equator
(ɪˈkweɪtə(r))
Also 7–8 æquator.
[a. late L. æquātor one who makes equal, hence in late L. (circulus) æquator diei et noctis ‘the equalizer of day and night’ (cf. equinoctial), f. æquāre to make equal, f. æquus equal.]
1. Astr. A great circle of the celestial sphere, whose plane is perpendicular to the axis of the earth. (When the sun is in the equator, day and night are equal in length: hence the name.) Commonly called the equinoctial.
| c 1391 Chaucer Astrol. i. §17 The middel cercle..is cleped also the weyere, equator of the day. 1594 J. Davis Seaman's Secr. ii. (1607) 2 When the Sunne cometh vpon the Equator, then the daies and nights are of one length through the whole worlde. 1682 Sir T. Browne Chr. Mor. 121 The time might come when capella..would have its motion in the æquator. 1726 tr. Gregory's Astron. I. ii. 295 The beginning of the Equator, from whence the Right Ascension of the Stars is reckoned, is where it intersects the Ecliptic. 1837 Whewell Hist. Induct. Sc. iii. i. §8. I. 144 The circle which divided the sphere [of the heavens] exactly midway between these poles was called the equator. |
2. Geog. A great circle of the earth, in the plane of the celestial equator, and equidistant from the two poles.
| 1612 Brerewood Lang. & Relig. xiv. 149 That the Earth on the South side of the æquator, should be of a more ponderous disposition then on the North. 1646 Sir T. Browne Pseud. Ep. II. ii. 61 The Northern pole of the Loadstone attracteth a greater weight then the Southerne on this side the Equator. 1727 Thomson Summer 647 Mountains big with mines, That on the high equator ridgy rise. 1774 Goldsm. Nat. Hist. (1776) I. 11 A polar prospect, and a landscape at the equator, are as opposite in their appearances as in their situation. 1856 Emerson Eng. Traits, Voy. Eng. Wks. (Bohn) II. 12 The sea-fire shines in her wake..Near the equator, you can read small print by it. |
| fig. a 1631 Donne Select. (1840) 105 A Christian hath no solstice..much less hath he any equator, where days and nights are equal, that is, a liberty to spend as much time ill, as well. a 1661 Fuller Worthies i. 39 It [the Reformation] is as it were the æquator, or that remarkable Line, dividing between Eminent Prelates, Learned Writers, and Benefactors to the Publick, who lived Before or After it. |
3. a. transf. A similarly situated circle on any heavenly (or, occasionally, any spherical) body.
| 1746 J. Parsons Hum. Physiognomy i. 14 Because Santorini, in his Figure of the Face, makes the Eye-lids meet upon the very Equator of the Eye-ball. 1834 Nat. Philos., Astron. iii. 83 (Usef. Knowl. Soc.) The great circle perpendicular to the axis of the moon, is called for a similar reason the equator of the moon. 1839 G. Bird Nat. Phil. 351 In a sphere of quartz..at the equator. 1868 Lockyer tr. Guillemin's Heavens (ed. 3) 37 The rapidity of this movement varies regularly with their [Sun-spots'] distance from the solar equator. |
b. magnetic equator, an irregular line, passing round the earth in the neighbourhood of the equator, on which the magnet has no dip;
= aclinic line (see
aclinic).
thermal equator, the imaginary line on the earth's surface which denotes the location of highest mean air temperature for a particular period.
| 1832 Nat. Philos., Magnetism iii. §98 (Usef. Knowl. Soc.) The magnetic equator. 1849 M. Somerville Connex. Phys. Sc. xxx. 342 A line encircling the earth, called the magnetic equator. 1930 Meteorol. Gloss. (ed. 2) 172. 1945 E. Bennett-Bremner Front-line Airline x. 65 Making due allowance for south-easterly winds to the inter-tropical front which lies on the thermal equator. |
c. equator of the magnet (see
quots.).
| 1635 N. Carpenter Geog. Del. i. iii. 60 The Magnet..is separated or diuided by a middle line or æquator. 1837 Brewster Magnet. 251 It is obvious..that the magnetic intensity increases from the equator to the poles. 1871 Tyndall Fragm. Sc. (ed. 6) I. xv. 416 Hold the needle over the equator of the magnet. 1885 S. Thompson Electr. & Magn. ii. §78 The portion of the magnet which lies between the two poles is apparently less magnetic..This region Gilbert called the equator of the magnet. |
d. Aeronautics. ‘The line along which the plane of the maximum horizontal section cuts the envelope of an aerostat’ (W. B. Faraday
Gloss. Aeronaut. Terms 1919).
| 1784 New Review July 61, 64 men who kept the machine in by ropes fixed to its equator. 1815 J. Smith Panorama Sci. & Art (1826) II. 151 From this equator proceeded ropes, by which was suspended a car in the form of a boat, a few feet below the balloon. 1838 M. Mason Aeronautica 268 An opening, however, of about four feet in length which appeared above the equator of the balloon, soon brought it down again. 1900 Westm. Gaz. 1 May 2/1 A balloon loses but little of its lifting power if a rent is made below the equator. |
e. Biol. The plane of division of a cell or nucleus lying midway between the poles and perpendicular to a line joining them.
| 1888 [see pole n.2 7]. 1896 [see equatorial a. 3]. 1908 J. A. Thomson Heredity (caption facing p. 51) The nucleus spindle has at its equator four groups of tetrads. 1913 J. W. Jenkinson Vertebr. Embryol. 95 The structure and symmetry of the egg, its axis, poles, and equator. 1961 M. J. D. White Chromosomes (ed. 5) v. 83 If there is a considerable distance between the chiasmata and the centromeres..the centromeres will be attached to the spindle about midway between the equator and the poles. |
4. attrib. and
Comb., as
equator-sun;
equatorwards adv., towards the equator.
| 1735 Thomson Liberty iv. 413 Those [paths of the sea] that, profuse Drunk by Equator-Suns, severely shine. 1875 J. Croll Climate & T. x. 187 The pressure..impels the bottom⁓water equatorwards. 1884 Daily News 2 Aug. 5/4 To continue the voyage equatorwards. |