"of or pertaining to opposition," 1680s, from opposition + -al (1). Originally in the astronomical sense of opposition; the general sense of "having the character of hostile action" is from 1829.
type of astronomical telescope lens used for photography, 1939, named for Estonian-born German optician Bernhard Voldemar Schmidt (1879-1935), who is said to have invented it.
1610s, "action of nodding," from Latin nutationem (nominative nutatio), noun of action from past participle stem of nutare "to nod," from PIE *neu- (2) "to nod" (see numinous). Astronomical use in reference to slight periodical oscillation of the earth's axis is from 1715. Related: Nutational.
mid-15c., "90 degrees apart" (of the relative position of two heavenly bodies in astronomical measurements), from Old French quartil, from Medieval Latin quartilus "of a quartile," from Latin quartus "the fourth, fourth part" (related to quattuor "four," from PIE root *kwetwer- "four").
