Fig. 2. CONSTELLATIONS OF THE GREATER AND LESSER BEAR, AND THE POLE STAR.
HOW TO OBSERVE THE HEAVENS.
Dr. Dionysius Lardner
[Extracted from Museum of Science and Art,
vol. 7, (1854), p. 145-68.]
1. Spectacle presented by the firmament. 2. Useful observations
can be made without astronomical instruments. 3. Apparent motion of the
firmament. 4. The meridian. 5. View of the circumpolar region. 6. Permanency of
the form of the stellar groups. 7. The celestial sphere. 8. The celestial poles.
9. Orders of magnitude of the stars. 10. Number of stars of each order. 11.
Constellations. 12. Ursa major. 13. Antiquity of the name. 14. Sometimes called
Waggon, Wain, or Chariot. 15. Number of stars in it. 16. Proper names of
[p.146] stars. 17. Use of the imaginary figure to express the position of the stars. 18.
Ursa minor: the pole star. 19. How it makes a nocturnal clock. 20. Arctic
circle: origin of the name. 21. Cassiopeia's chair. 22. Pegasus and Andromeda.
23. Perseus. 24. Auriga. 25. General view of the region of these constellations:
Capella, Vega, Adrided, and Altair. 26. Orion.
1. To all persons in whose minds a taste for the study of nature has been awakened, there is no spectacle which excites an interest so intense as that which is offered by the firmament on a clear night; and to such there is no occupation more pleasing than from season to season to observe on clear nights the changes which take place in that glorious scene. But to render such contemplation still more agreeable, and to enable the intelligent spectator to turn his observations to profitable account, it is necessary that he should render himself familiar with the objects which are there presented in such countless numbers and endless variety.
2. It is a great error to suppose that all useful astronomical observations must necessarily be confined to observatories, and that no one can taste the pleasures offered by practical astronomy who is not supplied with telescopes and other optical and astronomical apparatus. Our Maker has given us, in the eye, an instrument of exquisite structure, and has supplied us with an understanding, by which that organ may be directed to the most sublime speculations. But even when it is useful that the natural limits of our organs of vision may be extended, and their aim directed with greater precision by artificial and scientific aid, much may be accomplished by the most simple and economical means. A common opera-glass will often give us a distinct view of numerous objects which would otherwise escape the naked eye. The most ordinary telescope will be still more useful. And those who occupy themselves habitually with the celestial scenery, so as to be familiarised with its general features, character, and apparent motions, will not be slow to contrive various simple expedients by which the relative position of objects can be ascertained and measured and the succession of their appearances and disappearances anticipated.
We shall therefore, on the present occasion, endeavour to give such plain and simple rules as may enable every one, by the mere use of his eyes, and still more by the occasional use of such optical aids as are almost universally accessible, to occupy himself advantageously with the contemplation of the heavens.
3. Let us then suppose a person totally ignorant of astronomy to stand with his face directed to the south, and to view the heavens on a clear starlight night. No long time will elapse before he will be rendered conscious that the splendid panorama [p.147] presented to him is not stationary. In the course of an hour, he will observe that various objects which were visible above the horizon on his right have disappeared; and that, on the contrary, a corresponding number of objects, which were not visible above the horizon on his left, have come into view. By further attention he will perceive that the objects which were at the mid-heavens, in the direction due south, are now no longer so, but have descended towards the right, that is, towards the west, while objects which were to the left of the mid-heavens will have risen to that region.
4. To assist our explanation, let us imagine the entire firmament divided by a line or great circle, rising from the point of the horizon towards which the observer is supposed to look, and being carried vertically upwards to pass over his head, and to descend behind him to the northern point of the horizon. This great line of division, which is called the celestial meridian, divides the whole visible firmament into two equal parts; one lying to the west, or to the right, and the other to the east, or to the left, of the observer.
By continuing his attentive observation of what goes on before him, he will soon perceive that all the objects visible upon the firmament are in motion. That they rise on the east side; that they ascend to the meridian; and then, descending to the west, pass below the horizon and disappear.
5. Let us now suppose our observer to face round and direct his view to the north. A different spectacle will be presented to him. Supposing him to be placed in these climates, he will soon ascertain that the chief part of the objects which are visible in the firmament do not appear and disappear; that is, they do not rise and set. If, for example, any such object be observed upon the celestial meridian over his head so soon after sunset as the stars become visible, he will observe it from hour to hour to descend on his left, that is, towards the west, and to depart more and more from the meridian. So far, however, this is what equally took place when he looked to the south, and had the west upon his right. But after the lapse of a certain time he will find different appearances to be manifested. At the end of about three hours from the time the object referred to began to depart from the meridian, it will be found to have attained a certain limit of distance from the meridian, which will not be exceeded. After this it will begin, on the contrary, again to approach the meridian; but, in doing so, will also approach the horizon, as though it were ultimately destined to set. Such, however, will not be the case; for, at the end of twelve hours, if the return of daylight be sufficiently retarded to enable our observer still to see [p.148] the object, it will have returned to the meridian, without having gone below the horizon or disappeared.
