The Astronomy of Milton's 'Paradise Lost' by Thomas Nathaniel Orchard (easy books to read in english TXT) 📕

books on astronomy. In 1773 he borrowed a small telescope, which he used for observational purposes, and was so captivated with the appearances presented by the celestial bodies, that he resolved to dedicate his life to acquiring ‘a knowledge of the construction of the heavens.’ This resolution he nobly adhered to, and became one of the most distinguished of astronomers. Like many other astronomers, Herschel possessed the requisite skill which enabled him to construct his own telescopes. Being desirous of possessing a more powerful instrument, and not having the means to purchase one, he commenced the manufacture of specula, the grinding and polishing of which had to be done by hand, entailing the necessity of tedious labour and the exercise of much patience. After repeated failures he at length completed a 5½-foot Gregorian reflector, and with this instrument made his first survey of the heavens. Having perceived the desirability of possessing a more powerful telescope, he equipped himself with a reflector of twenty feet focal length, and it was with this instrument that he made those wonderful discoveries which established his reputation as a great astronomer.

On March 31, 1781, when examining the stars in the constellation Gemini, Herschel observed a star which presented an appearance slightly different to that of the other stars by which it was surrounded; it looked larger, had a perceptible disc, and its light became fainter when viewed with a higher magnifying power. After having carefully examined this object, Herschel arrived at the conclusion that he had discovered a comet. He communicated intelligence of his discovery to the Royal Society, and, a notification of it having been sent to the Continental observatories, this celestial visitor was subjected to a close scrutiny; its progressive motion among the stars was carefully observed, and an orbit was assigned to it. After it had been under observation for some time, doubts were expressed as to its being a comet, these were increased on further examination, and eventually it was discovered that this interesting object was a new planet. This important discovery at once raised Herschel to a position of eminence and distinction, and from a star-gazing musician he became a famous astronomer. A new planet named Uranus was added to our system, which completes a revolution round the Sun in a little over eighty-four years, and at a distance of near 1,000 millions of miles beyond the orbit of Saturn. Herschel’s name became a household word. George III. invited him to Court in order that he might obtain from his own lips an account of his discovery of the new planet; and so favourable was the impression made by Herschel upon the King, that he proposed to create him Royal Astronomer at Windsor, and bestow upon him a salary of 200l. a year. Herschel decided to accept the proffered appointment, and, with his sister Caroline, removed from Bath to Datchet, near Windsor, in 1782, and from there to Slough in 1786. In 1788 he married the wealthy widow of a London merchant, by whom he had one son, who worthily sustained his father’s high reputation as an astronomer. Herschel was created a Knight in 1816, and in 1821 was elected first President of the Royal Astronomical Society. He died at Slough on August 25, 1822, when in the eighty-fourth year of his age, and was buried in Upton Churchyard.

It is inscribed on his tomb, that ‘he burst the barriers of heaven;’ the lofty praise conveyed by this expression is not greater than what Herschel merited when we consider with what unwearied assiduity and patience he laboured to accomplish the results described in the words which have been quoted. By a method called ‘star-gauging’ he accomplished an entire survey of the heavens and examined minutely all the stars in their groups and aggregations as they passed before his eye in the field of the telescope. He sounded the depths of the Milky Way, and explored the wondrous regions of that shining zone, peopled with myriads of suns so closely aggregated in some of its tracts as to suggest the appearance of a mosaic of stars. He resolved numerous nebulæ into clusters of stars, and penetrated with his great telescope depth after depth of space crowded with ‘island universes of stars,’ beyond which he was able to discern luminous haze and filmy streaks of light, the evidence of the existence of other universes plunged in depths still more profound, where space verges on infinity. In his exploration of the starry heavens Herschel’s labours were truly amazing. On four different occasions he completed a survey of the firmament, and counted the stars in several thousand gauge-fields; he discovered 2,400 nebulæ, 800 double stars, and attempted to ascertain the approximate distances of the stars by a comparison of their relative brightness.

