Richard A. Proctor

“ The examination of mere peculiarities of physical condition is, after all, but barren labour, if it lead to no discovery of physical variation. The principal charm of astronomy, as indeed of all observational science, lies in the study of change—of progress, development, and decay, and specially of systematic variations taking place in regularly-recurring cycles. And it is in this relation that the moon has been so disappointing an object of astronomical observation. ”

“ Passing over the asteroids, which are not very interesting objects to the amateur telescopist, we come to Jupiter, the giant of the solar system, surpassing our Earth more than 1400 times in volume, and overweighing all the planets taken together twice over.
Jupiter is one of the easiest of all objects of telescopic observation. No one can mistake this orb when it shines on a dark sky, and only Venus can be mistaken for it when seen as a morning or evening star. ”

“ A very moderate telescope will show her most striking features, while each increase of power is repaid by a view of new details. Yet in one sense the moon is a disappointing object even to the possessor of a first-class instrument. For the most careful and persistent scrutiny, carried on for a long series of years, too often fails to reward the observer by any new discoveries of interest. Our observer must therefore rather be prepared to enjoy the observation of recognised features than expect to add by his labours to our knowledge of the earth's nearest neighbour. ”

“ Perhaps the best method of observing Venus is to search for her when she is still high above the horizon, and when therefore the background of the sky is bright enough to take off the planet's glare. The method I have described for the observation of Mercury will prove very useful in the search for Venus when the sun is above the horizon or but just set. Of course, when an object is to be looked for high above the horizon, the two rods which support the cross-rods must not be upright, but square to the line of view to that part of the sky. ”

“ First we have the planet Mars, nearly the last in the scale of planetary magnitude, but far from being the least interesting of the planets. It is in fact quite certain that we obtain a better view of Mars than of any object in the heavens, save the Moon alone. He may present a less distinguished appearance than Jupiter or Saturn, but we see his surface on a larger scale than that of either of those giant orbs, even if we assume that we ever obtain a fair view of their real surface. ”

“ We pass to more legitimate observations, noticing in passing that Sirius is a double star, the companion being of the tenth magnitude, and distant about ten seconds from the primary. But our beginner is not likely to see the companion, which is a very difficult object, vowing to the overpowering brilliancy of the primary.
Orion affords the observer a splendid field of research. It is a constellation rich in double and multiple stars, clusters, and nebulæ. We will begin with an easy object. ”

“ Those wonderful varieties in the appearance of the solar surface which have so long perplexed astronomers, not only supply in themselves interesting subjects of observation and examination, but gain an enhanced meaning from the consideration that they speak meaningly to us of the structure of an orb which is the source of light and heat enjoyed by a series of dependent worlds whereof our earth is—in size at least—a comparatively insignificant member. ”

“ I shall merely point out that the nebula occurs in a region rich in stars, and if it is not, like the great nebula in Argo, clustered around a remarkable star, it is found associated in a manner which I cannot look upon as accidental with a set of small-magnitude stars, and notably with the trapezium which surrounds that very remarkable black gap within the nebula. The fact that the nebula shares the proper motion of the trapezium appears inexplicable if the nebula is really far out in space beyond the trapezium. ”

“ I may note here in passing that Sir John Herschel's delineation of the northern portion of the Milky Way, though a great improvement on the views given in former works, seems to require revision, and especially as respects the very remarkable patches and streaks which characterise the portion extending over Cepheus and Cygnus. It seems to me, also, that the evidence on which it has been urged that the stars composing the Milky Way are (on an average) comparable in magnitude to our own sun, or to stars of the leading magnitudes, is imperfect. ”

“ High powers in all cases increase the difficulty of observation, since they diminish the field of view and the illumination of the object, increase the motion with which (owing to the earth's motion) the image moves across the field, and magnify all defects due to instability of the stand, imperfection of the object-glass, or undulation of the atmosphere. A good object-glass of three inches aperture will in very favourable weather bear a power of about 300, when applied to the observation of close double or multiple stars, but for all other observations much lower powers should be used. ”