In thus passing from an elevated point of the meridian to another point much lower, the object in question will appear to move over a semicircle of the heavens, of which the part of the meridian between the point from which it departed and the point at which it arrives is the diameter.
If the same object could be seen during the succeeding twelve hours, it would be observed to move over the corresponding semicircle to the east of the meridian, that is, to the right of the observer; and, at the end of this second interval of twelve hours, the object would return to that more elevated point of the meridian from which it started.
Such an object, therefore, never rises or sets; and if the presence of the sun did not render it invisible during the day, it might be seen to revolve continually in a circle of the heavens divided into two equal semicircles, east and west, by the meridian, completing its revolution in such circle, and therefore returning to the same point of the meridian, after an interval of about twenty-four hours.
What has been here stated respecting a single object, is true, with certain qualifications, of an immense number of objects visible to an observer looking to the north, as here supposed. All such objects like that described appear to revolve in circles, but not all in the same circle. Some will be found to revolve in greater, and some in lesser, circles; but all such circles are characterised by two most remarkable circumstances, the first of which is, that they all have the same centre, which is a certain point on the celestial meridian; and the second is, that all the objects which move in them, complete their revolution in precisely the same time.
Such being then the general character of the changes which the scene presented by the heavens to the observer undergoes, let us consider some other important circumstances attending it.
6. After attentively contemplating this spectacle for several nights, the observer will not fail to be struck with the fact, that the relative position and configuration of the objects upon it, remains always unchanged. This remarkable circumstance is rendered the more easily observable by the fact that the objects themselves differ greatly in apparent splendour, some being exceedingly bright and conspicuous, while others are barely distinguishable. The observer soon becomes familiar with the relative arrangement and configuration of the brighter and more conspicuous ones; and, grouping them in his imagination, retains their forms so as immediately to recognise them upon their successive reappearances.
7. This circumstance of the unaltered configuration and relative positions of
this multitude of objects scattered over the firmament, suggests irresistibly
the idea, that the motion of revolution described above, in which they all
participate, is not a motion proper to each separate and independent object, but
one which belongs to the firmament itself, upon which they appear as if they
were fixed. In short, the firmament presents the aspect of a hollow sphere of
vast dimensions, in the centre of which the observer is placed, and upon the
surface of which the countless multitudes of objects which he beholds are fixed.
This stupendous sphere appears to have a motion of revolution on a certain
diameter as an axis, making a complete revolution once in twenty-four hours. The
diameter round which it revolves, or appears to revolve, is directed to a
certain point of the northern quadrant of the meridian, the altitude of which
above the horizon of the observer, will be always found to be exactly equal to
the latitude of his station. This motion of revolution of the firmament,
carrying with it the numerous objects seen upon it, will perfectly explain all
the appearances above described, and many others. Thus, it is evident that all
objects on the celestial sphere must be moved in circles parallel one to another
round its axis; and that these circles become gradually less as the object is
nearer to the pole. When the observer looks to the south, the circles described
by the objects are partly above and partly below the horizon; and, consequently,
all such objects alternately rise and set. But when he looks to the north, the
chief part of the objects which he beholds being nearer to the extremity of the
axis round which the sphere is carried, describe circles smaller and smaller,
which, being entirely above the horizon, the objects in them neither rise nor
8. From what has been stated, it will be obvious, that an object placed precisely at that point of the meridian at which the axis round which the sphere turns terminates, would be immoveable; and would evidently be the only immoveable object in the visible firmament. It does so happen, that there actually is no star precisely at that point; but there is a rather conspicuous one so near to it, that although it moves round it in a small circle, the diameter of which is about six times that of the full moon, such motion can only be ascertained by astronomical instruments; and therefore, for all the purposes of common observation, the star in question may be regarded as stationary, and as indicating the position of the northern extremity of the axis on which the celestial sphere appears to revolve.
This point of the sphere is called its pole; and as there is a corresponding point at the other extremity of the axis, which is [p.150] below the horizon, and therefore invisible, it also receives the name pole, and the two points are distinguished, the visible one as the North Celestial Pole, and the invisible one as the South Celestial Pole.
The motion of the celestial sphere here described is apparent, not real, being merely an optical illusion produced by the diurnal rotation of the earth upon its axis. But this being a point not immediately connected with our present purpose, it will be sufficient here merely to indicate it. The readers who desire to see the explanation of the apparent diurnal motion of the heavens, will find it in the "Museum," vol. iii. pp. 55, 56.
For all the purposes of the observation of the heavens which for the present occupy our exclusive attention, the celestial sphere is to be considered as revolving on its axis once in about twenty-four hours, carrying with it all the objects seen upon it.
