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OBSERVATORY

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Originally appearing in Volume V19, Page 955 of the 1911 Encyclopedia Britannica.
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OBSERVATORY . Up to a comparatively See also:

recent date an " observatory " was a See also:place exclusively devoted to the taking of astronomical observations, although frequently a rough See also:account of the See also:weather was kept. When the progress of terrestrial See also:magnetism and See also:meteorology began to make See also:regular observations necessary, the See also:duty of taking these was often thrown on astronomical observatories, although in some cases See also:separate institutions were created for the purpose. In this See also:article the astronomical observatories will be chiefly considered. Up to about 300 B.C. it can scarcely be said that an observatory existed anywhere, as the crude observations of the heavens then taken were only made by individuals and at intervals, employing the simplest possible apparatus. Thus, according to See also:Strabo. See also:Eudoxus had an observatory at See also:Cnidus. But, when See also:philo-. ophical See also:speculation had exhausted its resources, and an See also:accumulation of facts was found to be necessary before the knowledge of the construction of the universe could advance farther, the first observatory was founded at See also:Alexandria, and continued in activity for about four See also:hundred years, or until the See also:middle or end of the and See also:century of the See also:Christian era. See also:Hipparchus of See also:Rhodes, the founder of See also:modern See also:astronomy, by repeating observations made at Alexandria, discovered the precession of the equinoxes, and investigated with considerable success the motions of the See also:sun, See also:moon and See also:planets. His See also:work was continued by more or less distinguished astronomers, until See also:Ptolemy (in the and century A.D.) gave the astronomy of Alexandria its final development. When See also:science again began to be cultivated after the dark ages which followed, we find several observatories founded by Arabian princes; first one at See also:Damascus, next one at See also:Bagdad built by the See also:caliph Al-See also:Mamun See also:early in the 9th century, then one on the Mokattam near See also:Cairo, built for See also:Ibn Yunis by the caliph Iiakim (about See also:I000 A.D.), where the IJakimite tables of the sun, moon and planets were constructed. The Mongol khans followed the example; thus arose the splendid observatory at See also:Maragha in the See also:north-See also:west of See also:Persia, founded about A.D.

1260 by Hulagu See also:

Khan, where Nasir Uddin constructed the Ilohkhanic tables; and in the 15th century the observatory at See also:Samarkand was founded by Ulugh Beg, and served not only in the construction of new planetary tables but also in the formation of a new See also:catalogue of stars. With the commencement of scientific studies in See also:Europe in the 15th century the See also:necessity of astronomical observations became at once See also:felt, as they afforded the only See also:hope of improving the theory of the motions of the See also:celestial bodies. Although astronomy was taught in all See also:universities, the taking of observations was for two hundred years See also:left to private individuals. The first observatory in Europe was erected at See also:Nuremberg in 1472 by a wealthy See also:citizen, Bernhard See also:Walther, who for some years enjoyed the co-operation of the celebrated astronomer See also:Regiomontanus. At this observatory, where the work was continued till the founder's See also:death in 1504, many new methods of observing were invented, so that the revival of See also:practical astronomy may be dated from its See also:foundation. The two celebrated observatories of the 16th century, Tycho See also:Brahe's on the Danish See also:island of Hven (in activity from 1576 to 1597) and that of See also:Landgrave See also:William IV. at See also:Cassel (1561-1597), made a See also:complete revolution in the See also:art of observing. Tycho Brahe may claim the See also:honour of having been the first to see the necessity of carrying on for a number of years an extensive and carefully-planned See also:series of observations with various See also:instruments, worked by himself and a See also:staff of assistants. In this respect his observatory (Uraniburgum) resembles our modern larger institutions See also:mare closely than do many observatories of much more recent date. The mighty impulse which Tycho Brahe gave to practical astronomy at last installed this science at the universities, among which those of See also:Leiden and See also:Copenhagen were the first to found observatories. We still find a large private observatory in the middle of the 17th century, that of Johannes Hevehus at See also:Danzig, but the foundation of the royal observatories at See also:Paris and See also:Greenwich and of numerous university observatories shows how rapidly the importance of observations had become recognized by governments and public bodies, and it is not until within the last hundred and See also:thirty years that the development of various new branches of astronomy has enabled private observers to compete with public institutions. The instruments employed in observatories have of course changed considerably during the last two hundred years. When the first royal observatories were founded, the See also:principal instruments were the mural quadrant for measuring See also:meridian See also:zenith distances of stars, and the See also:sextant for measuring distances of stars inter se, with a view of determining their difference of right See also:ascension by a See also:simple calculation.

