An Etymological Dictionary of Astronomy and Astrophysics
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A hypothetical structure built around a → star by an advanced → civilization to utilize most or all of the → energy radiated by their star. The idea of such a sphere was first formalized and popularized by theoretical physicist Freeman Dyson in 1960, though it was originally put forward by a 1945 science fiction novel. Dyson assumed that the power needs of → intelligent civilizations never stops increasing. He also proposed that searching for the existence of such structures might lead to the discovery of advanced civilizations elsewhere in the Galaxy. Sometimes referred to as a → Dyson shell or → megastructure.

Freeman John Dyson (1923-). His article, entitled "Search for Artificial Stellar Sources of Infrared Radiation," appeared in the 1960 issue of Science, 131 (3414), 1667-1668; → sphere.

A → white dwarf whose spectrum shows metal lines only; no H or He.

D short for → dwarf; Z a convention; → white.

A part of the → solar corona defined by the → emission lines of hot gases. These emission lines include the so-called → forbidden lines of the strongly ionized atoms of iron, calcium, and other elements. The E corona is thinner than the → K corona and the → F corona (M.S.: SDE).

E indicating → emission; → corona.

The → Saturn's ring, with a width of 300,000 km, lying beyond the → G ring, at 180,000-480,000 km from the center of Saturn.

→ ring.

The world's largest → optical and → near infrared telescope, with a diameter of 42 m, to be built by the → European Southern Observatory (ESO). → First light is foreseen for 2018. The telescope has an innovative five-mirror design that includes advanced → adaptive optics to correct for the → atmospheric turbulence, giving exceptional → image quality. The → primary mirror will consist of almost 1000 hexagonal segments each 1.4 m across. The → secondary mirror will be 6 m in diameter. The E-ELT will collect 15 times more light than the largest optical telescopes operating today.
On 26 April 2010, the ESO Council selected Cerro Armazones as the baseline site for the E-ELT. Cerro Armazones is a mountain at an altitude of 3060 m in the central part of Chile's Atacama Desert, some 130 km south of the town of Antofagasta and about 20 km from Cerro Paranal, home of ESO → Very Large Telescope.

Short for the European Extremely Large Telescope

The time within which the amplitude of an oscillation increases or decreases by a factor e (= 2.71828...).

From e the base of the natural, or Napierian, system of logarithms; folding, from -fold suffix meaning "of so many parts," or denoting multiplication by the number indicated by the stem or word to which the suffix is attached (as in twofold; manifold), from O.E. -feald, related to Ger. -falt; Gk. altos, -plos, -plus; → time.

Zamân, → time; e, as above; tâyi noun of tâ multiplicative suffix, also "fold, plait, wrinkle; like, resembling."

1) A system for sending → messages from one individual to another via telecommunications links between → computers or → terminals using dedicated → software.
2) A message sent by email (Dictionary.com).

From electronic, → electronic, + mail, from M.E. male, from O.Fr. male "wallet, bag," of Germanic source; cf. O.H.G. malaha "wallet, bag," M.Du. male "bag;") from PIE *molko- "skin, bag."

Payel, contraction of payâm-e elelktronik "electronic message," from payâm, → message, + elektronik, → electronic; cf. Fr. mél "e-mail," from message + électronique, or courriel "e-mail," from courrier + électronique.

A → polarization component in the → cosmic microwave background radiation that depends only on → gradient, is independent of → curl and does not have → handedness. In contrast to the → B-mode, the E-mode may be due to both the → scalar perturbations and → tensor perturbations.

E, indicating electric-field like; → mode; → polarization.

The same as → elliptic aberration.

e, → elliptic; → term; → aberration.

Same as → enstatite chondrite.

→ enstatite; → type; → chondrite.

A prominent → H II region in the constellation → Serpens lying about 2 kpc away from the Sun. It measures about 30' across and surrounds the open cluster → M16 (NGC 6611), which contains at least 20 stars of spectral type B0.5 or earlier, including one 05V. At a projected distance from the cluster of about 2 pc, where the H II region has expanded into surrounding → molecular cloud, a striking → elephant trunk morphology or → pillar results. The nebula is the site of ongoing → star formation, especially in these pillar structures. The Eagle Nebula is often erroneously given the cluster's designation (M16).

Eagle, because the nebula's shape is vaguely reminiscent of an eagle in flight; from M.E. egle, from O.Fr. egle, from O.Prov. aigla, from L. → aquila "black eagle;" → nebula.

Miq, → nebula; Šâhin, → aquila.

The vertebrate organ of hearing, which is also responsible for maintaining equilibrium. It is usually composed of three parts: the outer ear, middle ear, and inner ear.