9. The objects scattered over this sphere in such vast numbers, differing one from another greatly in their apparent splendour, and being characterised by very various and often remarkable configurations, astronomers have invented a nomenclature to designate them, founded partly on their relative splendour, and partly on their configurations.
A catalogue of the stars being made, in which each star would hold a place determined by its relative splendour, the more splendid having the higher places; if it were required to resolve such a list into classes, according to their decreasing degrees of brightness, it would be impossible to fix upon any points where each succeeding class would end and the next begin; the gradations of brightness, when star is compared with star, being altogether imperceptible. Nevertheless, a distribution according to degrees of relative splendour being by the common consent of astronomers of all ages deemed expedient, such a conventional classification has been adopted, arbitrary as the limits of the succeeding classes must necessarily have been. In this a certain number of the most splendid stars visible in the firmament have received the denomination of stars of the first magnitude; others, of inferior brightness, are called stars of the second magnitude, and so on, the smallest stars visible to the naked eye being classed as stars of the sixth magnitude.
10. The number of stars of each succeeding magnitude increases rapidly as their splendour diminishes. Thus, while there are no more than 18 or 20 of the first magnitude, there are 50 or 60 of the second, about 200 of the third, and so on; the total number visible to the naked eye, up to the sixth magnitude inclusive, being from 5000 to 6000. We shall see on another occasion that this number, great as it is, is no more than an insignificant fraction [p.151] of the total number of stars, the existence of which the telescope discloses to us. But we shall, for the present, limit our observations to the stars which are visible to the naked eye.
It has been stated that the celestial objects generally maintain with relation to each other a certain invariable position, and have no other motion than that imparted to them in common by the sphere to which they are imagined to be attached. To this, however, there is a limited number of exceptions. There is a small number of objects, among which the sun and moon are the most conspicuous, which, while they participate in the diurnal motion of the celestial sphere, are observed continually to shift their position on it, just as if a number of insects were creeping slowly upon the surface of a top while the top is spinning, carrying the insects round with it. These objects, which, exclusive of the sun and moon, are called Planets, have occupied our attention on a former, and will again on a future, occasion; for the present, however, we must be understood to notice only those which maintain invariable relative positions, and which have therefore been denominated fixed stars.
11. The nomenclature of the stars, so far as it is founded upon their apparent relative positions, consists in the resolution of all the stars of the firmament into a certain limited number of groups, called Constellations. These groups have been from ancient times invested with the imaginary forms of men, animals, and various other objects, natural and artificial, and have been named in accordance with these. Thus, the celestial spaces are partitioned out arbitrarily and conventionally into distinct compartments, in a manner somewhat resembling the divisions of the land on the surface of the globe into empires and kingdoms. Each such compartment of the heavens contains a certain number of stars, great and small, the total assemblage of which constitutes the constellation, and is characterised by the proper name conferred upon it.
Since it is of the first necessity that the astronomical student and amateur should be so familiar with this stellar nomenclature as to be able readily to distinguish and recognise not only each principal constellation, but also each principal star in such constellation, we propose here to give such explanations as will present the greatest practicable facilities in the attainment of this object.
The stars composing each constellation are designated by the letters of the Greek alphabet, the first letters being given to the more splendid stars. When the number of stars in a constellation exceeds the number of letters in the Greek alphabet, the letters of the Roman alphabet are used; and when these are exhausted, the [p.152] remaining stars, if any, are expressed by the numbers prefixed to them in the catalogue of Flamstead, generally known as the British Catalogue.
It has been customary among English astronomers to designate the constellations by their Latin names; and the astronomical amateur, besides rendering himself familiar with these, will find it convenient, when he is not a Greek scholar, to make himself acquainted with the characters and names of the letters of the Greek alphabet, which are as follows:
12. To obtain an acquaintance with the several constellations and the stars composing them, so as to be able readily to recognise them on viewing the heavens on a clear night, the student should in the first instance study the form and disposition of one of the most conspicuous of the constellations, and the most suitable for this purpose is that which is called Ursa major, or the great Bear. This constellation is so near the north celestial pole, that in our latitudes it never sets, and is consequently visible at all seasons of the year. It consists of a considerable number of stars, but seven of these, shown in fig. 1, are much more conspicuous than the others, and are consequently the only stars popularly identified [p.153] with the constellation. They are arranged in such a form, that lines connecting them one with another successively would have the shape of a note of interrogation, or of a reaping-hook.
