The telescope: a familiar sketch

Front matter

A FAMILIAR SKETCH

COMBINING

A SPECIAL NOTICE OP OBJECTS COMING WITHIN THE RANGE OP A

Chapter II

the Sun . . . . e 0 22

CHAPTER IIL The Earth . . . . . ' . 28

CHAPTER IY.

The Moon . . . . , * 36

CHAPTER Y.

Eclipses op the Sun and Moon , . « * 50

CHAPTER YL Meectjey and Venus . . . .59 vi

Contents.

Maes

Jupiteb

Satuen •

CHAPTER YH.

CHAPTER Till.

CHAPTER IX.

CHAPTER X.

CHAPTER XI.

Shooting- Staes and othee Luminous Meteoes

CHAPTER XII.

Fixed Staes •

CHAPTER XIII.

Clustees os1 Staes and Nebula .

Preface

Can Astronomy be presented as an entertaining study ? Has any one attempted to cull from treatises addressed to the not wholly unlearned in science, facts, and anecdotes, the "light literature " of thIS sublime study, and to tell these things in simple words ?

And to giye the interest of reality to these facts, has it been sug. gested to those who can admire and wonder at the splendour of the firmament, to try how much they can improye their view of star or planet, by examining them with the help of a small telescope, such as one may see, perchance, at every sixth window, on a fine summer's day, at a watering-place, its object-glass, capable of better things, idly directed to fishing-boat or distant steamer, or still more idly to unconscious group on the pier ?

As we believe that these attempts, namely, to relate a few of the discoveries of the learned, in words which the unlearned can understand and to tell how much may be seen of the heavenly bodies with a small telescope, have not been hitherto combined, we now venture on the task.

_ This little book does not attempt to teach Astronomy, it deals princ.pally with observation; showing how the stars appear in their season coming back year after year in their appointed time, while the stately planets move in their solemn paths, changing their places gradually among the unchanging stars, as they have done before our time, and will do when we have passed away.

Happy should we be could we impart the very great pleasure which even this humble form of Astronomy can give. The warm interest, the almost personal affection that can be felt for the well-known planet the familiar constellation, the double star that has been scanned with the little telescope is no matter of speculation with the author of this slight treatise. The delight at the first appearance in the autumn of

Preface.

glorious Orion, seen by chance at midnight, the satisfaction when Jupiter is again descried, after being some months concealed by the neighbourhood of the Sun's beams, are feelings yearly experienced by us, and little influenced by time, place, or even by circumstances. Prom foreign lands, from crowded cities, from the open windows of our quiet home, from the silent road leading from some scene of festivity, they are seen with nearly the same thoughts and feelings. They seem like friends. The distant planets are the solemn way-marks of the years that have passed since we first observed their positions ; the southern horizon hides from our view a firmament unseen by us, but nightly spread over those we know and love in distant lands. The faint comet-like spots that appear to our eyes when accustomed to the darkness, are clusters of stars, discernible even through our little telescope. But what of that wondrous belt which traverses the sky,— the Milky Way ? Our eyes and our little instrument are alike unable to decipher it ; but as we look on it we remember what has been revealed about it by a powerful telescope, namely this, " that it consists " entirely of stars scattered by millions, like glittering dust, on the black ground of the general heavens."* Stars — each, perhaps, a Sun ! Par, far away from this earth and its troubles is the mind carried by such thoughts and remembrances. And still farther may it be uplifted in this quiet hour, even to the throne of Him whom the heaven of heavens cannot contain, but who yet looks so lovingly on his creature man, from the place of his habitation.

" He healeth the broken in heart, and bindeth up their wounds. He telleth the number of the stars j he calleth them ALL by their names." — Psa. cxlvii. 3, 4.

* HerschePs ' Treatise on Astronomy,' p. 163.

THE TELESCOPE.

CHAPTER I.

THE OBSERVER'S APPARATUS j AND, WHAT TO OBSERVE.

O point out how we may see for ourselves, and to relate a little of what has been observed by others ; — these are the objects of this little book.

The latter will be attempted in succeeding chapters, and the former will form the subject of the present one.

We will suppose the reader, already interested in the appearance of the starry heavens, and acquainted, perhaps, with one or two constellations, inquiring how he may learn more, and what apparatus will be necessary for making observations.

We would answer, you should have a set of maps of the stars, an Almanack with tables of the positions of the planets, and other astronomical information, and a telescope which you can fix steadily ; we will suppose it is a good telescope, but with an object-glass only two inches in diameter,* or even less. If you are privileged

* Technically known as " two inches in aperture."

