THE STARRY HEAVENS

We now leave the bounds of our own system, and pass outwards towards the almost infinite spaces and multitudes of the fixed stars. In doing so we are at once confronted with a wealth and profusion of beauty and a vastness of scale which are almost overwhelming. Hitherto we have been dealing almost exclusively with bodies which, though sometimes considerably larger than our world, were yet, with the exception of the sun, of the same class and comparable with it; and with distances which, though very great indeed, were still not absolutely beyond the power of apprehension. But now all former scales and standards have to be left behind, for even the vast orbit of Neptune, 5,600,000,000 of miles in diameter, shrinks into a point when compared with the smallest of the stellar distances. Even our unit of measurement has to be changed, for miles, though counted in hundreds of millions, are inadequate; and, accordingly, the unit in which our distance from the stars is expressed is the 'light year,' or the distance travelled by a ray of light in a year.

Light travels at the rate of about 186,000 miles a second, and therefore leaps the great gulf between our earth and the sun in about eight minutes. But even the nearest of the fixed stars—Alpha Centauri, a star of the first magnitude in the Southern Hemisphere—is so incredibly distant that light takes four years and four months to travel to us from it; while the next nearest, a small star in Ursa Major, is about seven light-years distant, and the star 61 of the constellation Cygnus, the first northern star whose distance was measured, is separated from us by two years more still.

At present the distances of about 100 stars are known approximately; but it must be remembered that the approximation is a somewhat rough one. The late Mr. Cowper Ranyard once remarked of measures of star-distances that they would be considered rough by a cook who was in the habit of measuring her salt by the cupful and her pepper by the pinch. And the remark has some truth—not because of any carelessness in the measurements, for they are the results of the most minute and scrupulous work with the most refined instrumental means that modern skill can devise and construct—but because the quantities to be measured are almost infinitely small.

It is at present considered that the average distance from the earth of stars of the first magnitude is thirty-three light years, that of stars of the second fifty-two, and of the third eighty-two. In other words, when we look at such stars on any particular evening, we are seeing them, not as they are at the moment of observation, but as they were thirty-three, fifty-two, or eighty-two years ago, when the rays of light which render them visible to us started on their almost inconceivable journey. The fact of the average distance of first-magnitude stars being less than that of second, and that of second in turn less than that of third, is not to be held as implying that there are not comparatively small stars nearer to us than some very bright ones. Several insignificant stars are considerably nearer to us than some of the most brilliant objects in the heavens—e.g., 61 Cygni, which is of magnitude 4·8, is almost infinitely nearer to us than the very brilliant first magnitude star Rigel in Orion. The rule holds only on the average.

The number of the stars is not less amazing than their distance. It is true that the number visible to the unaided eye is not by any means so great as might be imagined on a casual survey. On a clear night the eye receives the impression that the multitude of stars is so great as to be utterly beyond counting; but this is not the case. The naked-eye, or 'lucid,' stars have frequently been counted, and it has been found that the number visible to a good average eye in both hemispheres together is about 6,000. This would give for each hemisphere 3,000, and making allowance for those lost to sight in the denser air near the horizon, or invisible by reason of restricted horizon, it is probable that the number of stars visible at any one time to any single observer in either hemisphere does not exceed 2,500. In fact Pickering estimates the total number visible, down to and including the sixth magnitude, to be only 2,509 for the Northern Hemisphere, and on that basis it may safely be assumed that 2,000 would be the extreme limit for the average eye.

But this somewhat disappointing result is more than atoned for when the telescope is called in and the true richness of the heavenly host begins to appear. Let us take for illustration a familiar group of stars—the Pleiades. The number of stars visible to an ordinary eye in this little group is six; keen-sighted people see eleven, or even fourteen. A small telescope converts the Pleiades into a brilliant array of luminous points to be counted not by units but by scores, while the plates taken with a modern photographic telescope of 13 inches aperture show 2,326 stars. The Pleiades, of course, are a somewhat notable group; but those who have seen any of the beautiful photographs of the heavens, now so common, will know that in many parts of the sky even this great increase in number is considerably exceeded; and that for every star the eye sees in such regions a moderate telescope will show 1,000, and a great instrument perhaps 10,000. It is extremely probable that the number of stars visible with the largest telescopes at present in use would not be overstated at 100,000,000 (Plate XXVII.).

