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

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.

To watch carefully or note for a scientific or special purpose, e.g. to observe a star (astronomy), to observe the behavior of a patient (medicine, psychology), an animal (ethology, zoology), social groups (sociology), etc.

From O.Fr. observer, from L. observare "watch over, look to, attend to, guard," from ob "over" + servare "to watch, keep safe," from PIE base *ser- "to protect;" cf. Av. har- "to guard, observe, pay attention to," haraiti "guards, keeps," harətar- "protector, watcher," harəθra- "guarding, protection," hāra- "watched, guarded," Mod.Pers. zinhâr "beware!, mind!," Gk. heros "protector, hero."

Note 1: Observation is the most important basis of empirical sciences. All theories rely on observation, and must finally be supported by observational evidence. Persian, in contrast to European languages, lacks a distinct term that recognizes observation as a conceptual premise of sciences. In astronomy the Ar. rasad (رصد) is currently used, while in classical astronomical texts the Pers. pâyidan (پاییدن) is used mainly by prominent figures like Biruni and Tusi. However, the term rasad is never used for cases outside astronomy. The situation for other sciences is not clear. Often one resorts to the Ar. loanword mošâhedé "to look at each other," which lacks ability to form derivatives. Therefore, here we suggest a term that can be used in all fields of knowledge.

Nepâhian, from ne- + pâhidan. The prefix ne- "down; into" (as in negâh "look, glance," negaristan "to view, look at," nešastan "to sit down," nemudan "to display") from O.Pers./Av. ni- "down, into;" cf. Skt. ni "down," nitaram "downward," Gk. neiothen "from below," cf. E. nether, O.E. niþera, neoþera "down, downward, below, beneath," from P.Gmc. *nitheraz, Du. neder, Ger. nieder; PIE *ni- "down, below."
The second component pâhidan, variants pâyidan, pâsidan "to watch, observe, look steadily;" Mid.Pers. pây- "to protect, guard;" Sogdian p'y "to observe, protect, watch over;" O.Pers. pā- "to protect," pāta- "protected;" Av. pā- "to protect," pāti "guards," nipā(y)- (with ni-) "to watch, observe, guard," nipātar- "protector, watcher," nipāθri- "protectress;" cf. Skt. pā- "to protect, keep," tanû.pā- "protecting the body," paś.pā- "shepherd;" Gk. poma "lid, cover," poimen "shepherd;" L. pascere "to put out to graze," pastor "shepherd;" Lith. piemuo "shepherd;" PIE base *pā- "to protect, feed."

Note 2: Since pây-, pâyidan is used for → conserve, we adopt the variant pâh-, pâhidan, which is extant in Lâri and Gerâši dialects; cf. Gilaki pâstan, pâssan "to guard, pay attention." In fact the interchange of phonemes h, i and s is not rare in Indo-European languages.

Note 3: Examples of pâyidan "to observe" in astronomy, from Biruni's al-Tafhim (written c. 1029 A.D.)
p. 313: و بپای ارتفاع آ فتاب را.
p. 64: و بپای تا بدایره اندر آید.

Note 4: As indicated above, nepâh- exists in Av. as nipāy- "to watch, protect."