An Etymological Dictionary of Astronomy and Astrophysics

1a) An opinion that one reaches or to which one commits oneself on the basis of probability alone or in the absence of any evidence whatever.

1b) The act of forming such an opinion.

2a) To arrive at or commit oneself to an opinion about (something) without having sufficient evidence to support the opinion fully.

2b) To estimate or conjecture about correctly (Dictionary.com).

Etymology (EN): M.E. gessen, perhaps from Scandinavian; cf. Sw., Dan., Norw. gissa, M.L.G. gissen, M.Du. gessen, related to verb get.

Etymology (PE): Hads, from Ar. Hads “intuition, conjecture, surmise.”

1. To → control or direct the → motion or course of.
   

2. Something that directs the motion or points the way. → autoguider, → guide star, → guider, → lightguide, → waveguide.

Etymology (EN): M.E. giden (v.), from O.Fr. guider “to guide, lead,” from Frankish *witan “show the way” (cf. Ger. weisen “to show, point out,” wissen “to know;” O.E. witan “to see”). Cognate with Pers. bin- “to see” (present stem of didan “to see”); Mid.Pers. wyn-;
O.Pers. vain- “to see;” Av. vaēn- “to see;”
Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see.”

Etymology (PE): Râh bordan “to guide, conduct,” from râh “path, → way,” + bordan “to carry, lead,” → vector.

A relatively bright star conveniently located in the → field of view used for → guiding.

See also: → guide; → star.

Same as → guiding telescope.

A → technique used in astronomical → observations to keep the → telescope→ tracking in pace with the → rotational motion of the → Earth. Guiding consists of maintaining the → image of a star motionless during the observation. See also → guiding accuracy, → guiding telescope, → offset guiding, → autoguiding.

See also: Verbal noun of → guide.

The accuracy (expressed in arcseconds) with which a → telescope follows the → rotational motion of the → Earth.

See also: → guiding; → accuracy.

In the → epicyclic theory of → galactic rotation, the center of the → epicycle.

See also: → guide; → center.

A telescope which is attached to a second telescope being used for photographic purposes. The guiding telescope, mounted parallel to the optical axis of the main telescope, is used by the observer to keep the image of a celestial body motionless on a photographic plate.

See also: → guiding; → telescope.

A nebula resembling a guitar produced by a → neutron star, which is travelling at a speed of 1600 km per sec! The neutron star leaves behind a “wake” in the → interstellar medium, which just happens to look like a guitar (only at this time, and from our point of view in space). The Guitar Nebula is about 6.5 light years away, in the constellation → Cepheus, and occupies about an arc-minute in the sky, corresponding to about 300 years of travel for the neutron star.

See also: Guitar, ultimately from Gk. kithara “cithara,” a stringed musical instrument related to the lyre, perhaps from Pers. sehtar “three-stringed,” from sé “three” + târ, → string. → nebula.

A deep → inlet of the sea almost surrounded by land, with a narrow mouth; a large deep → bay (OxfordDictionaries.com).

Etymology (EN): M.E. go(u)lf, from O.Fr. golfe, from It. golfo, from Gk. Gk. kolpos “bay, gulf of the sea,” originally “bosom.”

Etymology (PE): Xalij, ultimately from Proto-Ir. *garika-, from *gar- “to soak, moisten” (+ relation suffix -ika-, → -ics; notably the variant Tabari -ij, as in Yušij); cf. Gilaki *xal-, xâlə “stream, brook” (as in the stream names Cam.xâlə, Zât.xâlə, Hašu.xâlə, etc.), Tabari câl in Câlus (name of a river in Mâzandarân); Laki cal.ow “marsh;” Tabari kela, kila “stream;” Baluci kor “river;” Iranian rivers Kor (in the Fârs Province), Kârun and Karxé (both in Xuzestân); in classical Pers. literature kul, kul.âb “pond, reservoir,” (prefixed far-) far.qar “a minor stream derived from a more considerable one; the bed of a river when almost dry, the small quantity of water remaining in such a river” (Steingass); âqâridan, âqeštan, farqâridan “to moisten, wet, macerate;” Dari Yazd qeriz “saliva;” Râvar, Bardsir, Kerman geriz “saliva;” Laki xur “swamp;” Tâti xer “cloud;” Bandare Jâski gerâh “moisture;” Ossetic I. qaryn/qard “to permeate, seep through (of liquid);” Shughni (prefixed) ažär- “to soak, wet;” Roshani (prefixed) nižêr-/nižêrd “to soak, wet;” Skt. gal- “to drip;” O.H.G. quellan “to well, to gush;” Ger. Quell, Quelle “source.” Note that, according to the classical Pers. dictionary Borhân-e Qâte’ compiled in India (17th century), xalij is a Pers. word and not Arabic. Similarly, M.A. Emâm-Shushtari, in his “Dictionary of Persian Words in Arabic,” remarks that the Arabic root XLJ is irrelevant to the “gulf” sense.

A trench or ravine worn away by running water in the earth.

Etymology (EN): Gully, a variant of M.E. golet “water channel,” from O.Fr. goulet, dim. of goule “throat, neck,” from L. gula; cf. Mod.Pers. galu “throat,” geri, geribân “collar,” gerivé “low hill,” gardan “neck;” Mid.Pers. galôg, griv “throat,” gartan “neck,” Av. grīvā- “neck;” Skt. gala- “throat, neck,” Gk. bora “food;” L. vorare “to devour;” PIE base *g^wer- “to swallow, devour.”

Etymology (PE): Âbkand, literally “dug by water,” from âb “water” (Mid.Pers. âb “water;” O. Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
Hitt. happa- “water;” PIE āp-, ab- “water, river;”
cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis); O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook”)

• kand, contraction of kandé, p.p. of kandan “to dig” (Mid.Pers. kandan “to dig;” O.Pers. kan- “to dig,” akaniya- “it was dug;” Av. kan- “to dig,” uskən- “to dig out” (→ ex- for prefix us-); cf. Skt. khan- “to dig,” khanati “he digs”).

An immense emission nebula about 40° across lying toward the southern constellations → Vela and → Puppis. It contains the → Vela pulsar and the → Vela supernova remnant, and seems to be created by an outburst of ionizing radiation that accompanied a → supernova explosion.

See also: Named after its discoverer, the Australian astronomer Colin Stanley Gum (1924-1960); → nebula.

The continuum trough observed in the spectra of high redshift quasars (z> 6) at the blue wing of their Lyman-alpha emission line (1216 Å). It is explained by the
scattering of the radiation of the quasar by intergalactic neutral hydrogen on the line of sight. Because of the cosmological expansion, the quasar line is redshifted
with respect to the continuum trough. The Gunn-Peterson opacity increases rapidly with redshift. It is interpreted as a strong evidence for the reionization of the Universe around z = 6.

See also: After James E. Gunn and Bruce A. Peterson who predicted the effect in 1965; → effect.