EQUATION OF TIME

equation of time, the difference between apparent time, determined by the meridian passage of the real sun, and mean time, determined by the passage of the mean sun. it goes through a double period in the course of a year. its amount varies a fraction of a minute for the same date, from year to year and from one longitude to another, on the same day. the following table shows an average value for any date and for the greenwich meridian for a number of years, from which the actual value will seldom deviate more than 20 seconds until after 1950. the + sign indicates that the real sun reaches the meridian _after_ mean noon; the - sign _before_ mean noon. _table of the equation of time._ m. s. m. s. m. s. jan. 1 +3 26 mar. 1 +12 39 may 1 -2 55 6 5 45 6 11 35 6 -3 27 11 7 51 11 10 20 11 -3 46 16 9 43 16 8 58 16 -3 51 21 11 19 21 7 30 21 -3 40 26 12 36 26 5 59 26 -3 16 feb. 1 +13 42 apr. 1 +4 9 june 1 -2 32 6 14 14 6 2 40 6 -1 44 11 14 25 11 +1 15 11 -0 48 16 14 17 16 -0 3 16 +0 14 21 13 52 21 -1 12 21 1 19 26 13 11 26 -2 10 26 2 24 july 1 +3 26 sept. 1 +0 9 nov. 1 -16 18 6 4 21 6 -1 28 6 -16 19 11 5 8 11 -3 10 11 -15 58 16 5 44 16 -4 55 16 -15 15 21 6 8 21 -6 41 21 -14 12 26 6 18 26 -8 25 26 -12 49 aug. 1 +6 10 oct. 1 -10 5 dec. 1 -11 7 6 5 47 6 -11 38 6 - 9 9 11 5 9 11 -13 2 11 - 6 57 16 4 17 16 -14 14 16 - 4 35 21 3 12 21 -15 11 21 - 2 7 26 1 55 26 -15 52 26 + 0 23 equator (late lat. _aequator_, from _aequare_, to make equal), in geography, that great circle of the earth, equidistant from the two poles, which divides the northern from the southern hemisphere and lies in a plane perpendicular to the axis of the earth; this is termed the "geographical" or "terrestrial equator." in astronomy, the "celestial equator" is the name given to the great circle in which the plane of the terrestrial equator intersects the celestial sphere; it is consequently equidistant from the celestial poles. the "magnetic equator" is an imaginary line encircling the earth, along which the vertical component of the earth's magnetic force is zero; it nearly coincides with the terrestrial equator. equerry (from the fr. _ecurie_, a stable, through its older form _escurie_, from the med. lat. _scuria_, a word of teutonic origin for a stable or shed, cf. ger. _scheuer_; the modern spelling has confused the word with the lat. _equus_, a horse), a contracted form of "gentleman of the equerry," an officer in charge of the stables of a royal household. at the british court, equerries are officers attached to the department of the master of the horse, the first of whom is called chief equerry (see household, royal).