It had long been surmised, though no actual proof was forthcoming, that the law of gravitation by which the order and stability of our system are maintained exercises its potent influence over other material bodies existing in space, and that other systems, though differing in many respects from that of ours, and presenting a more complex arrangement in their structure, perform their motions subject to the guidance of this universal law. The uncertainty with regard to the controlling influence of gravity was removed by Herschel when he made his important discovery of binary star systems. The components of a binary star are usually in such close proximity that, to the naked eye, they appear as one star, and sometimes, even with telescopic aid, it is impossible to distinguish them individually; but when observed with sufficient magnifying power they can be easily perceived as two lucid points. Double stars were for a long time believed to be a purely optical phenomenon—an effect created by two stars projected on the sphere so as to appear nearly in the same line of vision, and, although apparently almost in contact, situated at great distances apart. At one time Herschel entertained a similar opinion with regard to those stars. In 1779 he undertook an extensive exploration of the heavens with the object of discovering double stars. As a result of his labours he presented to the Royal Society in 1782 a list of 269 newly discovered double stars, and in three years after he supplemented this list with another which contained 434 more new stars. He carefully measured the distances by which the component stars were separated, and determined their position angles, in order that he might be able to detect the existence of any sensible parallax. On repeating his observations twenty years after, he discovered that the relative positions of many of the stars had changed, and in 1802 he made the important announcement of his discovery that the components of many double stars form independent systems, held together in a mutual bond of union and revolving round one common centre of gravity.

The importance of this discovery, which we owe to Herschel’s sagacity and accuracy of observation, cannot be over-estimated; what was previously conjecture and surmise, now became precise knowledge established upon a sure and accurate basis. It was ascertained that the law of gravity exerts its power in regulating and controlling the motions of all celestial bodies within the range of telescopic vision, and that the order and harmony which pervade our system are equally present among other systems of suns and worlds distributed throughout the regions of space. The spectacle of two or more suns revolving round each other, forming systems of greater magnitude and importance than that of ours, conveyed to the minds of astronomers a knowledge of the mechanism of the heavens which had hitherto been unknown to them.

During the many years which Herschel devoted to the exploration of the starry heavens, and when engaged night after night in examining and enumerating the various groups and clusters of stars which passed before his eye in the field of his powerful telescope, he did not fail to remember the sublime object of his life, and to which he made all his other investigations subordinate, viz., the delineation of the structural configuration of the heavens, and the inclusion of all aggregations, groups, clusters, and galaxies of stars which are apparently scattered promiscuously throughout the regions of space into one grand harmonious design of celestial architecture.

Having this object in view, he explored the wondrous zone of the Milky Way, gauged its depths, measured its dimensions, and, in attempting to unravel the intricacies of its structure, penetrated its recesses far beyond the limit attained by any other observer. Acting on the assumption that the stars are uniformly distributed throughout space, Herschel, by his method of star-gauging, concluded that the sidereal system consists of an irregular stratum of evenly distributed suns, resembling in form a cloven flat disc, and that the apparent richness of some regions as compared with that of others could be accounted for by the position from which it was viewed by an observer. The stars would appear least numerous where the visual line was shortest, and, as it became lengthened, they would increase in number until, by crowding behind each other as a greater depth of stratum was penetrated, they would, when very remote, present the appearance of a luminous cloud or zone of light. After further observation Herschel was compelled to relinquish his theory of equal star distribution, and found, as he approached the Galaxy, that the stars became much more numerous, and that in the Milky Way itself there was evidence of the gravitation of stars towards certain regions forming aggregations and clusters which would ultimately lead to its breaking up into numerous separate sidereal systems. As he extended his survey of the heavens and examined with greater minuteness the stellar regions in the Galactic tract, he discovered that by his method of star-gauging he was unable to define the complexity of structure and variety of arrangement which came under his observation; he also perceived that the star-depths are unfathomable, and discerned that beyond the reach of his telescope there existed systems and galaxies of stars situated at an appalling distance in the abysmal depths of space. Though the magnitude of that portion of the sidereal heavens which came under his observation was inconceivable as regards its dimensions, Herschel was able to perceive that it formed but a part—and most probably a small part—of the stellar universe, and that without a more extended knowledge of this universe, which at present is unattainable, it would be impossible to determine its structural configuration or discover the relationships that exist among the sidereal systems and Galactic concourses of stars distributed throughout space. Herschel ultimately abandoned his star-gauging method of observation and confined his attention to exploring the star depths and investigating the laws and theories associated with the bodies occupying those distant regions.

Since all the planets if viewed from the Sun would be seen to move harmoniously and in regular order round that body, so there may be somewhere in the universe a central point, or, as some persons imagine, a great central sun, round which all the systems of stars perform their majestic revolutions with the same beautiful regularity; having their motions controlled by the same law of gravitation, and possessing the same dynamical stability which characterises the mechanism of the solar system.

The extent of the distance which intervenes between our system and the fixed stars constituted a problem which exercised the minds of astronomers from an early period until the middle of the present century.

Tycho Brahé, who repudiated the Copernican theory, asserted as one of his reasons against it that the distances by which the heavenly bodies are separated from each other were greater than even the upholders of this theory believed them to be. Although the distance of the Sun from the Earth was unknown, Tycho was aware that the diameter