It is evident, on the most casual glance at the sky, that in the words of Scripture, 'One star differeth from another star in glory.' There are stars of every degree of brilliancy, from the sparkling white lustre of Sirius or Vega, down to the dim glimmer of those stars which are just on the edge of visibility, and are blotted out by the faintest wisp of haze. Accordingly, the stars have been divided into 'magnitudes' in terms of scales which, though arbitrary, are yet found to be of general convenience. Stars of the first six magnitudes come under the title of 'lucid' stars; below the sixth we come to the telescopic stars, none of which are visible to the naked eye, and which range down to the very last degree of faintness. Of stars of the first magnitude there are recognised about twenty, more or less. By far the brightest star visible to us in the Northern Hemisphere, though it is really below the Equator, is Sirius, whose brightness exceeds by no fewer than fourteen and a half times that of Regulus, the twentieth star on the list. The next brightest stars, Canopus and Alpha Centauri, are also Southern stars, and are not visible to us in middle latitudes. The three brightest of our truly Northern stars, Vega, Capella, and Arcturus, come immediately after Alpha Centauri, and opinions are much divided as to their relative brightness, their diversity in colour and in situation rendering a comparison somewhat difficult. The other conspicuous stars of the first magnitude visible in our latitudes are, in order of brightness, Rigel, Procyon, Altair, Betelgeux, Aldebaran, Pollux, Spica Virginis, Antares, Fomalhaut, Arided (Alpha Cygni), and Regulus, the well-known double star Castor following not far behind Regulus. The second magnitude embraces, according to Argelander, 65 stars; the third, 190; fourth, 425; fifth, 1,100; sixth, 3,200; while for the ninth magnitude the number leaps up to 142,000. It is thus seen that the number of stars increases with enormous rapidity as the smaller magnitudes come into question, and, according to Newcomb, there is no evidence of any falling off in the ratio of increase up to the tenth magnitude. In the smaller magnitudes, however, the ratio of increase does not maintain itself. The number of the stars, though very great, is not infinite.

A further fact which quickly becomes apparent to the naked eye is that the stars are not all of the same colour. Sirius, for example, is of a brilliant white, with a steely glitter; Betelgeux, comparatively near to it in the sky, is of a beautiful topaz tint, perhaps on the whole the most exquisite single star in the sky, so far as regards colour; Aldebaran is orange-yellow, while Vega is white with a bluish cast, as is also Rigel. These diversities become much more apparent when the telescope is employed. At the same time the observer may be warned against expecting too much in the way of colour, for, as a matter of fact, the colours of the stars, while perfectly manifest, are yet of great delicacy, and it is difficult to describe them in ordinary terms without some suspicion of exaggeration. Stars of a reddish tone, which ranges from the merest shade of orange-yellow up to a fairly deep orange, are not uncommon; several first-magnitude stars, as already noted, have distinct orange tones. For anything approaching to real blues and greens, we must go to the smaller stars, and the finest examples of blue or green stars are found in the smaller members of some of the double systems. Thus in the case of the double Beta Cygni (Albireo), one of the most beautiful and easy telescopic objects in the northern sky, the larger star is orange-yellow, and the smaller blue; in that of Gamma AndromedÆ the larger is yellow, and the smaller bluish-green; while Gamma Leonis has a large yellow star, and a small greenish-yellow one in connection. The student who desires to pursue the subject of star colours should possess himself of the catalogue published in the Memoirs of the British Astronomical Association, which gives the colours of the lucid stars determined from the mean of a very large number of observations made by different observers.

In this connection it may be noticed that there is some suspicion that the colours of certain stars have changed within historic times, or at least that they have not the same colour now which they are said to have had in former days. The evidence is not in any instance strong enough to warrant the assertion that actual change has taken place; but it is perfectly natural to suppose that it does, and indeed must gradually progress. As the stars are intensely hot bodies, there must have been periods when their heat was gradually rising to its maximum, and there must be periods when they will gradually cool off to extinction, and these stages must be represented by changes in the colour of the particular star in question. In all probability, then, the colour of a star gives some indication of the stage to which it has advanced in its life-history; and as a matter of fact, this proves to be so, the colour of a star being found to be generally a fair indication of what its constitution, as revealed by the spectroscope, will be.