M.E. ere, O.E. eare "ear" (O.N. eyra, Dan. øre, M.Du. ore, Du. oor, O.H.G. ora, Ger. Ohr); cf. Gk. aus; L. auris; Av. usi "both ears;" Lith. ausis; O.C.S. ucho; O.Ir. au; PIE *ous-.

Guš "ear" (gušidan "to hear," niyušidan "to listen"); Mid.Pers. gôš "ear," gôšidan "to hear, listen;" O.Pers. gauša-; Av. gaoša- "ear," gaoš- "to hear;" cf. Skt. ghosa- "noise, tumult," ghus- "to sound, cry or proclaim aloud;" PIE *ghous-.

Occurring at or near the beginning of a period of time, process, or sequence of events.

M.E. erlich (adj.), erliche (adv.); O.E. ærlice, from ær "soon, ere" (from P.Gmc. *airiz, from PIE *āier- "day, morning," cf. Av. ayar- "day, day time," ayarə.drājah- "duration of one day," ayarə.bara- "day's ride," Mid/Mod.Pers. parēr "the day before yesterday," from *parā.ayer- "the day before") + -lice "-ly," adverbial suffix.

Âqâzin adj. of âqâz "beginning," from Proto-Iranian *āgaHz-, from prefix ā- + *gaHz- "to run, start," cf. Sogdian āγāz "beginning, start" (Cheung 2007).

A fairly long-lived step in the evolution of → low-mass and → intermediate-mass stars when helium burning shifts from the center to a shell around the core. At this phase the stellar luminosity is provided almost entirely by → helium shell burning. The He-shell burning generally adds mass to the growing carbon/oxygen core, resulting in → degenerate matter due to its increasing density.

→ early; → AGB; → phase.

A period in the evolution of the → solar system when the planets and satellites were in the process of formation.

→ early; → solar; → system.

A star near the beginning of the → spectral classification sequence. A star of → spectral type O, B, A, or F0 to F5. Same as → early-type star.

→ early; → spectral; → class; → star.

A qualitative term used to describe a phase in the history of the Universe, from the → Big Bang event to the apparition of the first structures (seeds of future galaxies), at a → redshift around 30.

→ early; → universe.

In the → Hubble classification, galaxies on the left part of the → Hubble sequence. Early-type galaxies tend to have redder colors, higher average surface brightnesses, and lower → neutral hydrogen content than → late-type galaxies. This terminology is based on the obsolete and erroneous idea that → elliptical and → lenticular galaxies might be evolutionary precursors to → spiral and → barred spiral galaxies.

→ early; → type; → galaxy.

Hot, luminous stars of → spectral type O, B, A, and F0 to F5. They were originally thought, wrongly, to be at an earlier stage of evolution than → late-type stars. See also → spectral classification.

→ early; → type; → star.

The third planet from the Sun. At → perihelion, it is 147,099,590 km from the Sun, and at → aphelion it is 152,096.150 km, whereas its mean distance from the Sun (→ astronomical unit) is 149,598 × 10⁶ km. Its orbital period is 365.2563 days (→ sidereal year) and its → eccentricity 0.017. Other characteristics: → axial inclination 23.44°; rotation period 23.934 h (→ sidereal day); mean density 5.52 g/cm³; mass 5.974 × 10²⁴ kg; → escape velocity 11.18 km/s; average → albedo 0.37.
The Earth's atmosphere consists of 78% nitrogen, 21% oxygen and 0.9% argon, plus carbon dioxide, hydrogen, and other gases in much smaller quantities. The atmospheric pressure at sea level is about 1,000 mbar. The surface average temperature is 15° C, but it varies, on the average, between -50° C (winter, Siberia) and up to + 40° C (summer, Sahara).
Liquid water covers 71% of the surface. Over 5,000 active volcanoes have been registered throughout man's known history. The outer layer of the planet, the → lithosphere, is covered with the → crust. In the → upper mantle and beneath the lithosphere, lies → asthenosphere. Convection in the asthenosphere has caused → plate tectonics motions and continent drifts. The densest layer of the Earth is its → core, about 3000 km to 6400 km beneath the surface, consisting primarily of iron and nickel. This core is believed to be at the origin of the magnetic field, which reaches about 3 × 10^-5 tesla near the equator. It has only one natural satellite, the Moon (M.S.: SDE).

M.E. erthe, from O.E. eorðe "ground, soil, dry land;" cf. O.N. jörð, M.Du. eerde, O.H.G. erda, Goth. airþa; from PIE base *er-.

Zamin, variant zami "earth, floor, land," Mid.Pers. zamig, Av. zam- "the earth;" cf. Skt. ksam- "the ground, earth;" Gk. khthôn, khamai "on the ground;" L. homo "earthly being" (as in homo sapiens, homicide, humble, humus, exhume), humus "the earth;" O.Russ. zemi "land, earth;" PIE root *dh(e)ghom "earth".