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to use a more powerful instrument at any future time, you will value it all the more from having first learned to work with a small telescope.

We have indicated the apparatus in the order which it is most desirable that the beginner should observe in using them.

First, the maps, by means of which you by degrees become acquainted with the relative position of the various stars, and in consequence able to detect the progress amongst them of one of those wandering stars, the five visible planets.

Second, the almanack, which directs the observer already instructed in the bearings of the stars, where to expect and find any given planet.

Third, the telescope, to scan the stars now familiar, and therefore additionally interesting, and to observe the planets which have been identified.

But we do not forbid the learner to reverse this order occasionally, long before the maps are mastered, and while the columns of the almanack still seem little better than a dull array of figures. He may lawfully encourage himself in his studies by looking through the telescope, pointing at random to one of the brilliant specks which he fancies may be a planet from its calm steady light. It may chance to be a discovery to him that the same telescope which enables him to read the name of a merchant brig at half a mile's distance, is also able to make the difference between a star and a planet strikingly apparent.

The planet Saturn is, while I am observing it, in a part of the heavens not far removed, in apparent

The Observer's Apparatus.

position, from the stars Castor and Pollux, or Procyon in the constellation of "the little Dog/' and to the unassisted eye is very similar to that star. But turn the telescope to each in succession; Procyon appears a brilliant diamond point, how very bright and sparkling, but how small ! Now let us see Saturn ; behold ! there is the very planet of the astronomy books, with its round disc like a tiny moon, and its broad brilliant ring. Perhaps the seldom-used night eye-piece in the telescope-case (discarded long ago, because it turned the name of the merchant brig upside down, though it did make the letters somewhat larger), may improve our view of the planet. We screw it on, removing the day eye-piece, and we can now plainly see Saturn's shadow thrown on the brilliant surface of its ring, and can faintly descry its satellite " Titan" (Plate VIII) . They look very small, it is true, but the feeling that now indeed we see an object of which hitherto we had only heard, is always vividly experienced at a first sight of Saturn. The beauty, too, of the real planet never fails to strike the beholder in a way no pictured representation can. Possibly the reader exclaims here, " I wish I had any idea where to find Saturn, or that I even knew Castor and Pollux, and the little Dog." Then study your maps, and before long no large star visible in pur latitude will be a stranger to you. We recommend maps rather than a globe for the purpose of learning the stars, for two plain practical reasons ; one is, that on the globe the stars are turned the contrary way, appearing as they would in a lookingglass, which arrangement, though necessary when the concave firmament is represented as if viewed from outside, is very confusing to a beginner. The other reason in favour of maps is that they are portable. The observer, well wrapped up, at an open window, or fairly in the open air, can so easily carry about a thin book of maps, and studying for awhile by lantern-light some one group of stars represented in it, at once turn his eyes to the stars themselves, till the same group is found and its position committed to the memory."*

A plain distinct set of maps, such as one would not mind half wearing out in the service, is much the best to learn with. The only set which the author ever used were those of Middleton's Celestial Atlas. In this work the stars visible in Great Britain are represented in five pages, engraved in the usual manner, with the lines of right ascension and declination, the equator and ecliptic, and the pictured figures of the constellations ; each page being faced by a blank map, in which the stars are vividly represented in white, on a black ground, and corresponding exactly in size and position to those on the " illustrated" page.

* A Planisphere will also be found very useful. This is an ingenious arrangement of three discs of pasteboard, by means of which all the principal stars visible in Great Britain at any given day and hour will be indicated, and the times of their rising and setting clearly pointed out.

The same information may be obtained (we need scarcely say) by a simple problem on the celestial globe; but for the mere purpose of studying the face of the heavens, the cheap and portable Planisphere is preferable. The beautiful precision and ingenious arrangements of a good celestial globe become, however, a source of great pleasure to those who have by a little persevering attention, made themselves acquainted with the actual movements of the heavens.

The Observer's Apparatus.

The advantage of this plan consists in the blank map being unencumbered with lines, figures, or names of any kind, and in its simplicity and vivid contrast of black and white bearing a resemblance to the starry firmament which it represents. The names and positions of the stars can at once be ascertained by referring to the neighbouring page.

