The beauty of the heavens a pictorial display of the astronomical phenomena of the universe

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Introduction

THE want of a series of Plates for the illustration of the Science of Astronomy, of accurate, yet popular character, calculated for effective display, and still within 2 moderate compass, has led to the production of the present Work. The design comprehends 104 coloured Scenes, representing the Astronomical Phenomena of the Universe. These have been carefully executed from original drawings, paintings, and observatory studies; aided, occasionally, by appropriate pictorial embellishment, but with strict adherence to fidelity of detail.

Although these scenes may be considered as forming a tasteful Appendix to every popular treatise on Astronomy, they are accompanied by the following familiar Lecture on the Science, explanatory of the phenomena represented, so as to render recourse to other elementary works unnecessary. The design is thus made unique; and great pains have been taken to insure accuracy alike in its pictorial and scientific departments.

The Illustrations form the miniature scenery of a public exhibition, such as is occasionally witnessed in lecture-rooms; the text presenting the substance, the order, and the actual delivery of what becomes, in the present instance, a FAMILY ASTRONOMICAL LEcTURE. The prominent features of the present Work are, the novelty and simplicity of the plan, and the elegance of its execution. With its aid a family need not henceforth quit their own parlour, or drawing-room fireside, to enjoy the sublime “beauty of the heavens;” but, within their domestic circle, may, without any previous acquirements in Astronomy, become their own instructors in a knowledge of its great and leading truths and

THE

BEAUTY OF THE HEAVENS

A PICTORIAL DISPLAY

OF THE ASTRONOMICAL PHENOMENA OF

THE UNIVERSE.

EXAIBITED IN ONE HUNDRED AND FOUR SCBNES, ACCOMPANYING AND ILLUSTRATING

A Familiar Lecture on Astronomy.

FROM ORIGINAL DRAWINGS, PAINTINGS, AND OBSERVATORY STUDIES,

BY CHARLES F. BLUNT,

Lecturer on Astronomy and Natural Philosophy: Author of “The Wonders of the Telescope,” **Elementary Lecture on Astronomy,” &c., &c.

‘In the beginning God created the heaven and the earth:’’? Ganzsis i, 1.

LONDON:

MDCCCXLIX. eeee cree?

* theo

NORWICH: PRINTED BY JOSIAH FLETCHER, UPPER HAYMARKET.

INTRODUCTION.

THE want of a series of Plates for the illustration of the Science of Astronomy, of accurate, yet popular character, calculated for effective display, and still within a moderate compass, has led to the production of the present Work. The design comprehends 104 coloured Scenes, representing the Astronomical Phenomena of the Universe. These have been carefully executed from original drawings, paintings, and observatory studies; aided, occasionally, by appropriate pictorial embellishment, but with strict adherence to fidelity of detail.

Although these scenes may be considered as forming a tasteful Appendix to every popular treatise on Astronomy, they are accompanied by the following familiar Lecture on the Science, explanatory of the phenomena represented, so as to render recourse to other elementary works unnecessary. The design is thus made unique; and great pains have been taken to insure accuracy alike in its pictorial and scientific departments.

The Illustrations form the miniature scenery of a public exhibition, such as is occasionally witnessed in lecture-rooms; the text presenting the substance, the order, and the actual delivery of what becomes, in the present instance, a FamMILY ASTRONOMICAL LECTURE. The prominent features of the present Work are, the novelty and simplicity of the plan, and the elegance of its execution. With its aid a family need not henceforth quit their own parlour, or drawing-room fireside, to enjoy the sublime “beauty of the heavens;” but, within their domestic circle, may, without any previous acquirements in Astronomy, become their own instructors in a knowledge of its great and leading truths and

Oo . E iv INTRODUCTION.

phenomena. The Lecture may be read aloud by a parent, teacher, or any member of a party, the Scenes being exhibited, at the same time, in the numerical succession corresponding to their order of description. It would be impossible to devise a more rational, or, to a well-regulated mind, a more cheerful mode of passing an evening; or of inculcating the Divine lesson, of looking “through Nature up to Nature’s God.”

Each portion of the design may be said to aid the other: the scenes, by their attractive beauty, at once appeal to the eye, and can scarcely fail to impress the mind of the spectator; whilst the accompanying | details serve to reciprocate these pleasing effects, and infix them on the memory.