13. In consequence of the proximity of this constellation to the pole, it never
sets in any latitude above that of 40°, and is consequently visible at night in
all seasons of the year in the greater part of the northern hemisphere. This
circumstance, combined with the splendour of the stars composing it and their
remarkable configuration, rendered it an object of universal observation and
attention in the earliest ages; and it may therefore be regarded as one of the
most ancient of the constellations. It is frequently referred to in the Hebrew
Scriptures, and has at various times and in various countries received different
denominations. It is referred to, for example, in the book of Job; but the name
by which it is designated has been mistranslated in the English version by Arcturus, the name of a star in a different constellation. Bochart says that the
Hebrew word in Job is derived from an Arabic one which signifies bier; others
maintain that it signifies a waggon, which would be quite consistent with the
names given to the constellation by various people, ancient and modern, Greeks,
Romans, Italians, Germans, and English, by whom severally it has been named
(Amaxa), waggon or wain; plaustrum, cart; triones, a waggon and oxen;
bier; Cataletto, bier; Wagen, waggon; David's Car, the Plough, and
14. When the constellation was thus named, the four stars marked α β γ and δ were considered to represent the wheels, and the other three stars the shafts, poles, horses or oxen. When the name Bier was applied to it, the four stars forming the quadrangle were considered to represent the sarcophagus, and the three remaining stars were considered to represent three mourners, or, according to some, three children of the deceased. Admiral Smyth quotes Kircher as affirming that the four stars of the quadrangle represent the bier of Lazarus, and that the three remaining stars are Mary, Martha, and Magdalen. He also maintains that the popular name of Charles' Wain is a corruption of the Gothic Karl Wagen, the churl or peasant's cart.
It is a fact worthy of remark, recorded by historians, that the Iroquois, a tribe of North American Indians were found at the moment of the discovery of America to be familiar with the constellation of the Great Bear, which in their language was called Oquoari, the word which signifies bear.
15. Although the only stars of this constellation familiar to the popular eye are the seven principal ones indicated in fig. 1, the group which has received the name of Ursa major included from [p.154] the earliest times many others of inferior, splendour, and this number has been gradually augmented as the range and accuracy of observations have been increased by the improvement of telescopes. From the era of Ptolemy, A.D. 150, to that of Copernicus, A.D. 1500, this constellation contained 35 stars. In the time of Kepler, A.D. 1600, the number was augmented to 56. In Flamstead's Catalogue, A.D. 1700, the number was further augmented to 87, and, in fine, at the beginning of the present century, it was increased to 338.
The constellation, including the stars composing it so far as they are visible without a telescope, is shown in fig. 2, p. 145, where the position and form of the imaginary figure of the bear relatively to the stars are indicated. It will be seen that the four stars α β γ and δ are upon the side, the three others marking the tail.
16. It will be observed in fig. 2 that the principal stars of the constellation, besides being indicated by the Greek letters, are also designated by certain proper names, mostly of Arabic or Oriental origin; and it may here be stated in general that besides the method of designating stars by naming the constellation to which they belong, and the letter which distinguishes them in such constellation, most of the conspicuous stars have received proper names which probably were conferred upon them before the system of constellations was established; and many of these stars are now much more frequently designated by these proper names than by that which connects them with the constellation. Thus, for example, the most splendid star in the constellation of Canis major or the greater Dog, instead of being called a Canis majoris, which would be its name in the nomenclature of the constellations, is almost invariably called Sirius. In the same manner, the principal star of the constellation Leo, is always called Regulus and never α Leonis.
These observations, however, are not applicable in the same manner to the seven principal stars of Ursa major, which are more generally designated by the Greek letters which connect them with the constellation.
17. The position of the stars composing a constellation is also frequently indicated by naming the part of the imaginary figure designating the constellation at which the star is found. Thus, for example, the position of η Ursæ majoris, is indicated by stating that it is at the tip of the tail. In like manner, the position of a certain star in the constellation Taurus, is indicated by stating that it is in the "bull's eye." This form of expression, which is in very frequent use with astronomers, seems to render it unadvisable to efface altogether from maps of the stars the figures designating the constellations, as is sometimes done.
Although the proper names of the principal stars of Ursa major are not now in
general use, they ought not on that account
to be altogether overlooked or neglected, since they are often the means of
identifying these objects with those indicated in ancient historical records.
Close to the star Mizar, in the tail of the Great Bear, is a small star called Alcor, which Humboldt says the Arabs called "saidak," which signifies trial or test, since they used it as a test of the sharpness of the sight of the observer.
18. If a straight line be imagined to be drawn from the star β to α, and continued beyond α to a distance equal to five times the distance between α and β, or, what is nearly the same, to the whole distance between α and η, it will arrive at the principal star of a smaller constellation called Ursa minor or the lesser Bear. This is the star already mentioned as being within a degree and a half of the pole, and which, being generally adopted as the easiest practical means of marking that important point, is called the Pole star. The other stars of the constellation of Ursa minor have nearly the same configuration as those of Ursa major; but the position of the figure is reversed, the tail, at the tip of which the pole star is placed, corresponding with the head of Ursa major.
The important service thus performed by the stars α and β Ursæ majoris, in indicating by their direction the position of the pole star, has given them the name of the Pointers; they are also sometimes called the Guards.