“ A real picture, or the image formed on the screen as in the former case, can be viewed at varying distances; but when we view the image directly, it will be found that for distinct vision the eye must be placed almost exactly at a fixed distance from the image. This peculiarity is more important than it might be thought at first sight. In fact, it is essential that the observer who would rightly apply the powers of his telescope, or fairly test its performance, should understand in what respect an image formed by an object-glass or object-mirror differs from a real object. ”

“ If the observer wait until the planet and the moon are pretty near together, he will find that it is possible to view the planet with one eye through the telescope and the moon with the unaided eye, in such a manner that the two discs may coincide, and thus their relative apparent dimensions be at once recognised. Nor should the indistinctness and incompleteness of the view be attributed to imperfection of the telescope; they are partly due to the nature of the observation and the low power employed, and partly to the inexperience of the beginner. ”

“ The quality of the stand has a very important influence on the performance of a telescope. In fact, a moderately good telescope, mounted on a steady stand, working easily and conveniently, will not only enable the observer to pass his time much more pleasantly, but will absolutely exhibit more difficult objects than a finer instrument on a rickety, ill-arranged stand. A good observing-chair is also a matter of some importance, the least constraint or awkwardness of position detracting considerably from the power of distinct vision. ”

“ One of the most interesting features of the moon, when she is observed with a good telescope, is the variety of colour presented by different parts of her surface. We see regions of the purest white—regions which one would be apt to speak of as snow-covered, if one could conceive the possibility that snow should have fallen where (now, at least) there is neither air nor water. ”

“ Those near the eastern horizon are rising, those near the western setting. Careful and continuous observation would show that the stars are all moving in the same way, precisely, as they would if they were fixed to the concave surface of a vast hollow sphere, and this sphere rotated about an axis. This axis, in our latitude, is inclined about 511⁄2° to the horizon. Of course only one end of this imaginary axis can be above our horizon. This end lies very near a star which it will be well for us to become acquainted with at the beginning of our operations. ”

“ The observer should not leave to the precious hours of the night the study of the bearing and position of the objects he proposes to examine. This should be done by day—an arrangement which has a twofold advantage,—the time available for observation is lengthened, and the eyes are spared sudden changes from darkness to light, and vice versâ. Besides, the eye is ill-fitted to examine difficult objects, after searching by candle-light amongst the minute details recorded in maps or globes. ”

“ Swayed by the attraction of this giant globe, Jupiter and Saturn, Uranus and Neptune, as well as the four minor planets, and the host of asteroids, sweep continuously in their appointed orbits, in ever new but ever safe and orderly relations amongst each other. If the sun's light and heat were lost, all life and work among the denizens of these orbs would at once cease ”

“ The star ζ, the lowest in the belt, may be tried with a 31⁄2-inch glass. It is a close double, the components being nearly equal, and about 21⁄2" apart (see Plate 3) .
For a change we will now try our telescope on a nebula, selecting the great nebula in the Sword. The place of this object is indicated in Plate 2. There can be no difficulty in finding it since it is clearly visible to the naked eye on a moonless night—the only sort of night on which an observer would care to look at nebulæ. A low power should be employed.
The nebula is shown in Plate 3 as I have seen it with a 3-inch aperture. ”

“ Let the telescope first be directed towards Vega. This orb presents a brilliant appearance in the telescope. Its colour is a bluish-white. In an ordinary telescope Vega appears as a single star, but with a large object-glass two distant small companions are seen. A nine-inch glass shows also two small companions within a few seconds of Vega. In the great Harvard refractor Vega is seen with no less than thirty-five companions. I imagine that all these stars, and others which can be seen in neighbouring fields, indicate the association of Vega with the neighbouring stream of the Milky Way. ”

“ Now, passing over the consideration that a small telescope may afford its possessor much pleasure of an intellectual and elevated character, even if he is never able by its means to effect original discoveries, two arguments may be urged in favour of independent telescopic observation. In the first place, the student who wishes to appreciate the facts and theories of astronomy should familiarize himself with the nature of that instrument to which astronomers have been most largely indebted. ”

“ If with a glass prism of a certain form we produce a spectrum of the sun, this spectrum will be thrown a certain distance away from the point on which the sun's rays would fall if not interfered with. This distance depends on the refractive power of the glass. The spectrum will have a certain length, depending on the dispersive power of the glass. Now, if we change our prism for another of exactly the same shape, but made of a different kind of glass, we shall find the spectrum thrown to a different spot. ”