The Lecture is, for convenience, divided into two equal portions, so as to occupy two evenings, if desired. In its preparation, simplicity and plainness of language have been preferred to any laboured display of technical knowledge. The Author has avoided the use of such scientific terms as can be legitimately dispensed with; and has fully explained those which are requisite for perspicuity: and, extensive utility being the object in view, the omission of such matter as cannot readily be divested of difficult terms, has been preferred to the hazard of not being fully understood.

In conclusion, if the Author’s views be correct, and his mode of embodying them obtain the countenance of those whose mastery in the Science renders their approval the only true fame, his utmost hopes will be realized, and much intellectual gratification insured to the domestic circle.

LIST OF THE SCENES, AND REFERENCES TO THE DESCRIPTIONS.

SCENB. PaGs.

No. 1.—The Fixed Stars whe ne described at 3 1].—The Earth: its Form, and Position i in Space aT ae ww. 14 I1.—The Earth: its true Figure and Dimensions .. eve see 15 1V.—The Planetary System... eee aes toe ww. 19 V.—Mercury, Venus, the Earth, and Mars soe 21 VI.—The Earth, Inferior Planets, and the Asteroids, Vesta, » Jane} 21

Ceres, and Pallas sas cee ésé

VII.—The Sun's Disc cat ane iss a The Planet Mercury ioe Se ive vee VIII.—The Planet Venus ea ass ies me IX.—The Planet Mars aoe aes ose we sis The Planet Vesta se aes Ses wee és The Planet Juno ... wee sae sl ue The Planet Ceres The Planet Pallas ... a oe X.—The Planet Jupiter... a ee dae fe see XI.—The Planet Saturn te aes a ae es see XII.—The Planet Herschel, or Ureius wee = XIII.—The Moon at the Full ade ~ XIV.—The Nomenclature of the Lunar Spot

- XV.—The Moon's Phases a tes an Jos Sas ~ XVI.—The Crescent Moon.—No. 1 aa ots ~ XVII._—The Crescent Moon.—No. 2 fee ot ite ~ XVIIL—The Moon Gibbous 3 sei

~ XIX.—The Waning Moon SH ae see eis eee

X X.—The Phases of the Planet Saturn ea ate ate X XI.—The Relative Sizes of the Planets ee abs ade oc Distances of the Planets ‘es vee

The Animated Orrery _.... oe a XXII_—The Sun as seen from the different Planets eae see X XIII.—The Constellations of the Northern Hemisphere XXIV.—The Constellation Ursa Major eee ase a

acBNB. PAGE.

No. XX V.—Draco.— Ursa Minor re avo ats described at 65 Draco oes acy oe a =P ees ee we 65 XXVI.—Lynx or ie aT eee tee sas ane 65 XX VII.— Auriga ei eee wes es exe sae _ we 65 XX VIII.— Perseus Ba sos wee esi bus wee ae 66 X X1IX.— Andromeda ne as ase bos Ss eee . §66 XX X.—Cassiopeia eee sa te Des ae tas oe 66 XXXI.—Pegasus aes aia oss BRS eee see we 67 XX XIL—Cygnus—Lyra bes _ Pre es ies ao 67 XXXIII.—Cepheus_... eee aes iy bee a ive we 67 XX XIV.—Hercules ee “ee bus liso ie was oa 67 XX XV.—Bootes tie oes tes ade hue eee _ we. 67 XX XVI.— Ophiucus see die re ves ae vee or 68 XXXVIL ae maaan oes at sie . its w- 68 XX XVIII. —Aries a ais wes a3 As oe Sy 68 XX XIX.—Taurus sie se bes tee od ies sae -. 68 XL.—Gemini aes on an se ae oa sie 69 XLL—Cancer ie ae a oie its ae ois . 69 XLIL—Leo... oe ss ae ay tid es ses 69 XLIIL—Virgo ie ide gee as oe aes ww. 69 XLIV.—Libra aes its ae moa ea ae As 70 XLV.— Scorpio tne ee we ae aks oe w- 70 XLVI.— Sagittarius es aa oie see eas “se ive 70 XLVII.—Capricornus icy ae ar Te Se ase ve 70 XLVIII.— Aquarius eee sta oe see ae ves tne 70 XLIX.— Pisces 6 tee aie tee eg -. 70 L.—Monoceros and Canis "Minor reo sd Ges we ee 7 LI.—Canis Major At = ee oat uae ar we 71 LIL.—Orion Sen Te see as se “as da 71 LIII.—Cetus eee ee 3s aes _ i ww. «71 LIV.—The Sun’s Place in the Ecliptic an tee 77 LV.—The Apparent Retrograde Motion of the Planets abs we 77

