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So is the tangent of the sun's ASTRODICTICUM, an astronodeclination

mical instrument invented by Mr. To the sine of the ascensional Weighel, by means of which seve. difference.

ral persons may view the same When the latitude and declina star at the same time. tion have the same name, the ASTROGNOSIA, signifies a difference between the right as knowledge of the fixed stars, their cension, and the ascensional differ-names, ranks, situations, &c. ence, is the oblique ascension; ASTROLABE, the Dance of an and their sum is the oblique de-ancient astronomical instrument, scension; but when they are of very much resembling our armila contrary names, the sun is the lary sphere. oblique ascension, and the differ. It is likewise the name of an inence is the oblique descension. strument formerly much used at

ASCII, are those inhabitants of sea for ascertaining the allitude of the globe, who, at certain times of the sun, stars, &c. which consisted the year, have no shadow ; such of a brass ring about titleen inches are all those who inhabit the lor. in diameter, gradualed into derid zone.

grees and minutes, and fitted with ASPECT, in Astronomy, is the an index moveable about its censituation of the stars and planets tre, and carrying two sights; the with regard to each other. There whole being attached to a small are tive principal aspects; which, brass ring for suspending the inwith their respective characters, strument at the time of observation. are as follows: viz.

Modern astronomers use the term Ó, Conjunction, when the

Astrolabe, to denote a stereogra. angle contained between

phic projection of the sphere, 0

either upon the plane of the equaany two planels is .

tor, the eye being supposed to be *, Sextile, when the angle? in the pole of the world; or upon

60° is •••••

the plane of the meridian, when

the eye is supposed in the point of 0, Quartile, when the an

90° the intersection of the equinoctial gle is

and horizon. A, Trine, when the angle is 120°

ASTRONOMICAL, any thing re

lating to astronomy. 8, Opposition, when the

180°

ASTRONOMY, a mixed matheangle becomes

matical science, which treats of When the planets have exactly the heavenly bodies, their mo. the distances described above, tions, periods, eclipses, magni. they are called partile aspects ; studes, &c. and of the causes on and when the distances have not which they depend. That part of precisely these measures, they are the science which relates to the called platic aspects.

motions, magnitudes, and periods ASPERITY, the roughness or of revolution, is called Pure or inequality in the surface of bodies. Plain Astronomy: and that which

ASSURANCE on Lives. See investigates the causes and law's LIVES.

by which these motions are reguASTEROIDS, in Astronomy, a lated, is called Physical Astronomy. name given by Dr. Herschel to the History of Astronomy.- The early four new planets discovered by history of this science, like that of the foreign astronomers Piazzi, all others of ancient date, is too Olbers, and Harding.

much disfigured by fabulous and ASTERISM, in Astronomy, an an- allegorical representations, lo adcient term, siguifying the same as mit of any regular or satisfactory CONSTELLATION.

elucidation. It is probable, how. ASTRÆA, in Astronomy, a name ever, that some knowledge of this given by some authors to the sign kind must have been nearly coVirgo.

eval with the formation of society. ASTRAL, depending or belonging Many traces of it have been to the stars ; as ASTRAL year, &c. I found amongst various nations,

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æra.

which show that several of the employ the time the sun moves 1°
most remarkable celestial pheno- in the ecliplic. Their sidereat
mena must have been observed, year consists of 365d, br, 12m, 308 3
and a knowledge of thein dissemi- and the tropical, of 3650, 51, 50m,
nated, at a very reniote period. 3.58. They assign inequalities to
But in what age or country the the motions of the planets, answer.
science first originated, or by ing very well to the annual paral.
whom it was gradually methodised lax, and the equation of the cen-
and improved, is extremely un- tre.
certain.

Most authors, however, fix the M. Bailly, in his elaborate his origin of astronomy and astrology tory of ancient and modern astro. either in Chaldea, or in Egypt; nomy, endeavours to trace the ori. and, accordingly, among the an. gin of this science among the Chalo cients, we find the word Chaldean deans, Egyptians, Persians, Indi. often used for astronomer, or asans, and Chinese, to a very early trologer. Both of these nations period. And thence, he maintains, pretended to a very high antiquity, that it was cultivated in Egypt and and claimed the honour of produChaldea 2800 years before Christ; cing the first cultivators of this in Persia, 3209 ; in India, 3101 ; and science. The Chaldeans boasted in China, 2952 years before that of their temple, or Tower of Belus,