Another feature of the stars which cannot fail to be noticed is the fact that they are not evenly distributed over the heavens, but are grouped into a variety of configurations or constellations. In the very dawn of human history these configurations woke the imaginations of the earliest star-gazers, and fanciful shapes and titles were attached to the star-groups, which have been handed down to the present time, and are still in use. It must be confessed that in some cases it takes a very lively imagination to find any resemblance between the constellation and the figure which has been associated with it. The anatomy of Pegasus, for example, would scarcely commend itself to a horse-breeder, while the student will look in vain for any resemblance to a human figure, heroic or unheroic, in the straggling group of stars which bears the name of Hercules. At the same time a few of the constellations do more or less resemble the objects from which their titles are derived. Thus the figure of a man may without any great difficulty be traced among the brilliant stars which form the beautiful constellation Orion; while Delphinus presents at least an approximation to a fish-like form, and Corona Borealis gives the half of a diadem of sparkling jewels.

A knowledge of the constellations, and, if possible, of the curious old myths and legends attaching to them, should form part of the equipment of every educated person; yet very few people can tell one group from another, much less say what constellations are visible at a given hour at any particular season of the year. People who are content merely to gape at the heavens in 'a wonderful clear night of stars' little know how much interest they are losing. When the constellations and the chief stars are learned and kept in memory, the face of the sky becomes instinct with interest, and each successive season brings with it the return of some familiar group which is hailed as one hails an old friend. Nor is the task of becoming familiar with the constellations one of any difficulty. Indeed, there are few pleasanter tasks than to trace out the figures of the old heroes and heroines of mythology by the help of a simple star-map, and once learned, they need never be forgotten. In this branch of the subject there are many easily accessible helps. For a simple guide, Peck's 'Constellations and how to Find Them' is both cheap and useful, while Newcomb's 'Astronomy for Everybody' and Maunder's 'Astronomy without a Telescope' also give careful and simple directions. Maunder's volume is particularly useful for a beginner, combining, as it does, most careful instructions as to the tracing of the constellations with a set of clear and simple star-charts, and a most interesting discussion of the origin of these ancient star-groups. A list of the northern constellations with a few of the most notable objects of interest in each will be found in Appendix II.

Winding among the constellations, and forming a gigantic belt round the whole star-sphere, lies that most wonderful feature of the heavens familiar to all under the name of the Milky Way. This great luminous girdle of the sky may be seen in some portion of its extent, and at some hour of the night, at all seasons of the year, though in May it is somewhat inconveniently placed for observation. Roughly speaking, it presents the appearance of a broad arch or pathway of misty light, 'whose groundwork is of stars'; but the slightest attention will reveal the fact that in reality its structure is of great complexity. It throws out streamers on either side and at all angles, condenses at various points into cloudy masses of much greater brilliancy than the average, strangely pierced sometimes by dark gaps through which we seem to look into infinite and almost tenantless space (Plate XXVII.), while in other quarters it spreads away in considerable width, and to such a degree of faintness that the eye can scarcely tell where it ends. At a point in the constellation Cygnus, well seen during autumn and the early months of winter, it splits up into two great branches which run separate to the Southern horizon with a well-marked dark gap dividing them.

When examined with any telescopic power, the Milky Way reveals itself as a wonderful collection of stars and star-clusters; and it will also be found that there is a very remarkable tendency among the stars to gather in the neighbourhood of this great starry belt. So much is this case that, in the words of Professor Newcomb, 'Were the cloud-forms which make up the Milky Way invisible to us, we should still be able to mark out its course by the crowding of the lucid stars towards it.' Not less remarkable is the fact that the distribution of the nebulÆ with regard to the Galaxy is precisely the opposite of that of the stars. There are, of course, many nebulÆ in the Galaxy; but, at the same time, they are comparatively less numerous along its course, and grow more and more numerous in proportion as we depart from it. It seems impossible to avoid the conclusion that these twin facts are intimately related to one another, though the explanation of them is not yet forthcoming.