LVI.—The Earth's Shadows ee eae wae a wae 7

LVII.—Eclipse of the Moon ite ee ee tis eee we 78 LVIII.— Eclipse of the Moon og See aoe ats ae 79 LIX.— Eclipse of the Sun Soe ee es oe ba5 a. 80 LX.—Eclipse of the Sun is ds Soe aS seh 80 LXI.—The Progress of an Eclipse aes ves eee avs a 80 LXIHf-—Apb Annular Eclipse of the Sun ae a0 is see 8l LXIII.—The Phenomena of the Seasons, No. I ae ce .. 8) LXIV.—The Phenomena of the Seasons. No.2... oe as 82 LXV.—The Sun at Midnight, at the North Cape sae tee oo. 83 LXVI.—The Phenomena of the Tides ies ee oie ae 83

Contents

SCENE.

No. LXVIIL—The Parallax of the Planets LXVIIL—The Transit of Venus over the Sun’s Dise LXIX.—The Eclipse of Jnpiter’s Satellites

LX X.—Comets wee ess ies LX XI.—Cometary Motion ... i se LX XII—The Laws of Planetary Motion ace a

Part I

AsTRONOMY is that science, or division of knowledge, which treats of those physical laws of existence and motion which regulate the great masses of the universe termed the heavenly bodies; which explains their mutual relations, their several actual conditions, and the "general arrangement and action resulting from their organization.

The word Astronomy, by its derivation, signifies, with AstRroLoay (with which epithet it was orginally coincident, ) the reason, interpretation, or law of the Astra, or stars. This definition of Astronomy explains to us, at once, the stupendous character of its object, with the high interest and sublimity of its inquiries and speculations. A science which presents to our consideration the greater works of creation, and engages us in the study of their direct manifestations of power, together with the unerring truth and beauty of the laws of action which govern them, will ever hold pre-eminence over other branches of human knowledge.

Of the devices proposed by active ingenuity for the popular dissemination of knowledge, oral instruction, combined with pictorial illustration, is admitted to be the most agreeable and successful, and, therefore, the most popular ; and, if the importance and dignity of the science of Astronomy be rightly considered, there will be little hesitation to conclude that ASTRONOMICAL Lectures, of a character judiciously suited to the genius and previous information of the auditory, may reasonably assume a foremost place in this mode of teaching.

Astronomy, universally acknowledged to be the most sublime and interesting of those sciences which admit of popular illustration, is doubly valuable, from its powerful influence and effects in the refinement and elevation of the human mind, and the vigour it imparts to the higher faculties.

B

Were astronomical knowledge productive of no other advantage to us, it has rendered essential service to mankind, by at once dissipating our superstitious opinions and fears. Ignorance, naturally timid, and terrified at dangers which it cannot distinctly foresee, seems ever to suspect the constancy of nature, and regards her operations with dread and apprehension; but, once clearly informed of their regularity and invariable order, it is converted into confidence, belicf, and admiration. Thus we find that the superstitions of Astrology were eradicated by the truths of Astronomy. The astrologers of old consulted the stars, under the vain pretence of searching into the designs of’ fate, and the hidden events of futurity; but the astronomer now explores the heavens, for the rational purpose of administering to the wants and necessities of mankind by useful discoveries and scientific applications of the unerring regularity of motion he finds everywhere established.