This method of ascertaining the position of the principal star and the constellation generally of Ursa minor, by means of the more conspicuous and better known constellation of Ursa major, has been generalised with the greatest benefit to astronomical students and amateurs by extending the method of pointers, so as to trace one constellation from another throughout the entire firmament, as will presently appear.
19. The constellation of Ursa minor being so placed that the principal star, at the tip of the bear's tail, is close to the pole, the diurnal motion of the sphere causes the figure of the bear to swing round the pole feet foremost, as if its tail were nailed to that point. The four successive positions of the constellation at intervals of six hours, are shown in fig. 3, p. 161.
The star β of this constellation, situate on the head of the bear, and therefore more distant from the pole, is easily seen to revolve round the pole as a centre, so that this constellation was regarded as a great celestial clock, and before the advancement of science furnished mariners with other and better means, it was of great use in navigation.
The constellation of the Great Bear being in the quarter of the heavens opposite
to that in which the sun is found in the beginning of September, it will be seen
on the meridian not far south of the zenith at that season in these latitudes,
It will, on the contrary, be on the meridian a little above the horizon at midnight, in the beginning of March. The most favourable times, therefore, for observations upon it, are the months of summer and autumn.
20. A circle described round the north celestial pole, including within it a certain extent of the heavens is called the Arctic circle, from the Greek word Αρκτος, "arktos," signifying a bear, that being, as it were, the region of the bears.
21. To extend the method of pointers to the discovery of the position of other constellations, let us suppose a line carried from the star δ of Ursa major to the pole star, and continued beyond the pole star to an equal distance; this line will then arrive at a well-known constellation called Cassiopeia's chair. This constellation consists of several stars, six of which being the most conspicuous are shown in fig. 4. Four of these α β κ and γ, formed the legs and seat, and the two others δ and ε the back.
If the line drawn from α of Ursa major through the pole star be continued beyond
the latter nearly in a direct line, it will
arrive at a constellation called Pegasus, which will be easily recognised by
four brilliant stars forming a quadrangle very
similar to that already described in the constellation of Ursa major. This
quadrangle with its position relatively to the pole star, and the line
proceeding through that star from the pointers is shown in fig. 5.
22. Of these four stars, three only properly belong to the constellation called Pegasus; these three being β α, and γ, forming the upper right hand corner of the quadrangle. The fourth star, marked also α, belongs to an adjacent constellation called Andro- [p.157] meda, three of the principal stars of which, marked α, β, and γ, are shown in the figure. By continuing the line of these stars slightly curved, we arrive at another conspicuous star about as far from γ as γ itself is from β. This last is the principal star α of the constellation called Perseus.
23. The seven bright stars, here described, three of which belong to the
constellation Pegasus; three others to Andromeda,
and the fourth to Perseus, have a configuration strikingly similar to that of
the seven principal stars of Ursa major, as will be easily perceived by fig. 4.
A second bright star, belonging also to the constellation of Perseus, familiarly known in stellar astronomy by the name of Algol, is also shown in the figure; it makes a right angle with the other star α of Perseus, and the star γ of Andromeda.
24. If a line be drawn from the star γ of Pegasus, through the star γ of Andromeda, and continued to an equal distance beyond the latter, it will arrive at a splendid star of the first magnitude called Capella, being the principal star of the constellation called Auriga. This star, and its relative position to the others, is also shown in the figure.
25. A general view of the stars included within the region of the firmament
which we have now traced is exhibited in fig. 6,
so as to enable the student to perceive at a single view all the stars which
have been just indicated. Six of the principal stars of Ursa major appear at the
upper right hand angle of the figure, [p.158] and lines are drawn in various directions connecting the principal stars, to
show the student the manner of tracing the position of those which he seeks,
from those which he already knows. It is
assumed that he is already so familiar with the principal stars of Ursa major
and the pole star, that he can at once distinguish them. Besides the connecting
lines already mentioned, he will see that the position of Algol can be
ascertained by a straight line drawn from the star
η of Ursa major, and
continued to nearly an [p.159] equal distance beyond the pole star. The star Capella can also be found by
following the direction of a line through γ and
α of Ursa major, as shown in the
figure. If a line be imagined to be drawn through γ and
α of Ursa major, and
continued onwards to a distance from δ equal to the distance between the pole
star and Pegasus, it will arrive at the principal star of the constellation Lyra,
called Vega; and, if a line be drawn from this star at right angles to the
former, it will arrive at the principal star of the constellation of Cygnus,
generally known as a Cygni, but also called Adrided.
If a line be drawn through the stars α of Andromeda and β of Pegasus, and be continued through the latter to a distance equal to about four times the distance between these stars, it will arrive at another conspicuous star of the first magnitude, shown in the figure, called Altair, being the principal star of the constellation Aquila or the Eagle.
