YEAR. 



The folar year is either agronomical ox civil. 



Year, Solar AJlronomical, is that determined precifely by 

 the obfervations of aftronomy ; and is of two kinds, tropical 

 2nd JiJcreal or ajtral. 



Year, Tropical or Natural, is the time which the fun 

 employs in paffing through the zodiac, or from one equinox, 

 or one tropic, to the fame again ; which, as before ob- 

 ferved, is 365 days, 5 hours, 49 minutes ; or, more accu- 

 rately, 365 d. 5 h. 48' 48". This is the only proper or 

 natural year, becaufe it always keeps the fame feafons to 

 the fame months. 



In order to find the tropical year, obferve the meridian 

 altitude, a, of the fun on the day neareft to the equinox ; 

 then the next year take its meridian altitude on two follow- 

 ing days, one when its altitude, m, is lefs than a, and the 

 next when its altitude, n, is greater than a, then « — m is the 

 increafe of the fun's declination in 24 hours ; alfo, when the 

 declination has increafed by the quantity a ■— m from the 

 time when the meridian altitude, m, was obferved, the de- 

 clination will then become a ; and as we may confider the 

 increafe of declination to be uniform for a day, we have 

 n — m : a — m :: 24 hours, the interval from the time 

 when the fun was on the meridian on the firft of the two 

 days, till the fun has the fame declination a, as at the ob- 

 fervation the year before ; and this time, added to the time 

 when the fun's altitude m was obferved, gives the time 

 when the fun's place in the ecliptic had the fame fituation 

 in refpeft to the equinoftial points, which it had at the 

 time of the obfervation the preceding year ; and the in- 

 terval of thefe times is the length of a tropical year. 



If, inftead of repeating the fecond obfervation the next 

 year, there be an interval of feveral years, and you divide 

 the interval between the times when the declination was 

 found to be the fame, by the number of years, you will get 

 the tropical year more exadlly. 



Year, Sidereal or AJlral, is the fpace of time in which 

 the fun, going from any fixed ftar, returns to the fame. 

 This confifts of 365 days, 6 hours, 6 minutes, 11,5 fe- 

 conds. 



To find the length of a fidereal year. On any day when 

 the fun is at Z on the meridian [Plate 'X.X.l.Jig. 12.), take 

 the difference, Z m, between the fun's right afcenfion when 

 it paffes the meridian, and that of a fixed ftar, S ; and when 

 the fun returns to the fame part of the heavens the next 

 year, compare its right afcenfion with that of the fame ftar 

 for two days, one when their difference, b m, of right afcen- 

 fions is lefs, and the other when the difference, fm, is greater 

 than the difference, Z m, before obferved ; then bf is the 

 increafe of the fun's right afcenfion in the time, / ; and as 

 the increafe of right afcenfion may be confidered as uniform 

 for a fmall time, we have i/ : A Z :: / : the time, T, in 

 which the right afcenfion is increafed from 3 to Z ; this 

 time, T, therefore, added to the time of the obferved right 

 afcenfion at b, gives the time when the fun is at the fame 

 diftance, Z m, in right afcenfion from the ftar, which it was 

 when obferved at Z the year before ; the interval of thefe 

 limes is therefore the length of the fidereal year. The beft 

 time for thefe obfervations is about March 25, June 20, 

 September 17, December 20, the fun's motion in right 

 afcenfion being then uniform. Inftead of obferving the 

 diflerence of the right afcenfions, you may obferve that of 

 their longitudes. 



If, inflead of repeating the fecond obfervations the year 

 after, there be an interval of feveral years, and you divide 

 the obferved intervsl of time when the difference of their 

 right afcenfions was found to be equal, by the number of 



years, you will have the length of a fidereal year more 

 exaftly. 



The preceflion being given ( fee Precessio.v ) , and alfo the 

 length of a tropical year, the length of a fidereal year may 

 be found by this proportion; 360° — 5o",25 : 360= •■ 

 365 d. jh. 48' 48" : 365 d. 6h. 9' III" the length of 

 the fidereal year. 



Year, /Inomaliflical, is the time that elapfes from the 

 fun's leaving its apogee till it returns to it : and as the pro- 

 greffive motion of the apogee in a year is 1 1",75, the anoma- 

 liftical year muft be longer than the fidereal year, by the 

 time which the fun takes in moving over 1 1",75 of longi- 

 tude at its apogee ; but when the fun is in its apogcf , 

 its motion in longitude is 58' 13" in 24 hours: hence 

 58' 13" : ii",75 :: 24 hours : 4' ^of", which added to 

 365 d. 6h. 9' iii", gives 365 d. 6h. 14' 2^", the length 

 of the anomahftical year. M. de la Lande determined this 

 motion of the apogee from the obfervations of M. de la 

 Hire, and thofe of Dr. Maflcelyne. Caffini made it the fame. 

 This year is fometimes ufed by aftronomers. See Asoma- 

 LISTICAL Tear. 



Year, Civil, is that form of year which each nation has 

 contrived for the computation of time : or the civil is the 

 tropical year, confidered as only confifting of a certain 

 number of whole days ; the odd hours and minutes being 

 fet afide, to render the computation of time in the common 

 occafions of life more eafy. 



Hence, as the tropical year i» 365 days, 5 hours, 48 

 minutes, 48 feconds, the civil year is 365 days. And 

 hence, alfo, as it is neceffary to keep pace with the heavens, 

 it is required that every fourth year (hould confift of 366 

 days. 



Hence, laftly, the civil year is either common or bijfex- 

 tile. 



Year, the Common Civil, is that confifting of 365 days. 

 This, therefore, has feven months of 3 i days each, four of 

 30 days, and one of 28 days ; according to the well-known 

 canon : 



Thirty days hath September, 

 April, June, and November. 

 February twenty -eight tilone. 

 And all the reft have thirty-one. 

 Year, Bijextile, or Leap, is that confifting of 366 days ; 

 or it has one day extraordinary ; which day is called the 

 intercalary, or bijfextile day. 



This intercalary, or additional day to every fourth year, 

 was firft appointed by Juhus Caefar ; who, to make the 

 civil year keep pace with the tropical ones, contrived that 

 the fix hours which the former wanted of being equal to the 

 latter, fhould, in four years, make a whole day, and be added 

 before the twenty-fourth, or to the twenty-third of Fe- 

 bruary, which was their fixth of the calends of M?.rch. 

 Hence, as in that year, they reckon this day twice over, or 

 add bis fexto cakndas, the year itfelf came to be called lis 

 fextus, and Bijextile ; which fee. 



The intercalary day, however, among us, is not intro- 

 duced by telhng the twenty-third of February twice over, 

 but by adding a day after the twenty-eighth of February ; 

 which month, in that year, contains twenty-nine days. See 

 'L^E.^v■Tear. 



A farther reformation in this year was made by pope 

 Gregory. See Gregorian Year, and Calendar- 



Year, Lunar, is a fyftem of twelve lunar months. See 

 Lunar. 



Hence, from the two kinds of fynodical lunar months 

 tlicrc arife two kinds of lunar years ; the one aflrcnomical, 



the other cii»l. 



H 2 ^ k-'.h. 