Very lately we have met with a popular guide to the constellations, in which this plan of clear and simple maps form a prominent feature.* It is of small quarto size, and seems peculiarly well adapted for the purpose of teaching the constellations gradually, to persons hitherto acquainted with very few or with none of them ; and with a second atlas of the heavens, by the same author, t in which all the constellations are represented in four large and correct maps, would, if carefully studied on favorable evenings, from month to month, make the student thoroughly acquainted with every remarkable group, and each bright star in the glowing firmament.

We have endeavoured to attract the reader's especial attention to the circumstance that the stars visible in this latitude cannot all be seen in the course of one night ; and we now wish to state the facts of the case, and, if possible, to state them so plainly that the reader may really know how the stars appear to move.

We will suppose, reader, that with regard < to the

* 'An Easy Guide to the Constellations, with a Miniature Atlas of the Stars, and Key Maps.' By James Gall, jun.

f ' The People's Atlas of the Stars, with Key Maps ; being a companion to the Easy Guide to the Constellations/

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movements of the heavenly bodies, you know but one fact with absolute clearness and certainty, namely, that the Sun rises every day in the east, glorious and glowing from behind the horizon, and travels^ southwards in a. sloping direction till about noon, and that, as the day goes on, he evidently travels downwards, and at last sinks behind the western horizon, leaving only radiant clouds to tell of his brightness ; and that the twilight gives way to night, and again, after some hours, night to twilight, and the Sun rises again. Nay, dear reader, be not offended at this low estimate of your knowledge ; we speak only of what you know with absolute clearness and certainty, and what you have had so many more opportunities of observing than you are likely to have enjoyed with regard to the fixed stars. For how few have followed in the track of the Chaldean shepherds, they who were among the earliest to collect and hand down to succeeding ages the facts of astronomy !

Did our usual occupations, like theirs, call us to spend the whole night under the blue vault of heaven, we should soon see for ourselves, and thoroughly comprehend, that even as the Sun rises in the east, travels upwards to the south, and descends in the west, so do all the stars which we can see as we sit to watch them, facing the south, the direction where the Sun was at noon.

All the night through we should observe that there are stars rising above the horizon at our left, others drifting slowiy along opposite to us, others sinking at our right. We might also perceive that those which rise but a little way eastward of the south point which we are facing, remain but a short time in our view, never rise to any great height, and set but a little way west of the southern point of the horizon, and then remain invisible for many hours. Whereas those which rise so far to the east that we must look exactly over our left shoulder to see them emerge above the horizon, rise to a great height overhead, set far to the west, and remain so long in sight (namely, twelve hours), that the morning twilight has almost come before they have sunk at our right hand.

The stars still further removed from the south quarter of the horizon, what of them? They are still longer above the horizon, and a shorter time below than those that rise in the east. Turning our eyes completely away from the southern to the northern horizon, what do we see ? Stars which merely descend for a brief interval, and again ascend ; and above them, stars which never set at all, but slowly revolve round the almost stationary Pole Star.

But neither our present business, or we might say, the business of this little book, is with these northern stars, which indeed revolve like the others, but cannot be said to rise or set, as they are perpetually in sight on every cloudless night. We again turn our eyes to the south, and endeavour to impress on the reader that if he spent the whole of one clear night in the open air, he would see stars rising and setting, as he sees the Sun do by day. Or, without rivalling the Chaldean astronomers by actually watching all night, he may prove the same thing by observing the rising of some

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striking constellation, and tracing its progress occasionally during the night. Let him fix on one which is not too near the southern horizon, and remains a considerable time in sight, and let him view it from an east window of his house at the time of its rising, say seven o'clock in the evening, in December. He may watch it now and then till eleven o'clock, when ifc will have gone so much to his right that he will now find it easier to see it from the south side of the house.

He chances to awake at one o'clock, and now the constellation is opposite the window which looks to the south, and is higher up than the observer has previously seen it. He now closes his shutters on the calm cold stars, but, true to his undertaking, seeks his constellation again in the faint grey of the morning, shortly before seven o'clock. It is then opposite a west window, and slowly disappearing below the horizon.

Such is the progress of constellation during one night. We need hardly remind our readers that this apparent movement of the starry heavens is entirely caused by the real movement of the earth on its own axis.

We now proceed to trace the progress of a constellation during a year. Here, we have no additional movement to describe ; the stars preserve one invariable interval between the times of their rising. All the year round they come back to their old positions in twenty-three hours, fifty-six minutes, four seconds, and one-tenth of another second; in other words, the earth takes exactly that time in making one turn on its axis.