26. The most magnificent constellation of the firmament, surpassing not only in
splendour, but in the almost countless number
of its component stars, profusely sprinkled also with nebulae, as will hereafter
appear, is Orion, the principal stars of
which are shown in fig. 7, and will be immediately recognised by every eye
familiar with the appearance of the firmament.
This splendid stellar combination, lying across that part of the ecliptic over
which the sun passes in December, will
always be visible about midnight on the southern meridian in the month of June,
and may indeed be viewed with great advantage and facility during the summer and
the latter part of spring. The principal stars, when connected by imaginary
form a figure resembling that of an hour-glass. The figure from which the
constellation takes its name is a mythological personage, celebrated as a giant
and a hunter, who after his death was, according to Homer, elevated to the stars
(Iliad, lib. xviii. 486 ; xxii. 29; Od. [p.160] v. 274,) where he is represented as a giant, with a girdle or belt, a sword, a
cloak of lion skin, and a club.
The stars marked α and γ in the figure, are in the shoulders, and those marked κ and β, in the feet. The three central stars, δ ε ξ form the belt.
Manilius, quoted by Admiral Smyth, says of this constellation:
"Orion's beams! Orion's beams!
His star-gemmed belt and shining blade,
His isles of light, his silvery streams,
And gloomy gulfs of mystic shade."
No constellation, continues Admiral Smyth, was more noted among the ancients than this. As it occupies an extensive space in the heavens, this circumstance may have probably given Pindar his notion that Orion was of a monstrous size, and hence the "jugula" of Plautus, the "Magni pars maxima coeli" of Manilius, and the "jebber" of the Arabians. When the rage for innovation was more prevalent than at present, it was proposed to invest this constellation with the figure and to confer upon it the name of Nelson; and in 1807, when Napoleon was in the meridian of his power, the University of Leipzic passed a resolution that the stars of the belt and sword should be erected into an independent constellation to be called Napoleon.
Fig. 3. THE DIURNAL REVOLUTION OR THE CONSTELLATION OF THE LESSER BEAR.
27. Antiquity of the name of Orion. 28. Nebulæ in the constellation Orion. 29.
General view of this region of the heavens. 30. Procyon and Sirius. 31.
Aldebaran: the Hyades and the Pleiades. 32. The constellations of the zodiac.
33. Use of celestial maps. 34. Use of a celestial globe. 35. To find the place
of an object in the heavens.
27. THE name of Orion is of high antiquity, occurring in the books of Job, Amos, Ezekiel, and Isaiah. Some commentators contend, however, that the personage figured in the constellation is no other than Nimrod. It was believed that when this constellation was in such a position as to precede the sun in rising, storms and rain ensued, and Orion is hence characterised by such epithets as "Imbrifer," (the bringer of rain;) "Nimbosus," (the cloudy;) and "Aquosus," (the watery). The Latin poets overflow [p.162] with invectives against the pluviosus et tristis Orion; with Horace, he is the "nautis infestus;" with Propertius, the "aquosus;" and with Pliny, the "horridus sideribus."
Two of the four principal stars, those marked α and β in the figure, are of the first magnitude, the former being generally called by the proper name, Betelgeux, and the latter, Rigel.
The three stars forming the belt are of the second magnitude, and have been popularly known by different names, such, as "Jacob's staff," the "yard wand," and the "three kings."
28. The star marked θ in the figure, situate midway between the three stars of the belt and the two stars of the feet, proves to be a very remarkable object when submitted to examination with adequate telescopic power. It is not one, but five stars, combined in close juxtaposition; and is moreover surrounded by one of the most remarkable nebulæ in the firmament. These are points, however, which do not fall within the limits of this Tract, but to which we will return on another occasion.
29. To present to the student a collective view of the conspicuous stars and constellations which have been above described, we have given, in fig. 8, a view of a portion of the firmament within which they are included. If the student imagine himself directing his view to the heavens, with his face to the north, on any night about the middle of June, at or near the hour of midnight, he will see above him the stars and constellations indicated in the upper half of the figure; and, if he turn with his face to the south, he will see those included in the lower half. Immediately above his head, and close to the zenith, he will see the splendid star Capella; if he carry his eye from the pole star through Capella, towards the south, he will recognise at once the constellation of Orion, which we have just described. The centre star of the belt will be due south. The bright star Betelgeux will be to the right, and Rigel to the left of the meridian; that is, the former will be west and the latter east of the meridian. If he carry his eye in a direct line from the stars ε and δ of Ursa major, he will arrive at the bright star Pollux in the constellation Gemini, and beside it will see the still brighter star Castor, of the same constellation, the latter being of the first, and the former of the second, magnitude.
30. If the same line, directed from the stars of Ursa major through Pollux, be continued nearly in the same direction, it will arrive at Procyon, a star of the first magnitude in the constellation of Canis minor.
