zir- (#), ir-
A prefix occurring originally in loanwords from L. but freely attached to elements of any origin and used with the meaning "under, below, beneath."
From L. preposition sub "under" (also "next to, up to, toward"), from PIE base *upo- "from below," hence "turning upward, upward, up, over, beyond;" cf. O.Pers. upā (prep.) "under, with;" Av. upā, upa (prep.; prevb) "toward, with, on, in" (upā.gam- "to arrive at," upāpa- "living in the water," upa.naxturušu "bordering on the night"); Mod.Pers. bâ "with," from abâ; Skt. úpa (adv., prevb., prep.) "toward, with, under, on;" Gk. hypo "under;" Goth. iup, O.N., O.E. upp "up, upward."
Zir- "below, down;" Mid.Pers. azêr "below, under," êr "below, down; low, under," adar "low;" Av. aδara- (adj.), aδairi- (prep.) "below;" cf. Skt. ádhara- "lower;" L. infra (adv., prep.) "below, underneath, beneath," inferus "lower;" O.E. under "under, among"); PIE base *ndher.
A measure of angle smaller than 1 arcsecond, usually until 0.1 arcsecond.
Imaging in excellent seeing conditions using an adequate detector to obtain stellar images whose profile lies in the sub-arcsecond range.
A part of a larger image.