Royal Astronomical Society

“ A magnificent volume on the Results of Astronomical Observations made during the years 1834–8 at the Cape of Good Hope appeared in 1847; and a catalogue of all known nebulae and clusters, amounting to 5,079, was presented to the Royal Society in 1864, while a corresponding catalogue of more than 10,000 double and multiple stars was never finished, though the materials collected for it were published posthumously in 1879. ”

“ Their Knowledge of the motion of the Heavens, for which the Arabians and the other Eastern Nations have been so deservedly famous, as their Astronomical Tables of the Longitude and Latitude of the fixed Stars, and of the appulse of the Moon to them, fully evince, is now very mean, and is chiefly studied for the use of Judiciary Astrology. The great Instrument they make use of is an Astrolabe, with which they make very imperfect Observations, having no such thing as a Quadrant or Sextant, much less a Telescope, or any mechanical Engine, to direct and assist them in their Calculation. ”

“ Of this future work, the most important, undoubtedly, is a re-survey of the temple sites, with modern instruments and methods. Next, astronomers must produce tables of the rising and setting conditions of the stars for periods far beyond those which have already been considered. The German Astronomical Society has published a table of the places of a great many stars up to 2000 B.C., but to carry on this investigation we must certainly go back to 7000 B.C., and include southern stars. ”

“ When there is a glimpse of more condensed light to be seen in the centre, it is so small that it must, be less than two-tenths of a second.
To decide whether this apparent condensed light was a real or spurious disk, I applied different limitations to the aperture of the telescope, but found that the light of the new star was too feeble to permit the use of them. From this I concluded that an increase of light might now be of great use, and viewed the asteroid with a fine 10-feet mirror of 24 inches diameter ”

“ The lineaments of the constellations remain unchanged for centuries, and, in contrast with the ceaseless movements of the planets, the stars are not inappropriately called fixed. We have, however, had more than one occasion to show throughout the course of this work that the expression "fixed star" is not an accurate one when minute quantities are held in estimation. With the exact measures of modern instruments, many of these quantities are so perceptible that they have to be always reckoned with in astronomical enquiry. ”

“ I viewed a different artificial double star with 522,7, and keeping always the same power, changed the aperture of the telescope.
With the inside rays I found them considerably unequal, and 21/2 diameters of the largest asunder. The spurious disks are perfectly well defined, round, and of a planetary aspect.
With all the mirror open, they are also round and well defined. ”

“ Scarcely in any department has there been put on record so well-directed a leap into the dark of coming discovery.
The systematic light-measurement of the stars began with the same untiring investigator. He described in 1796 the method since named that of “sequences,” and presented to the Royal Society the first of six Photometric Catalogues embracing nearly all the 2,935 stars in Flamsteed’s “British Catalogue.” They gave comparative brightnesses estimated with81 the naked eye; classification by magnitudes was put aside as vague and misleading. ”

“ If space permitted, it would be interesting to survey the progress already accomplished by modern methods of astronomical research. Hundreds of millions of stars have been photographed, and the boundaries of the stellar universe have been pushed far into space, but have not been attained. Globular star clusters, containing tens of thousands of stars, are on so great a scale (according to Shapley) that light, travelling at the rate of 186,000 miles per second, may take 500 years to cross one of them, while the most distant of these objects may be more than 200,000 light-years from the earth. ”

“ The increased light-gathering power will mean the addition of many millions of stars to those already known. Spectroscopic observations now in regular progress have carried the range of these investigations far beyond the possibilities of the 60-inch telescope. A great class of red stars, for example, almost all the members of which were inaccessible to the 60-inch, are now being made the subject of special study. And in other fields of research equal advantages have been gained. ”

“ In one group of variable stars the period of light fluctuation is directly dependent on luminosity, and knowledge of this fact enables astronomers to utilize such suns as universe lighthouses or accurate measuring points for the further exploration of distant star clusters. By this technique it is possible to measure stellar distances most precisely up to more than one million light-years. ”

“ The conclusion, then, seems to be that we are not justified in assuming that the solar system is unique simply because it differs widely from the double and multiple star systems; and that we should rather regard it as probable that the vast multitude of stars which do not appear, when viewed with the telescope, or studied by spectroscopic methods, to have any attendants comparable with themselves in magnitude, have originated in a manner resembling that of the sun's origin, and may be the centers of true planetary systems like ours. ”

“ But the number of binary stars known is not confined to those which have been discovered and measured by means of the telescope and micrometer. One of the most wonderful results of modern astronomical research has been the discovery of the fact that many stars have revolving round them invisible companions, which are either dark bodies, or else are so close to their primaries as for ever to defy the separating powers of our telescopes. The discovery of these dark, or at least invisible, companions is one of the most remarkable triumphs of the spectroscope. ”

“ If the planet be large enough the telescope will show that it possesses a disc, and has a visible and measurable circular outline. This feature a star does not exhibit. The stars are indeed so remote that no matter how large they may be intrinsically, they only exhibit radiant points of light, which the utmost powers of the telescope fail to magnify into objects with an appreciable diameter. The older and well-known planets, such as Jupiter and Mars, possess discs, which, though not visible to the unaided eye, were clearly enough discernible with the slightest telescopic power. ”

“ It fortunately happens that astrophysical research is now at the very apex of its development, founded as it is upon many centuries of astronomical investigation, rejuvenated by the introduction into the observatory of all the modern devices of the physicist, and strengthened with instruments of truly extraordinary range and power. These instruments bring within reach experiments that are in progress on some minute region of the sun's disk, or in some star too distant even to be glimpsed with ordinary telescopes. ”