“ Still, it is well for the observer who wishes systematically to survey the heavens—and who can afford the expense—to obtain a well-mounted equatorial. In this method of mounting, the main axis is directed to the pole of the heavens; the other axis, at right angles to the first, carries the telescope-tube. One of the many methods adopted for mounting equatorials is that exhibited—with the omission of some minor details—in fig. 9. a is the polar axis, b is the axis (called the declination axis) which bears the telescope. ”

“ Of course, the image becomes more sharply defined if we bring the screen nearer to the telescope, while all the details are enlarged when we move the screen away. The enlargement has no limits save those depending on the amount of light in the image. But, of course, the observer must not expect enlargement to bring with it a view of new details, after a certain magnitude of image has been attained. Still there is something instructive, I think, in occasionally getting a very magnified view of some remarkable spot. ”

“ Saturn, to be satisfactorily seen, requires a much more powerful telescope than Jupiter. A good 2-inch telescope will do much, however, in exhibiting his rings and belts. I have never seen him satisfactorily myself with such an aperture, but Mr. Grover has not only seen the above-named features, but even a penumbra to the shadow on the rings with a 2-inch telescope.
Saturn revolving round the sun in a long period—nearly thirty years—presents slowly varying changes of appearance (see Plate 7) . At one time the edge of his ring is turned nearly towards the earth ”

“ An eclipse of one satellite by the shadow of another is not a common phenomenon; in fact, I have never heard of such an eclipse being seen. That a satellite should be quite extinguished by another's shadow is a phenomenon not absolutely impossible, but which cannot happen save at long intervals.
The shadows are not black spots as is erroneously stated in nearly all popular works on astronomy. The shadow of the fourth, for instance, is nearly all penumbra, the really black part being quite minute by comparison. ”

“ The star is easily identified, since it lies to the left of Vega, forming with ζ a small equilateral triangle. A careful scrutiny suffices to indicate a peculiarity in this 49star. If our observer possesses very good eye-sight, he will distinctly recognise it as a "naked-eye double"; but more probably he will only notice that it appears lengthened in a north and south direction. [4] In the finder the star is easily divided. Applying a low power to the telescope itself, we see ε Lyræ as a wide double, the line joining the components lying nearly north and south. ”

“ As the observer's head would be placed between the object and the mirror, if the image, formed as in fig. 3, were to be microscopically examined, various devices are employed in the construction of reflecting telescopes to avoid the loss of light which would 10result—a loss which would be important even with the largest mirrors yet constructed. Thus, in Gregory's Telescope, a small mirror, having its concavity towards the great one, is placed in the axis of the tube and forms an image which is viewed through an aperture in the middle of the great mirror. ”

“ The plan of each map is such that the direction of a star or constellation, as respects the compass-points, and its elevation, also, above the horizon, at the given season, can be at once determined. Two illustrations of the use of the maps will serve to explain their nature better than any detailed description. Suppose first, that—at one of the hours named under Map I.—the observer wishes to find Castor and Pollux:—Turning to Map I. he sees that these stars lie in the lower left-hand quadrant, and very nearly towards the point marked S.E. ”

“ What causes an object to become invisible as its distance increases? Two things are necessary that an object should be visible. It must be large enough to be appreciated by the eye, and it must send light enough. Thus increase of distance may render an object invisible, either through diminution of its apparent size, or through diminution in the quantity of light it sends to the eye, or through both these causes combined. A telescope, therefore, or (as its name implies) an instrument to render 5distant objects visible, must be both a magnifying and an illuminating instrument.
Fig. ”

“ John's College, informs me that a tube of tin, covered with layers of brown paper, well pasted and thicker near the middle of the tube, forms a light and strong telescope-tube, almost wholly free from vibration.
Suffer no inexperienced person to deal with your object-glass. I knew a valuable glass ruined by the proceedings of a workman who had been told to attach three pieces of brass round the cell of the double lens. What he had done remained unknown, but ever after a wretched glare of light surrounded all objects of any brilliancy. ”