Astronomy, like every other science, was first studied, as an art subservient to the purposes of social life. The chief object of this art was to know and to mark the progress of the seasons, which depend, either immediately or remotely, on the motions and relative positions of the heavenly bodies 5° and, accordingly, some knowledge of these has, in every state of society, been a matter of the first necessity. A ready method of marking the seasons seems, in all ages, to have been the chief incitement to the study of Astronomy. It directed the labours of the field, the migration of the shepherd, and the journeys of the traveller. It was equally necessary, to regulate the appointment of public mectings, and for the record of remarkable events, The cultivation of the earth, the whole business of agriculture, depends, in fact, upon a due knowledge of the proper motions of the earth, as regards the apparent course of the sun, and the consequent changes of the scasons. In every climate there are certain intervals between the different operations of agriculture; which, once known by experience, shew the proper point of time at which those operations are respectively to be performed. But to know exactly, and even, as is often required, to know beforehand, the commencement of every season, and its stated continuance, we must be able to search the heavens for those invariable signs which are constantly connected with them, and unerringly announce their recurrence. Such signs, indicated by the position of the sun in the heavens, or by the appearance and position of particular stars—although, from the vast stuck of practical knowledge we have already obtained, they are now but little attended to—were yet, in the ancient world, when the cultivator had no other guide to direct his labours than his own simple observations, absolutely necessary for his guidance, and were a condition of his subsistence and prosperity. The presence, at certain hours, of the star Arcturus, the constellation Orion, and the Pleiades, marked out the seasons of the ancient Greeks, and the rising of the star Sirius with the sun, announced to the Egyptians the approaching inundation of the Nile, and thus prepared them for the agricultural operations which immediately followed its subsidence.

it has titious which » and armed helieh pradi- Shirs, idden r the il by ty of subas to ymevenly te of king . tlie m of y, to able ure, rth, 3 of the 10W

be OW we one ich ce cal are his

Were astronomical knowledge productive of no other advantage to us, it has rendered essential service to mankind, by at once dissipating our superstitious opinions and tears. Ignorance, naturally timid, and terrified at dangers which it cannot distinctly foresee, seems ever to suspect the constancy of nature, and regards her operations with dread and apprehension; but, once clearly informed of their regularity and invariable order, it is converted into confidence, belief, and admiration. Thus we find that the superstitions of Astrology were eradicated by the truths of Astronomy. The astrologers of old consulted the stars, under the vain pretence of scarching into the designs of fate, and the hidden events of futurity; but the astronomer now explores the heavens, for the rational purpose of administering to the wants and necessities of mankind by useful discoveries and scientific applications of the unerring regularity of motion he finds everywhere established.

Astronomy, like every other science, was first studied, as an art subservient to the purposes of social life. The chief object of this art was to know and to mark the progress of the seasons, which depend, either immediately or remotely, on the motions and relative positions of the heavenly bodies; and, accordingly, some knowledge of these has, in every state of society, been a matter of the first necessity. A ready method of marking the seasons seems, in all ages, to have been the chief incitement to the study of Astronomy. It directed the labours of the field, the migration of the shepherd, and the journeys of the traveller. It was equally necessary, to regulate the appointment of public meetings, and for the record of remarkable events, The cultivation of the earth, the whole business of agriculture, depends, in fact, upon a due knowledge of the proper motions of the earth, as regards the apparent course of the sun, and the consequent changes of the scasons. In every climate there are certain intervals between the different operations of agriculture; which, once known by experience, slew the proper point of time at which those operations are respectively to be performed. But to know exactly, and even, as is often required, to know beforehand, the commencement of every scason, and its stated continuance, we must be able to search the heavens for those invariable signs which are constantly connected with them, and unerringly announce their recurrence. Such signs, indicated by the position of the sun in the heavens, or by the appearance and position of particular stars—although, from the vast stock of practical knowledge we have already obtained, they are now but little attended to—were yet, in the ancient world, when the cultivator had no other guide to direct his labours than his own simple observations, absolutely necessary for his guidance, and were a condition of his subsistence and prosperity. The presence, at certain hours, of the star Arcturus, the constellation Orion, and the Pleiades, marked out the seasons of the ancient Greeks, and the rising of the star Sirius with the sun, announced to the Egyptians the approaching inundation of the Nile, and thus prepared them for the agricultural operations which immediately followed its subsidence.

USES OF ASTRONOMICAL KNOWLEDGE. 3

In the common affairs of life, nothing is more necessary than an exact measure of time; and, for this, it is to the heavens alone that we must look for a certain and invariable standard. From the order, and the beautiful regularity of the motions of the heavenly bodies, we obtain all our knowledge of the seasons, and the art we posscss of reckoning by certain periods of time. While the uncivilized and solitary barbarian computes his seasons by the falls of snow, or the progress of spontaneous vegetation, the astronomer refers to the heavens, and measures the regular lapse of time, and the extent of their duration, with a precision no longer to be doubted. Astronomy affords us invariable and unalterable standards by which we measure tame, extent, and motion; all great periods of time are compared with, and estimated by, the greater astronomical phenomena, as its lesser divisions are measured by the oscillations in equal times of the pendulum.

