Etymology
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optical (adj.)

1560s, "relating to or connected with the science of optics; pertaining to vision," from optic + -al (1). Of abstract art, from 1964. In astronomy, in reference to double stars that appear so only because they lie in the same line of sight from earth, by 1868. Optical illusion is attested by 1757. Related: Optically.

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nadir (n.)

late 14c., in astronomy, "imaginary point of the celestial sphere vertically opposite to the zenith of the sun; the inferior pole of the horizon," from Medieval Latin nadir, from Arabic nazir "opposite to," in nazir as-samt, literally "opposite direction," from nazir "opposite" + as-samt "road, path" (see zenith). Transferred sense of "lowest point" of anything is recorded by 1793.

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culminate (v.)

1640s, in astronomy, of a star or planet, "come to or be on the highest point of altitude; come to or be on the meridian," from Late Latin culminatus past participle of culminare "to top, to crown," from Latin culmen (genitive culminis) "top, peak, summit, roof, gable," also used figuratively, a contraction of columen "top, summit" (from PIE root *kel- (2) "to be prominent; hill"). Figurative sense in English of "reach the highest point" is from 1660s. Related: Culminant; culminated; culminating.

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declination (n.)

late 14c., declinacioun, in astronomy, "distance of a heavenly body from the celestial equator, measured on a great circle passing through the body and the celestial pole," from Old French declinacion (Modern French déclinaison) and directly from Latin declinationem (nominative declinatio) "a bending from (something), a bending aside; the supposed slope of the earth toward the poles; a turning away from (something), an avoiding," noun of action from past-participle stem of declinare (see decline (v.)). From c. 1400 as "a bending or sloping downward." Related: Declinational.

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binary (adj.)
"dual, twofold, double," mid-15c., from Late Latin binarius "consisting of two," from bini "twofold, two apiece, two-by-two" (used especially of matched things), from bis "double" (from PIE root *dwo- "two"). Binary code in computer terminology was in use by 1952, though the idea itself is ancient. Binary star in astronomy is from 1802.
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regress (v.)

1550s, "to return to a former state or place, go back," from Latin regressus "a return, retreat, a going back," noun use of past participle of regredi "to go back," from re- "back" (see re-) + gradi "to step, walk" (from PIE root *ghredh- "to walk, go").

In astronomy, "appear to move in a backward direction," by 1823. The psychological sense of "to return to an earlier stage of life" is attested from 1926. Related: Regressed; regressing.

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tierce (n.)
old unit of liquid measure equal to one-third of a pipe (42 gallons), 1530s, from Anglo-French ters, Old French tierce (11c.). used in the sense "one-third" in various ways, from Latin tertia, fem. of tertius "a third," from PIE *tri-tyo-, from root *trei- (see three). Also used in Middle English for "a third part" (late 15c.), "the third hour of the canonical day" (ending at 9 a.m.), late 14c., and, in astronomy and geometry, "sixtieth part of a second of an arc."
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culmination (n.)

1630s, in astronomy/astrology, "position of a heavenly body when it is on the meridian," from French culmination, noun of action from past participle stem of Late Latin culminare "to top, to crown," from Latin culmen (genitive culminis) "top, peak, summit, roof, gable," also used figuratively, contraction of columen "top, summit" (from PIE root *kel- (2) "to be prominent; hill"). Figurative sense of "highest point or summit" is from 1650s.

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trivium (n.)

by 1751, from Medieval Latin trivium (9c.) "grammar, rhetoric, and logic," the first three of the seven liberal arts, considered initiatory and foundational to the other four (arithmetic, geometry, astronomy, and music). From Latin trivium, in classical Latin "place where three roads meet; a frequented place; public street, highway," from tri- "three" (see three) + via "road" (see via). Compare trivia and also see quadrivium.

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artist (n.)

1580s, "one who cultivates one of the fine arts," from French artiste (14c.), from Italian artista, from Medieval Latin artista, from Latin ars (see art (n.)).

Originally especially of the arts presided over by the Muses (history, poetry, comedy, tragedy, music, dancing, astronomy), but also used 17c. for "one skilled in any art or craft" (including professors, surgeons, craftsmen, cooks). Since mid-18c. especially of "one who practices the arts of design or visual arts."

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