They rise at precisely the same point of the horizon

The Observer's Apparatus.

all the year round. They mount the same height in the south, and they set at the same point of the western horizon.*

Were there no brilliant SUN in our firmament to interpose its hours of daylight, and to constrain our Earth to circle round it once a year, our observations of the stars would take the following simple form.

There would be perpetual night ! and the stars alone would mark the periods of time. "We should see them rising in uninterrupted succession ; and in one cloudless interval of twenty-three hours, fifty-six minutes, four seconds, and one-tenth, the whole of the constellations would pass before our eyes, excepting those near the Southern Pole ; these, as in the existing state of things, would be perpetually invisible.

But our reader, whom we have disrespectfully supposed to be familiar with no movement of the heavenly bodies, except the rising and setting of the Sun, will naturally inquire here, " Can we not in the existing state of things see all the constellations, except those near the Southern Pole, every night ? And what has the Earth's annual movement round the Sun to say to the matter?''

Waiving the latter question for the present, we will answer the former by narrating the progress of a constellation during the several months of the year ; hoping thereby to give an idea how any persevering

* The apparent or real motions of stars, enumerated in treatises on astronomy under the names of Aberration, Precession and Nutation, Proper Motion, andx Parallax, are all so extremely slow as not sensibly to affect what is stated in the text.

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observer can see for himself that the constellations in their turns rise in the day-time, and are for some time invisible, but that they re-appear in their appointed seasons. And to one who has watched them during even a short portion of his life, they suggest the various changes of the year almost as emphatically as the opening buds, the floral splendours, the golden harvests, and the bare and leafless forests of this earth.

We have supposed an observer watching a constellation occasionally during a winter night. If he particularly noticed the minute at which one star of that constellation rose over the horizon on December 1st, he would find that this star rose near four minutes earlier on the following evening, and on December 3rd, nearly four minutes earlier still. By New Year's Day, this star, which rose at seven o'clock on December 1st, rises two hours earlier, is plainly descending to the west at one o'clock in the morning, and sets at five instead of seven.* By February 1st it rises quite in the day-time, and consequently he cannot see it till it is already high in the sky, and it sets long before the night is over. By March 1st it is rising at one in the day-time, and at one in the morning it is setting. By June 1st it is rising at seven in the morning, and is, of course, invisible all day long. At night it is below the horizon, and, therefore, invisible also. It remains visible only in. the memory of the amateur astronomer. But still observing its own invariable

* In this observation a star on the celestial equator is supposed, as it is stated, to be exactly twelve hours above the horizon. Such a star (see page 7) would rise due east of the observer.

The Observer's Apparatus.

periods, a time comes when it rises at three in the morning, namely, about the 4th of August; and should the astronomer look out for a little before the morning twilight he might see it again, soon, however, to lose it in the advancing rays of the Sun. Another month, and the star rises at one ; and thus steadily gaining its two hours a month, it at length rises at the old hour of seven in the evening, shines the whole night, and is thus again in a favorable position, for observation.

Some constellations are most conveniently placed in spring, others in autumn, others can scarcely be observed save in the short nights of summer. So whether he chooses it or not, the . observer must learn his lesson progressively. Orion, invisible during the spring and summer, and only to be seen in autumn from "the small hours of the night " till morning, glitters in the winter sky as soon as the Sun has gone far enough below the horizon. Leo brightens the southern firmament in March; and the red star of Scorpio glows in the brief interval between evening and morning in the summer months.

The changes just described in the views which we obtain of the stars are entirely caused by the Earth's annual journey round the Sun. That brilliant luminary alters his position among the stars every day by a space about equal to twice his own apparent breadth. It is in reality the Earth which moves, making the Sun appear to travel between us and those stars which lie in that part of space which is in the same plane as the Earth's " orbit/' or path.

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We cannot, it is true, see this change of position. The Sun's brightness illuminates our whole atmosphere, and conceals the stars, otherwise we should see him successfully adorning " the Earn, the Bull, the heavenly Twins/' and all the famous constellations of the Zodiac.

The stars surrounding the Sun, at least those which are most brilliant, have indeed been seen in the daytime during the brief interval of a total solar eclipse, and can at any time be detected by the accurately-adjusted telescopes, of an observatory. Our proof, however, that the Sun does thus move, or appear to move among the constellations, is, that those stars which we can see shortly after sunset, in that part of heavens opposite to the Sun, gradually diminish their distance from the region where he is placed at each successive sunset, or rather, he approaches them, till at the end of six months, they seem as if swallowed up in his beams, and are not visible at any part of the twenty-four hours. They are then behind the Sun, but time passes and they go on, and proceeding westward, have at length moved so far away, —or, as we have said, the Sun has so far moved from in front of them, or has seemed to do so in consequence of the Earth's real movement,— that they rise a little while before the Sun, and are visible again.