Chronology is a science so intimately and so immediately connected with astronomical observation, that, without the constant assistance and application of Astronomy, the records of history itself would possess little certainty, and the transactions of past ages would have remained to us an undigested mass of doubt. Whole nations have been swept from the earth; their arts and sciences, and even their languages, have been lost; confused and unintelligible masses of ruins alone mark the sites of the mightiest cities, and the monuments of their power and industry; and even their history survives the gencral wreck but in dark and doubtful tradition: but their astronomical observations are preserved to us; and the perfection of these, while it marks the high antiquity of the observers, fixes with accuracy the periods of their existence, and proves the state of their progress in the science.

But Astronomy affords us advantages of higher interest than even these, and of more immediate importance to the progress of civilization, and the general advancement of the world, in the assistance which it renders to the science of geography, and the art of navigation. Astronomy first demonstrated to us the true figure and circumstances of the planet we inhabit; was mainly instrumental in discovering the detail of its construction ; disclosed the nature of its true motion, and fixed its relative position in space: Astronomy it was that first inspired the adventurous mariner with confidence, and taught him to navigate the pathless ocean in perfect security !

Scene No. 1.%*—Tue Fixep Stars.

It is in the grandeur and sublimity of night, when a clear and still atmosphere affords us an undisturbed view of the starry heavens, that we gencrally receive the first practical lesson in Astronomy, and our first and most permanent impression of its beauty and its usefulness: thus we learn that, in the simplicity

* The reader is here supposed to be the lecturer, addressing his auditory.

of pastoral life, untaught shepherds were the first systematic observers of the more striking astronomical phenomena. It will be perfectly easy for a person, even wholly uninformed on the subject, to conceive that an attentive and frequent observation of this scene would enable him so far to distinguish the most remarkable stars, as to make them objects of ready reference, and even, in some degree, to classify them; forming for himself several striking groups, or configurations, and thus establishing readier and more extended means of observation.

A simple study of this nature, even if carried no further than a ready recognition of one remarkable group of stars, will afford a first and very satisfactory lesson, leading directly to the clear conviction of an important fact ; namely, that the stars are, in reality, not stationary as regards the inhabitants of the earth, but have an apparent and uniform motion from east to west, making, in strictness, one entire revolution about the earth in every twenty-four hours.

If we make our first observation in an open space looking southward, with a rough sketch, or a perfect recollection of a few such remarkable groups, from previous observation, we shall find some one of these constellations, as they may now be termed, appearing, or coming slowly into view, in the eastern quarter of the heavens; and, in a path of circular curvature, to attain, at the same slow rate of motion, its point of greatest elevation; when it arrives directly in front of us, or bearing directly south from us, to decline towards the west at the same rate, and to describe equal distances in equal times, until it finally sinks and disappears in the western quarter. We shall also observe that some groups, or single stars, seem to describe larger portions of circles than others: some will rise at the eastern point itself, and, describing a path exactly semicircular, set or disappear at the western point; others, which lie towards the south, and near to that point, will be seen to describe smaller portions, or upper segments of circles, remaining in view a much shorter time, but all of them first appearing on the eastern side of the south, and disappearing on the western side. Everything in this observation will tend to satisfy us that the stars are not stationary in the heavens, but have altogether a slow and uniform motion, in a direction from east to west.

If, on another evening, we take a station looking directly northward, and begin our observation on those groups which lie near the horizon, directly north, we shall soon discover that such groups describe complete circles in their paths; if we fix upon a group, or a remarkable star, higher above the northern horizon than the last, we shall find it will describe a smaller circle, that a group taken still higher above the horizon will describe a circle of yet smaller dimensions; and that proceeding with this examination still farther above the horizon, we arrive at a point of the heavens in which the stars appear immoveable: stars which lie very near to this point will be easily discovered, although the imaginary point itself is not actually marked by the presence of any star. One remarkable star will, however, be found very near to this point of rest, which describes so small a circle that, without very accurate

GENERAL NOTIONS OF ASTRONOMICAL PHENOMENA. 5 observation, it is difficult to determine its motion; and it is, therefore, usually considered to mark the immoveable centre of all the circular motions I have described: the point thus determined is called the Poe, and appears to the observer the only fixed spot in the visible heavens; all other parts of the expanse seem to revolve on it as their common centre: the single star here spoken of is denominated the Pote Star.