He also apprehends, that and of Zoroaster, whom they placed astronomy had been studied even 5000 years before the desli uction long before this distant period, of Troy: while the Egyptians spoke and that we are only to date its with equal pride of their colleges revival from this time.

of priests, where astronomy was In investigating the antiquity laughit; and of the monunieni of and progress of astronomy among Osymandyas, in which, it is said, the Indians, M. Bailly examines there was a golden circle of 365 and compares four different sets of cubits in circumference, and one astronomical tables of the Indian cubit thick, divided into 365 equal philosophers; namely, that of the parts, answering to the days of the Siamese, explained by M. Cassini year, &c. in 1689; that brought from India From Chaldea and Egypt, the by M. le Genuil, of the Academy science of astronomy passed into of Sciences; and two other manu- Phenicia, and was by that people script tables, found aniong the applied to the purposes of navigapapers of the late M. de Lisle; all tion, whence they became masters of which he found to accord toge- of the sea, and of almost all the ther, and all referring to the meri-commerce in the world. The dian of Benares. It appears that Greeks, it is probable, derived the fundamental epoch of the In- their astronomical knowledge chief. dian astronomy, is a remarkable ly from the Egyptians and Phenici. conjuncticn of the sun and moon, ans, by means of several of their which took place at the distance country men who visited those naof 3102 years before Christ: and tions for the purpose of learning M. Bailly informis us, that by our the different sciences. most accurate astronomical tables, Several of the constellations are such a conjunolion did really hap- mentioned by Hesiod and Homer, pen at that time. He farther on. who lived 870 years before Christ. serves, that at present the Indians The knowledge of the Greeks in calculate eclipses by the mean mo- this science, was greatly iniproved tious of the sun and moon com- by Thales the Milesian, and others, mencing at a period 5000 years dis who travelled into Egypt. Thales tant.

was born about 640 years before The solar year of the Brahmins Christ; and was the first among of Tervalore is divided into twelve the Greeks who observed stars, the anequal months, each being equal solstices, the eclipses of the sun to the time the sun occupies in and moon, and predicted an eclipse moving through a sign; and in of the sun. The science was far. their calculations for a day, they/ther cultivated and extended by

56

13

reans.

his successors, Anaximander, Anax-, and motions of the heavenly bo
imenes, and Anaxagoras; but most dies.
especially by Pythagoras, who Hipparchus, who flourished
having resided a long time in about 140 years before Christ, was
Egypt, &c. brought thence the the first who applied himself to
learning of the Egyptians, taught the study of every part of this sci-
the same in Greece and Italy, and ence; and, as we are infornied by
founded the sect of the Pythago- Ptolemy, made great improve-

He taught that the sun was ments in it; he discovered that the in the centre of the universe; that orbits of the planets are eccentric, the earth was round, and people that the moon inoved slower in the had antipodes; that the moon re. apogee than in her perigee, and flected the rays of the sur, and that there was a motion of antici. was inhabited like the earth; that pation of the moon's nodes; he comets were a kind of wandering constructed tables of the motions stars, disappearing in the farther of the sun and moon, collected parts of their orbits; that the white accouuts of such eclipses, &c. as colour of the milky way was owing had been made by the Egyptians to the united brightness of a great and Chaldeans, and calculated all multitude of small stars; and he that were to happen for 600 years supposed that the distances of the to come: he discovered that the moon and planets from the earth, fixed stars changed their places, were in certain harmonic propor. having a slow motion of their own tions to one another.

from west to east; he corrected Philolaus, a Pythagorean, who the Calippic period, and pointed flourished about 450 years before out some errors in the method of Christ, asserted the annual motion Erastosthenes for measuring the of the earth about the sun; and not circumference of the earth; he long after, the diurnal motion of computed the san's distance more the earth, on its own axis, was accurately than any of his prede. taught by Hicetus a Syracusian. cessors: but his chief work is a About the same time, Neton and catalogue which he made of the Euclemon flourished at Athens, fixed stars, to the pumber of 1022, where they observed the summer with their longitudes and latitudes, solstice 432 years before Christ; and apparent magnitudes; which, and observed the risings and set with niost of his other observatings of the stars, and to what sea- tions, are preserved by Ptolemy in sons they answered, Meton also in- his Almagest. vented the cycle of nineteen years, But little progress was made in which still bears his name.