“ In dealing with problems of structure and motion in the Galactic system, the 100-inch telescope offers especial advantages, because of its vast light-gathering power. Studies of radial velocities of the stars have hitherto been necessarily confined to the brighter stars, for the most part even to those visible to the naked eye. While some of these are very distant, most of the stars whose radial velocities are known belong to a very limited group, perhaps constituting a distinct cluster of which the sun is a member, but in any event of insignificant proportions when contrasted with the Galaxy. ”

“ It may be, as some astronomers hold, that most of the galactic stars are much smaller than the sun, so that their faintness is not due entirely to the effect of distance. Still, their intrinsic brilliance attests their solar character, and considering their remoteness, which has been estimated at not less than ten thousand to twenty thousand light-years (a light-year is equal to nearly six thousand thousand million miles) their actual masses cannot be extremely small. The minutest of them are entitled to be regarded as real suns, and they vary enormously in magnitude. ”

“ Our acceptance is that vast celestial vagabonds have been excluded by astronomers, primarily because their irresponsibilities are an affront to the pure and the precise, or to attempted positivism; and secondarily because they have not been seen so very often. The planets steadily reflect the light of the sun: upon this uniformity a system that we call Primary Astronomy has been built up; but now the subject-matter of Advanced Astronomy is data of celestial phenomena that are sometimes light and sometimes dark, varying like some of the satellites of Jupiter, but with a wider range. ”

“ The increasing number of those who possess astronomical telescopes, and devote more or less of their leisure in following some particular line of research, is shown by the great success in recent years of societies, such as the British Astronomical Association with its several branches, the Astronomical Society of the Pacific, and similar institutions in various parts of the world. ”

“ The two components, under the influence of powerful mutual gravitational attraction, must be revolving in a mighty orbit. Yet this vast orbit, as a whole, with the two great stars in it, must be approaching our part of the universe all the time. For the spectroscope shows the velocity of approach to increase and diminish, indeed, but it is always present. Here, then, is this great stellar system, having a four-day revolution of its own, and yet swinging rapidly through space in our direction. Nor is this all. One of the component stars must be nearly or quite dark ”

“ Up to the time of Herschel, astronomical interest centred on the solar system. Since that time it has been divided, and a great part of our attention has been given to the more distant celestial bodies. The solar system has by no means lost its interest—it has indeed gained in interest continually, as we gain in knowledge concerning it; but in order to follow the course of science it will be necessary for us to oscillate to and fro, sometimes attending to the solar system—the planets and their satellites—sometimes extending our vision to the enormously more distant stellar spaces. ”

“ As the accuracy attainable improves with experience, the proportional number of spectroscopic binaries discovered will undoubtedly be enormously increased. In fact, the star which seems not to be attended by dark companions may be the rare exception. There is the further possibility that the stars attended by massive companions, rather than by small planets, are in a decided majority; suggesting, at least, that our solar system may prove to be an extreme type of system, rather than a common or average type. ”

“ If equal portions of space really held equal numbers of stars, it is obvious that the number of stars visible in any particular direction would be strictly proportional to the range of the system in that direction, apparent accumulation being produced by real extent. The process of "gauging the heavens," accordingly, consisted in counting the stars in successive telescopic fields, and calculating thence the depths of space necessary to contain them. The result of 3,400 such operations was the plan of the Galaxy familiar to every reader of an astronomical text-book. ”

“ It is clear that if the telescope moves while the stars are tracing out their little trails on the plate, the circularity of the curves will be disturbed. Now, ordinary astronomical telescopes are always mounted upon very stable foundations, well adapted to making the telescope stand still; but the polar telescope which we wish to use in a research fundamental to the entire science of astronomy ought to possess immobility and stability of an order higher than that required for ordinary astronomical purposes. ”

“ If the stars were at rest, or if a sufficient number of stars were taken to eliminate the consequences of their individual motions, then the spectroscopic search for the movements of the solar system becomes very simple. It is only necessary to measure the rate at which the solar system alters its distance from the various points around. That point on the celestial sphere where the star shows the velocity of approach to be greatest, can only be the point towards which the solar system is directing its motion. ”

“ We have no reason to believe that telescopes will ever be constructed so powerful as to magnify a stellar image into an actual disk. With our present knowledge we therefore may not expect that the great flames and other evidences of eruptive phenomena, which we believe from inference to be as characteristic of the stars as of the sun, will ever become visible. We must therefore depend for a knowledge of such phenomena upon the one star whose surface can be studied in detail. Armed with this knowledge, we may trace out with the spectroscope successive. ”

“ There is no reason to think that “temporary” or new stars ever appear a second time.
Admiral Smyth has well said, “It checks one’s pride to recollect that if our sun with the whole system of planets, asteroids, and moons, and comets were to be removed from the spectator [Pg 146] to the distance of the nearest fixed star, not one of them would be visible, except the sun, which would then appear but as a star of perhaps the 2nd magnitude. ”

“ It is many years, however, since any book has dealt with the telescope itself, apart from the often repeated accounts of the marvels it discloses. The present volume contains neither pictures of nebulæ nor speculations as to the habitibility of the planets; it merely attempts to bring the facts regarding the astronomer’s chief instrument of research somewhere within grasp and up to the present time.
The author cordially acknowledges his obligations to the important astronomical journals, particularly the Astro-physical Journal, and Popular Astronomy in this country ”