If an equilateral triangle be imagined to be formed upon the south side of the line joining Procyon with Betelgeux, its vertex will fall upon Sirius, a star of the first magnitude and the [p.163]
Fig. 8 GENERAL VIEW OF THE REGION AROUND THE STAR CAPELLA,
INCLUDING THE CONSTELLATION OF ORION.
[p.164] brightest in the firmament, being the principal star of the constellation of
Canis major, and thence often called the Dog Star. Indeed, this star, from its
extraordinary splendour, will be recognised at once by the eye, without the
necessity of tracing its position by pointers.
31. If a line be imagined to be drawn from Sirius to the star γ, called Bellatrix, in the shoulder of Orion, and continued beyond that point to about half the distance between these stars, it will arrive at a conspicuous star of the first magnitude, called Aldebaran, in the constellation of Taurus. This star is placed in the southern eye of the bull, and the three stars of Orion's belt may be considered also as pointers to it.
The constellation of Taurus, of which Aldebaran is the principal star, is remarkable for two splendid clusters visible to the naked eye, and which, being known to the ancients, were called the Hyades and the Pleiades; the former group is in immediate juxtaposition with the eye of the bull, and the latter is in its neck. The mythological origin of these constellations is, as commonly given, as follows: The Hyades were the daughters of Atlas and Pleione, whose brother Hyas being torn to pieces by a bull, they were overwhelmed with grief, and are said to have wept so incessantly, that the gods in compassion took them into heaven and placed them near the bull's eye, where they still continue to weep; and, accordingly, it was a popular superstition that when they rise immediately before the sun, wet weather ensues. Indeed, the name Hyades is derived immediately from a Greek word ϒαδες, (Hyades), which signifies the "rainers."
The Pleiades, also daughters of Atlas and Pleione, and therefore sisters of the
Hyades, were seven in number; six being visible and the seventh invisible. The
seventh was called Sterope, and it was related that she became invisible
because, while her sisters had all consorted themselves with gods, she alone
yielded to Sisyphus, a mortal. According to other traditions, the seventh Pleiad
was called Electra, and her disappearance was explained by her grief at the
destruction of the house of Dardanus. The Pleiades are said to have destroyed
themselves from grief at the death of their sisters the Hyades. They were
afterwards placed among the stars, where they formed a cluster resembling a
bunch of grapes, whence they were sometimes called
Βοτρυς (Botrus). The rising
of these stars before the sun, like that of the Hyades, was considered to
If the line of the pointers drawn to the pole star be a little deflected to the left and continued onwards, it will arrive at a remarkable star of the first magnitude, shown in the figure, called α Cygni, being the principal star in the constellation of Cygnus. [p.165] This star is sometimes called Adrided; it was called by the Arabians Deneb.
32. Every one is familiar with the fact that, in the course of a year, the sun appears to move round a great circle of the heavens called the Ecliptic, and in so doing passes through a series of constellations which lie in that route. The stars composing these are generally included within a zone extending to 10° or 12° on each side of the ecliptic. This zone is called the Zodiac, from the Greek word Ζωδιον (Zodion), which signifies a small painted or carved figure of an animal, the zodiac being filled with a series of constellations, to which the names and forms of animals were given. The twelve well-known zodiacal constellations are:
|1. Aries (the ram) .....||^||7. Libra (the balance) ....||d|
|2. Taurus (the bull) ....||_||8. Scorpio (the scorpion) ....||e|
|3. Gemini (the twins) ....||`||9. Sagittarius (the archer) ....||f|
|4. Cancer (the crab) ....||a||10. Capricorn us (the goat) ....||g|
|5. Leo (the lion) ....||b||11. Aquarius (the waterman) ...||h|
|6. Virgo (the virgin) ....||c||12. Pisces (the fishes) ....||i|
The signs here annexed to the names are abridged means of expressing not the
constellations, but the successive divisions of
the ecliptic to which the constellation corresponded at the time they received
their names. It must here be explained, that by a peculiar change which has
taken place in the annual path of the sun through the heavens, that luminary
does not now follow precisely the same course which it followed in remote ages.
The position of the sun on the day of the equinox is subject to a small change
from year to year, which, though insignificant in short intervals of time,
becomes very considerable when it accumulates for ages. Thus, when the
constellations of the zodiac received their names, the sun entered the
constellation Aries on the day of the spring equinox; but, owing to the cause
just explained, the moment at which it entered that constellation became from
year to year later and later, until, after the lapse of many centuries, it did
not enter Aries till a month after the day of the equinox. During the first
month after the equinox the sun is therefore at
present in the constellation of Pisces, and not in that of Aries.
As there were twelve zodiacal constellations, the ecliptic in which the sun revolves was divided into twelve equal arcs of 30° each, which were called signs, the first 30° commencing from its position on the day of the equinox, was called the sign Aries, the second Taurus, and so on. And although, owing to the change of position of the ecliptic already indicated, the positions of the constellations from which these signs have taken their names have changed so that, in fact, the constellation Pisces is [p.166] found in the first sign, and Aries in the second, and so on; the signs have, nevertheless, retained their names.
