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

1) General: The quality or state of being oblique.
2) The → angle that an object's → rotational axis makes with its → orbital axis. In other words, the angle between its → equatorial plane and → orbital plane. Same as → axial tilt.

State noun of → oblique.

The angle between the Earth's → equatorial plane and the → ecliptic. Its present value is 23°26'13.5'' (or 23.43708 degrees). The effects of → precession and → nutation cause it to change between extreme values of 22.1 and 24.5 degrees over a period of approximately 41,000 years. It is currently decreasing.

→ obliquity; → ecliptic.

Elongated, usually from the square or circular form.

Late M.E. oblonge, from L. oblongus "rather long," from ob- a prefix meaning "toward, to, on, over, against" + longus, → long.

Derâzak, from derâz "long," → length + -ak suffix.

A → nitrogen (N)-rich → O-type or → B-type star.

→ O star; → B star; → nitrogen; → star.

1) Opposition to the spread of knowledge; a policy of withholding knowledge from the general public.
2) A style (as in literature or art) characterized by deliberate vagueness or abstruseness (Merriam-Webster.com).

From Fr. obscurantisme (1819), from obscurant, from obscure, from L. obscurus "dark, dusky," figuratively "unknown; unintelligible," from ob- "over" + -scurus "covered," from PIE *(s)keu- "to cover, conceal;" → -ism.

1) The act of obscuring.
2) The state of being obscured.

→ obscure; → -tion.

1a) Lacking in light or illumination; dark; dim; murky.
1b) Indistinct to the sight or any other sense.
1c) Not clear to the understanding.
2) To make dark, dim, indistinct, etc.

From O.Fr. obscur "dark, dim, not clear," from L. obscurus "covered over, dark, obscure," from ob "over" + -scurus "covered," from PIE *(s)keu- "to cover, conceal;" from which derives also the term → sky.

Tiré, from Mid.Pers. târag "dark, turbid," related to târik "dark," Mid.Pers. târig "dark," târ "darkness," Av. taθra- "darkness," taθrya- "dark," cf. Skt. támisrâ- "darkness, dark night," L. tenebrae "darkness," Hittite taš(u)uant- "blind," O.H.G. demar "twilight."
Tiré kardan compound verb with kardan "to do," → -ize.

A structure of dust and gas postulated to surround the central → black hole in an → active galactic nucleus (AGN). The presence of an obscuring torus allows the unification of the two main types of AGNs containing a → broad-line region (Type I) and a → narrow-line region (Type II), respectively. In this unified model, the two types represent the same sort of object, the appearance of which depends on the viewer's → line of sight. The best evidence for this model comes from spectropolarimetry observations of some type II AGNs in which broad → emission lines are seen in → polarized light, as would happen if the broad-line region truly were hidden, and the light were being reflected off the torus and into the viewer's line of sight.

→ obscure; → torus.

The state or quality of being obscure.

→ obscure + → -ity.

1) General: The character of something that can be observed.
2) Astro.: The possibility that an object be observable at a particular time.
3) Control theory: A measure for how well internal states of a system can be inferred by knowledge of its external outputs.

From → observable + → -ity.

1) Capable of being or liable to be observed.
2) A quantity that can be measured.
3) Quantum mechanics: A → real dynamical variable whose → eigenstates form a → complete set.

From → observe + → -able.

The extent of the Universe that we can see with the aid of the largest telescopes. Its ultimate boundary is determined by the → cosmic horizon size.

→ observable; → universe.

1) An act or instance of following a custom, rule, or law.
2) A customary practice, rite, or ceremony; a rule governing members of a religious order.
3) An act or instance of watching (Merriam-Webster.com).

→ observe; → -ance.

Nepâhdâri, on the model of negâhdâri "preservation, protection," from nepâhdâr, → observant, + -i.

1) Paying strict attention.
2) Careful in observing (Merriam-Webster.com).

→ observe + -ant, a suffix forming adjective, → -ance.

Nepâhdâr, from nepâh present stem of nepâhidan, → observe, + dâr preset stem and agent noun of dâštan, dâridan "to have, hold, maintain, possess," → protected band.

1) Act or instance of observing; → observe.
2) Careful watching of an astronomical object or event using appropriate instruments, usually for collecting data.

Verbal noun of → observe.

Pertaining to, or founded on observation, especially based on observation rather than theory.

Adj. of → observation.

That part of astrophysics that is mainly concerned with the collection of observational data, in comparison with theoretical astrophysics

→ observational; → astrophysics.

An error in observation arising from systematically favoring brighter or weaker objects or some particular object morphologies; e.g. → Malmquist bias.

→ observational; → bias.

The application of observational data to the study of the Universe as a whole.

→ observational; → cosmology.

A feature appearing in an observation, which is not intrinsic to the object observed, but is due to the inappropriate method used (e.g. limited angular resolution).

→ observational; → effect.