These instruments were introduced by Tycho Brahe, but were subsequently much improved by the addition of telescopes and micrometers. When the See also:

law of See also:gravitation was discovered it became necessary totest the correctness of the theoretical conclusions See also:drawn from it as to the motions within the See also:solar See also:system, and this necessarily added to the importance of observations. By degrees, as theory progressed, it made greater demands for the accuracy of observations, and accordingly the instruments had to be improved. The transit See also:instrument superseded the sextant and offered the See also:advantage of furnishing the difference of right ascension directly; the clocks and chronometers were greatly improved; and lastly astronomers began early in the loth century to treat their instruments, not as faultless apparatuses but as imperfect ones, whose errors of construction had to be detected, studied and taken into account before the results of observations could be used to test the theory. That century also witnessed the See also:combination of the transit instrument and the mural quadrant or circle in one instrument—the transit or meridian circle. While the necessity of following the sun, moon and planets as regularly as possible increased the daily work of observatories, other branches of astronomy were opened and demanded other observations. Hitherto observations of the " fixed stars " had been supposed to be of little importance beyond fixing points of comparison for observations of the movable bodies. But when many of the fixed stars were found to be endowed with " proper See also:motion," it became necessary to include them among the See also:objects of See also:constant See also:attention, and in their turn the hitherto totally neglected telescopic stars had to be observed with precision, when they were required as comparison stars for comets or See also:minor planets. Thus the See also:field of work for meridian instruments became very considerably enlarged. In addition to this, the increase of See also:optical See also:power of telescopes revealed hitherto unknown objects—See also:double stars and nebulae—and brought the study of the See also:physical constitution of the heavenly bodies within the range of observatory work. Researches connected with these matters were, however, for a number of years chiefly left to See also:amateur observers, and it is only since about 183o that many public observatories have taken up this See also:kind of work. The application of spectrum See also:analysis, See also:photometry, &c., in astronomy has still more increased the number and variety of observations to be made, while the use of See also:photography in work of precision has completely revolutionized many branches of practical astronomy.

It has now become necessary for most observatories to devote themselves to one or two See also:

special See also:fields of work. It would be difficult to arrange the existing observatories into classes either according to the work pursued in them or their organization, as the work in many cases at different times has been directed to different objects, while the organization depends mostly on See also:national and See also:local circumstances. As already alluded to above, one of the principal characteristics of the larger observatories of the See also:present See also:day is the See also:distribution of the work among a number of assistants under the See also:general superintendence of a director. This applies principally to the See also:great observatories, where the sun, moon, planets and a limited number of fixed stars are without interruption being observed, but even among these institutions hardly two are conducted on the same principles. Thus in Greenwich the instruments and observations are all treated according to strict rules laid down by the astronomer-royal, while in See also:Washington or Pulkowa each astronomer has to a certain extent his choice as to the treatment of the instrument and arrangement of the observations. The same is the See also:case with the smaller institutions, in most of which these arrangements vary very much with See also:change of personnel. The way in which the results of observations are published depends principally on the See also:size of the institutions. The larger observatories issue their " See also:annals " or " observations " as separate periodically-published volumes, while the smaller ones chiefly depend on scientific See also:journals to See also:lay their results before the public, naturally less fully as to details. Subjoined is a catalogue of public and private observatories still in activity in 1910 or in existence within the past hundred years. (4f°= 1° of See also:long.) (Abbreviations: ap., See also:aperture; equat., See also:equatorial; obs., observatory or observations; o.g., See also:object-See also:glass; phot., photographic; refl., reflector; refr., refractor; s.g., silvered glass; vis., visual; univ., university.

End of Article: OBSERVATORY

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