astronomy from the time of HipEratosthenes, who was born at parchus in that of Ptolemy, who Cyrene in the year 271 before was born at Pelusium in Egypt, in Christ, measured the circumfer. the first century of the Christian ence of the earth; and being in- era, and who made the greatest vited from Athens to Alexandria, part of his observations at the ce. by Ptolemy Euergetes, and made lebrated school of Alexandria in keeper of the royal library there, that country. Profiting by the obhe set up for that prince those ar- servations of Hipparchus, and other millary spheres, which Hipparchus ancient astronomers, he formed a and Pioleny afterwards employed system of his own, whiclı, though so successfully in observing the erroneous, was followed for many heavens. He also determined the ages by all nations: he compiled distance between the tropics to be the Almagest, which contained the

of the whole meridian circle, observations and collections of which makes the obliquity of the Hipparchus, and others of his pre. ecliptic, in his time, to be 23° 51}. decessors in astronomy; a perThe celebrated Archimedes also formance which will ever be valu. cultivated astronomy, as well as able to the professors of that scigeometry and mechanics; and con- ence. This work was preserved structed a kind of planetarium, or from the conflagration of the Alex orrery, to represent the pheuomenalandrian Library, and translated

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grave of Hesse-Cassel, made a great discovered, by trials, that the cubes number of observations, published of the distances of the planets from by Snelius in 1618, and preferred the sun were in the same propor. y Hevelius to inose of Tychotion as the squares of their perioBrahe. From these observations dical times of revolution. By obhe formed a catalogue of 400 stars, servations also on comets, he conwith their latitudes and longitudes, cluded that they are freely carried and adapted them to the beginning about among the orbits of the of the year 1593.

planets, in paths that are nearly Tycho Brahe, a Dane, began his rectilinear; but which he could observations about the same time not then determine. See Dr. Small with the Landgrave of Hesse, and on the discoveries of Kepler. observed the great conjunction of About this time much was done Jupiter and Saturn; but finding by Wright, Napier, Bayer, Mercathe usual instrumenis very inaccu-tor, Maurolycus, Magnius, Homerate, he constructed many others, lius, Schulter, Steven, Galileo, much larger and more exact. In Thomas and Leonard Digges, John 1571, he discovered a new star in Dee, Robert Hood, Harriot, &c. the chair of Cassiopeia ; which in The beginning of the seventeenth daced him, Jike Hipparchus on a century was particularly distinsimilar occasion, to make a new guished by the invention of telescatalogue of the stars; which he copes, and the application of them composed to the nuinber of 777, to the purposes of astronomy. and adapted their places to the Hevelius, from his own curious year 1600. Tycho invented a sys- observations, furnished a catalogue iem to account for the planetary of fixed stars, much more complete motions; but he is more to be noted than Tycho's. Huygens and Cas. on account of his accurate obser: sini discovered the satellites of vations, which lended much to the Saturn and his ring. And Gassen. discovery of the real nature of the dus, Horrox, Bullialdus, Ward, planetary orbits.

Ricciolus, Gascoign, &c. each conWhile Tycho resided at Prague, tributed very considerably to the with the emperor, he prevailed on improvement of astronomy. Kepler to leave the University of Newtou demonstrated, from phyGlatz and to come to him; and sical consideration, the great law Tycho dying in 1601, Kepler en that regulates all the heavenly mo. joyed the title of mathematician to tions, sels bounds to the planetary the emperor ; who ordered him to orbs, determined their greatest ex. finish the tables of Tycho Bralie, cursions from the sun, and their which he published in 1627, under nearest approaches to him. It was the title of Rodolphine. He died he who first discovered whence about the year 1630, at Ratisbon, arose that constant and regular where he was soliciting the arrears proportion, observed by both pri. of his pension. From his own ob- mary and secondary planets, in servations, and those of Tycho, their circulation round their cenKepler discovered several of the iral bodies; and their distances true laws of nature, by which the compared with their periods. He motions of the celestial bodies are also gave a new theory of the regulated. He discovered that all moon, which accounts for all her' the planets revolve about the sun, inequalities from the laws of gra. not in circular but in elliptical vity and mechanics. orbits, having the sun in one of the Mr. Flamstead was appointed foci of the ellipse; that their mo the first astronomer royal at Green. tions are not equable, but. varying wich in 1675. He observed, for quicker or slower, as they are near forty-four years, all the celestial to the sun, or farther from him ; phenomena, the sun, moon, planets, that the areas described by the and fixed stars; of all which he variable line drawn from the planet gave an improved theory and to the sun are equal in equal times, tables. Cassini also, the first and always proportional to the French astronomer royal, very times of describing them. He also much distinguished himself, mak

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