It is therefore important that the astronomical amateur should not confound the name of the sign with the name of the constellation. The sign Aries is the first 30° of the ecliptic, while the constellation Aries is a group of stars, at present situate between the 30th degree and 60th degree of the ecliptic.
The ancients recognised, besides the twelve zodiacal constellations, twenty-one constellations in the northern, and fifteen in the southern hemisphere. The progress of stellar discovery has, however, augmented considerably these somewhat arbitrary groups of stars, and the number of constellations now recognised amounts to 117, of which 62 are in the northern hemisphere.
33. From all that has been explained above, the student will be able to appreciate the benefit to be derived from having in his possession a collection of celestial maps. Many such have been published, among which may be mentioned more particularly those prepared under the superintendence of the Society for the Diffusion of Useful Knowledge. I have found, however, one of the most convenient for general purposes, "The Guide to the Stars."* In the maps there given, will be found indications of the most useful applications of the method of pointing.
34. A celestial globe may be defined to be a working model of the heavens. It is mounted like a common terrestrial globe. The visible hemisphere is bounded by the horizontal circle in which the globe rests. The brass circle at right angles to this, is the celestial meridian. The constellations, with outlines of the imaginary figures from which they take their names, are delineated upon it.
The globe will serve, not merely as an instrument of instruction, but will prove a ready and convenient aid to the amateur in astronomy, superseding the necessity of many calculations which are often discouraging and repulsive, however simple and easy they may be to those who are accustomed to such inquiries. Most of the almanacs contain tables of the principal astronomical phenomena, of the places of the sun and moon, and of the principal planets as well as the times when the most conspicuous stars are on the meridian after sunset. These data, together with a judicious use of the globe and a tolerable telescope, will enable any person to extend .his acquaintance with astronomy, and even to become a useful contributor to the common stock of information which is now so fast increasing by the zeal and ability of private observers in so many quarters of the globe.
To prepare the globe for use, let small marks (bits of paper gummed on will
answer the purpose) be placed upon it, to indicate the positions of the sun,
moon, and planets, at the time of observing the heavens. The place of the sun on
the ecliptic is usually marked on the globe itself. If not, its right ascension
(that is, its distance from the vernal equinoxial point, measured on the
celestial equator), and its declination (that is, its distance north or south of
the equator), are given in the almanac, for every day. The moon's right
ascension and declination are likewise given.
35. To find the place of an object on the globe when its right ascension and declination are known. Find the point on the equator where the given right ascension is marked. Turn the globe on its axis till this point be brought under the meridian. Then count off an arc of the meridian (north or south of the equator, according as the declination is given) of a length equal to the given declination, and the point of the globe immediately under the point of the meridian thus found, will be the place of the object. By this rule, the position on the globe of any object of which the right ascension and declination are known, may be immediately found, and a corresponding mark put upon it.
To adjust the globe so as to use it as a guide to the position of objects on the heavens, and as a means of identifying the stars and learning their names, let the lower clamping-screw of the meridian be loosened, and let the north pole of the globe be elevated by moving the brass meridian until the arc of this meridian between the pole and the horizon be equal to the latitude of the place of observation. Let the clamping-screw be then tightened, so as to maintain the meridian in this position. Let the globe be then so placed that the brass meridian shall be directed due north and south, the pole being turned to the north. This being done, the globe will correspond with the heavens so far as relates to the poles, the meridian, and the points of the horizon.
To ascertain the aspect of the firmament at any hour of the night, it is now only necessary to turn the globe upon its axis until the mark indicating the place of the sun shall be under the horizon in the same position as the sun itself actually is at the hour in question. To effect this, let the globe be turned until the mark indicating the position of the sun is brought under the meridian. Observe the hour marked on the point of the equator which is then under the meridian. Add to this hour the hour at which the observation is about to be taken, and turn the globe until the point of the equator on which is marked the hour resulting from this addition is brought under the meridian. The position of the globe will then correspond with that of the firmament. Every object on [p.168] the one will correspond in its position with its representative mark or symbol on the other. If we imagine a line drawn from the centre of the globe through the mark upon its surface indicating any star, such a line, if continued outside the surface toward the heavens, would be directed to the star itself.
For example, suppose that when the mark of the sun is brought under the meridian, the hour 5h. 40m. is found to be on the equator at the meridian, and it is required to find the aspect of the heavens at half-past ten o'clock in the evening.
Let the globe be turned until 16h. 10m. is brought under the meridian, and the aspect given by it will be that of the heavens.
* Twelve Planispheres, forming a Guide to the Stars for every Night in the Year, with an Introduction. Taylor and Walton, London.