It will now be easy to imagine an immoveable right line proceeding from this star to the earth at y (Scene No. 1,) and forming what may be termed an axis to the imaginary spherical surface on which the stars seem to be placed, and on which the revolutions we have described are performed. It will be observed, that notwithstanding the perfect continuity of the apparent motion, the relative places of the stars are in no case in the smallest degree changed ; any group selected for observation may be seen as a whole in different points of its course, to become inverted to its first position, and, passing through the same degrees of obliquity in an opposite direction, to arrive at the position it occupied at the commencement of the observation, with its original appearance ; in every part of its course unerringly presenting the same part of its configurations towards the central or polar star.

If, in this stage of the inquiry, the observer can without difficulty conceive the earth he inhabits to be a vast globe floating in space, or, in more familiar language, in the air that surrounds him, we shall with facility obtain his belief that, from the other side, or what is to him the undermost side of the earth, another assemblage of stars becomes visible, similar to that he witnesses on his own. If now he be desired to repeat his early observations from his station of northern aspect, and to imagine the line he lately drew from the polar star to the earth, to be extended directly through the earth’s centre, and so forward to its surface on the southern side, he will thus obtain the place and position of a line, which, if prolonged towards the supposed stars of that quarter, will be conceived to point out a spot in the heavens in a southern direction, in which the stars have no apparent motions; and, in conformity with his observation in the northern quarter, wherein he was taught to establish a northern pole star, or central point, he will now distinctly trace the position of a similar point in the southern heavens, which he will call the southern pole; and will perceive that the entire expanse, with its assemblage of stars, above, below, and in every direction, has an apparent motion from east to west, which is performed uniformly in twenty-four hours.

The whole expanse of the heavens, with its stars, may be assimilated to an immense hollow sphere, surrounding the earth, as its centre, at an incalculable distance, having the stars posited on its inner surface, and appearing to rotate with a uniform motion, once in each day and night, on that line through the centre of the earth, as an axis, which was imagined to be drawn from the north to the south pole. Conceiving the earth to float freely, and without apparent support, as a centre, it will now appear that one-half of the expanse is visible from one side of the earth, and the other half from its opposite side. That portion in which the north pole is visible will be called the northern half, or hemisphere; the opposite portion, or that in which the south pole is visible, will be termed the southern hemisphere.

Our first scene exemplifies this lesson: here A B C D represent the earth ; 4 B C its northern hemisphere; a DC its southern hemisphere; H H the observer's horizon ; E the northern pole in the heavens; £ G the imaginary line drawn from that pole through the earth’s centre, and continued on thie other side to the southern heavens, establishing a southern pole G; the collection of stars arranged at I K L M N O represents the whole expanse of the heavens, of which 1 K L is the northern celestial hemisphere, M N 0 the southern.

Now, as to obtain a view of the south pole a, it is evidently necessary for the observer himself to travel on the earth in a southerly direction, it is evident that, as he advances in that direction, the south pole, which, at the commencement of his journey, is below the horizon, or the extent of his vision, will be gradually approaching the horizon, and that after he has travelled over a certain distance it will become visible to him ; and as the line, or axis, imagined to exist between the two poles remains fixed as to its direction, it is equally clear, that in proportion as the south pole G is thus elevated, the north pole k will be depressed. When the progress southward is thus continued until the south pole is raised from its depression below the horizon to the horizon itself, the opposite termination of the axis, or the north pole, will be depressed until it also becomes posited in the horizon, the two poles now respectively pointing out the observer’s north and south points in the horizon.

If the appearance of the heavens from this new station be now attentively observed, it will be found that the apparent motion of the stars is still performed about the same axis as before; but that the visible effect is materially different. In every entire revolution, or in the space of every twenty-four hours, the observer will now sce the whole assemblage of stars of every part of the heavens: the stars of both hemispheres will pass in succession beture him, no portion of them remaining permanently above the northern horizon, or describing entire circles as before; no portion of the southern quarter rising into view for a short period, and tlen disappearing, or any others remaining permanently below the limits of his observation ; every star, in whatever part of the heavens, becomes visible to him in its turn, and each describes in its course a semicircle of larger or smaller diameter, as it is more or less remote from the two poles, or fixed points of the axis of rotation.