The maps and guides to the stars, which we have recommended, indicate the best season for observing each constellation, and commence by pointing out those northern stars which are seen all night during the whole year; proceeding next to the adjoining

The Observer's Apparatus.

constellations which can scarcely be said to set, as only a few of their stars dip for a brief period below the northern horizon.

The constellations, however, which we would especially commend to the learner's attention are those which comprise the twelve signs of the Zodiac. These signs of the Zodiac, which divide the Sun's track into twelve equal parts, do not correspond exactly with the constellations , partly owing to the unequal size of the latter and partly from another reason too complicated to be treated of in this little work. Still the Sun's path lies among these stars from west to east, and were we to mark his place in a map from day to day during a year, we should find we had traced that great circle of the heavens called " the Ecliptic/' This circle, instead of being everywhere equally distant from that star which marks the celestial pole, runs far to the south in our winter, and lies among stars which rise but a little way, comparatively, above the horizon, approaches daily northward till the middle of June, when it lies among stars which mount high in the sky, and remain, upwards of sixteen hours above the horizon. Still sweeping round the heavens, it soon begins to recede from the north pole, and travels south, till in the following winter the circle is completed.

By learning the zodiac well we shall obtain a vivid idea of the Sun's path, and rightly apprehend the reason why he appears so low in winter, so high in summer, and why we have equal day and night in the spring and autumn. Then, we shall see why the Moon, always opposite to the Sun when full, and like the Sun always travelling in the zodiac, and rising and setting along with its neighbours for the time being, is seen towering in the sky during the long winter nights, but in summer merely skirting the southern horizon.

Lastly, by knowing the zodiac, we know where to look for the five planets which are visible to the naked eye. For in that region of the heavens they pursue their course, appearing, as viewed from the Earth, like bright guests in the various constellations of the zodiac, rising and setting along with them, and appearing earlier and earlier each day, till with them they disappear behind the Sun for a while.

Here, however, our well-worn book of maps is at fault. It directs us to the steady unchanging denizens of the firmament, the fixed stars, and recognises the existence of but one wanderer, the Sun, whose place from day to day is marked on the ecliptic. The other brilliant travellers, Mercury, Venus, Mars, Jupiter, and Saturn, must be sought in the almanack every year. For instance, if the reader will possess himself of ' Dietrichsen and Hannay's Almanack/ he will find the position of any of the above planets for every fifth day during the year, clearly given in " Eight Ascension and Declination." He may find the map in which this spot of the heavens is contained, and just as we might mark the position of some remarkable spot on this earth, being given its longitude and latitude, he may neatly note the place of the planet among the stars, and forthwith prepare to search for and find it in the real heavens. The planet, thus identified, soon becomes a familiar acquaintance ; we watch it from week to week,

The Observer's Apparatus.

and in time can observe that it has its own independent movement, has changed its place in the constellation, and will at last leave it altogether. Mars, Jupiter, and Saturn are the planets most frequently in sight, while Mercury and Venus, "satellites of the Sun," as they have been termed, are seen only for a short time before the rising or after the setting of that luminary, and always in the same region of the heavens. Venus never appears further removed from the Sun than one-fourth of the celestial hemisphere ; and Mercury travels away but one-sixth, and is in fact very seldom seen, as the twilight soon conceals him from view. For a few mornings before the brighter stars have paled in the sunrise, and for a few evenings after the Sun has set, he may be seen, aptly realizing the title, " messenger of the gods," by his rapid movement. Venus is much longer in sight, occasionally remaining visible four hours after sunset, or preceding the rising of the Sun by that interval.

But Mars, Jupiter, and Saturn can be seen in quite the opposite quarter of the heavens from the Sun, and are frequently visible during the whole night. Thus we can easily trace their paths, and note them from month to month, and year to year. These planets seem to move, like the Sun, round the zodiac from west to east through the main part of their journey, yet sometimes they appear to stand still for a few days, then they actually go backward a little way, and then again they stand, then' once more move eastward. The eastward movement is real, their own steady course round the Sun, but the little backward run and the two

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