula C₂H₅OH. It is a colorless inflammable liquid with a characteristic odor. Ethanol is produced by fermentation of sugar: C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂. It is the active constituent of alcoholic beverages. It is used as a fuel and as a solvent in the extraction of specific substances. It is also known as → ethyl alcohol. Ethanol in the → interstellar medium was first detected toward the → Sagittarius B2 molecular cloud at 82.265, 90.118, and 104.809 GHz (B. Zuckerman et al. 1975, ApJ 196, L99).

Short for → ethyl alcohol.

1) Physics: A hypothetical medium filling all space formerly postulated to account for the propagation of → electromagnetic radiation through space. In order to facilitate description and to provide a physical explanation of various phenomena involving action at a distance and electromagnetism, a medium had been postulated with mechanical properties adjusted to provide a consistent theory. In 1887 Michelson and Morley attempted to measure the motion of the Earth through the ether. No such motion was detected. The → Michelson-Morley experiment has been repeated under different conditions, but the hypothesis of a stationary ether through which the Earth moves is not verified.
2) The substance supposed by Aristotle to constitute stars and fill the outer space.
3) Chemistry: A family of organic compounds with the general formula R-O-R', where R and R' are hydrocarbon radicals. In particular diethyl ether, C₂H₅OC₂H₅, which is a volatile colorless liquid with a pleasant smell.

From L. æther "the upper air, pure air," from Gk. aither "upper air," from aithein "to burn, shine."

A hypothesis put forward to explain the null measurement of the → ether drift. According to this hypothesis, the Earth somehow drags the ether with it as our planet rotates on its axis and revolves around the Sun. However, the ether drag hypothesis contradicts results from several experiments, including the → aberration of starlight.

→ ether; → drag.

1) The hypothetical motion of the supposed → ether relative to the Earth. The → Michelson-Morley experiment found no ether drift. An analogy is given by a boat drifting in a fast-flowing river due to the river's current. With the same power, the speed would be slower when sailing across the stream. Moreover, in order to reach directly opposite the starting point, the boat would have to be headed somewhat upstream. See also the → ether drag.
2) The motion of the Earth relative to the → rest frame defined by the → cosmic microwave background radiation.

→ ether; → drift.

A combining form meaning "race, culture, people."

From Gk. ethnos "people, nation, class, tribe."

Qowm- loan from Ar. qaum "people, tribe, family."

The study of the beliefs, interpretations, and practices of specific cultures regarding celestial objects or phenomena. Ethnoastronomy uses the tools and methodologies of → ethnology in the study of astronomical conceptions.

→ ethno-; → astronomy.

The study of specific cultures (ethnic groups) in their different aspects (anthropological, social, cultural, etc.) to establish similarities and disparities between them.

→ ethno-; → logy.

A chemical group, C₂H₅, produced by removing a hydrogen atom from → ethane. For example, ethyl chloride is C₂H₅Cl

From Ger. Ethyl, from eth-, from → ether, + -yl a suffixed used in the names of radicals.

Same as → ethanol.

→ ethyl; → alcohol.

The study of the origins and history of the form and meaning of → words.

M.E., from L. etymologia, from Gk. etymologia, from etymon "true sense" (neuter of etymos) + logos, → -logy.

Riše-šenâsi, from rišé "root" (dialectal Tabari rexa; Kurd. regez, riše), from Mid.Pers. rêšak "root," maybe ultimately related to PIE *u(e)rad-, although the Skt. offshoot is absent (Gk. rhiza "root;" L. radix, radius "staff;" O.H.G. wurz "plant, herb;" Ger. Wurz; O.E. rot; E. root) + -šenâsi, → -logy.

A prefix meaning "good, well; true, genuine" (eupepsia; eukaryote); opposed to → dys-.

L. from Gk. eu "well," combining form of eus "good" (hu-gies "healthy"); cf. Mid.Pers. hu-; Av. hu- "good;" PIE base *su- "good," see below.

Mid.Pers. hu- "good, well" (hu-boy "sweet-smelling," hu-cihr "beautiful," hu-mânih "good-mindedness"); O.Pers. ^hu- "good, well" (ukāra- "having good people"); Av. hu-, hū- "well, good, beautiful" (hu-kərp- "well-shapen," hūxta- "well spoken," hu-manah- "good-minded"); Skt. su- "good" (svasti "well-being, good luck," sumánas- "good-minded," sūktá- "well spoken"); Gallic su-; O.S. su-; Welsh hy-; PIE base *su-, as above.

Of or pertaining to Euclid, or his postulates. → Euclidean division, → Euclidean geometry, → Euclidean space, → non-Euclidean geometry.

After the Gk. geometrician and educator at Alexandria, around 300 B.C., who applied the deductive principles of logic to geometry, thereby deriving statements from clearly defined axioms.

In arithmetic, the conventional process of division of two → integers. For a → real number a divided by b > 0, there exists a unique integer q and a real number r, 0 ≤ r <b, such that a = qb + r.

→ Euclidean; → division.

The geometry based on the postulates or descriptions of Euclid. One of the critical assumptions of the Euclidean geometry is given in his fifth postulate: through a point not on a line, one and only one line be drawn parallel to the given line. See also → non-Euclidean geometry.

→ Euclidean; → geometry.

A space in which the → distance between any two points is given by the → Pythagorean theorem: d² = (Δx)² + (Δy)² + (Δz)², where d is distance and Δx, Δy, and Δz are differential → Cartesian coordinates. Euclidean n-space Rⁿ is the set of all column vectors with n real entries.

→ Euclidean; → space.

→ spheres of Eudoxus.

→ spheres of Eudoxus.

Leonhard Euler (1707-1783), the eminent Swiss mathematician, physicist, and astronomer.

In → fluid mechanics, one of a set of → differential equations that govern the motion of a → compressible, → inviscid fluid. Euler equations correspond to the → Navier-Stokes equations with zero → viscosity.

→ Euler; → equation.

In any → triangle, the straight line on which always lie the → centroid, → circumcenter, and → orthocenter.

→ Euler; → line.