In the year 1665 the famous astronomer Hooke wrote concerning the small star Gamma Arietis: 'I took notice that it consisted of two small stars very near together; a like instance of which I have not else met with in all the heavens.' This is the first English record of the observation of a double star, though Riccioli detected the duplicity of Zeta UrsÆ Majoris (Mizar), in 1650, and Huygens saw three stars in Theta Orionis in 1656. These were the earliest beginnings of double-star observation, which has since grown to such proportions that double stars are now numbered in the heavens by thousands. Of course, certain stars appear to be double even when viewed with the unaided eye. Thus Mizar, a bright star in the handle of the Plough, referred to above, has not far from it a fainter companion known as Alcor, which the Arabs used to consider a test of vision. Either it has brightened in modern times, or else the Arabs have received too much credit for keenness of sight, for Mizar and Alcor now make a pair that is quite easy to very ordinary sight even in our turbid atmosphere. Alpha Capricorni, and Zeta Ceti, with Iota Orionis are also instances of naked-eye doubles, while exceptionally keen sight will detect that the star Epsilon LyrÆ, which forms a little triangle with the brilliant Vega and Zeta LyrÆ, is double, or at least that it is not single, but slightly elongated in form. Astronomers, however, would not call such objects as these 'double stars' at all; they reserve that title for stars which are very much closer together than the components of a naked-eye double can ever be. The last-mentioned star, Epsilon LyrÆ, affords a very good example of the distinction. To the naked eye it is, generally speaking, not to be distinguished from a single star. Keen sight elongates it; exceptionally keen sight divides it into two stars extremely close to one another. But on using even a very moderate telescope, say a 2½-inch with a power of 100 or upwards, the two stars which the keenest sight could barely separate are seen widely apart in the field, while each of them has in its turn split up into two little dots of light. Thus, to the telescope, Epsilon LyrÆ is really a quadruple star, while in addition there is a faint star forming a triangle with the two pairs, and a large instrument will reveal two very faint stars, the 'debilissima,' one on either side of the line joining the larger stars. These I have seen with 3?-inch.

What the telescope does with Epsilon LyrÆ, it does with a great multitude of other stars. There are thousands of doubles of all degrees of easiness and difficulty—doubles wide apart, and doubles so close that only the finest telescopes in the world can separate them; doubles of every degree of likeness or of disparity in their components, from Alpha Geminorum (Castor), with its two beautiful stars of almost equal lustre, to Sirius, where the chief star is the brightest in all the heavens, and the companion so small, or rather so faint, that it takes a very fine glass to pick it out in the glare of its great primary. The student will find in these double stars an extremely good series of tests for the quality of his telescope. They are, further, generally objects of great beauty, being often characterized, as already mentioned, by diversity of colour in the two components. Thus, in addition to the examples given above, Eta CassiopeiÆ presents the beautiful picture of a yellow star in conjunction with a red one, while Epsilon BoÖtis has been described as 'most beautiful yellow and superb blue,' and Alpha Herculis consists of an orange star close to one which is emerald green. It has been suggested that the colours in such instances are merely complementary, the impression of orange or yellow in the one star producing a purely subjective impression of blue or green when the other is viewed; but it has been conclusively proved that the colours of very many of the smaller stars in such cases are actual and inherent.

Not only are there thousands of double stars in the heavens, but there are also many multiple stars, where the telescope splits an apparently single star up into three, four, or sometimes six or seven separate stars. Of these multiples, one of the best known is Theta Orionis. It is the middle star of the sword which hangs from the belt of Orion, and is, of course, notable from its connection with the Great Nebula; but it is also a very beautiful multiple star. A 2½-inch telescope will show that it consists of four stars in the form of a trapezium; large instruments show two excessively faint stars in addition. Again, in the same constellation lies Sigma Orionis, immediately below the lowermost star of the giant's belt. In a 3-inch telescope this star splits up into a beautiful multiple of six components, their differences in size and tint making the little group a charming object.

Looking at the multitude of double and multiple stars, the question can scarcely fail to suggest itself: Is there any real connection between the stars which thus appear so close to one another? It can be readily understood that the mere fact of their appearing close together in the field of the telescope does not necessarily imply real closeness. Two gas-lamps, for instance, may appear quite close together to an observer who is at some distance from them, when in reality they may be widely separated one from the other—the apparent closeness being due to the fact that they are almost in the same line of sight. No doubt many of the stars which appear double in the telescope are of this class—'optical doubles,' as they are called, and are in reality separated by vast distances from one another. But the great majority have not only an apparent, but also a real closeness; and in a number of cases this is proved by the fact that observation shows the stars in question to be physically connected, and to revolve around a common centre of gravity. Double stars which are thus physically connected are known as 'binaries.' The discovery of the existence of this real connection between some double stars is due, like so many of the most interesting astronomical discoveries, to Sir William Herschel. At present the number of stars known to be binary is somewhat under one thousand; but in the case of most of these, the revolution round a common centre which proves their physical connection is extremely slow, and consequently the majority of binary stars have as yet been followed only through a small portion of their orbits, and the change of position sufficient to enable a satisfactory orbit to be computed has occurred in only a small proportion of the total number. The first binary star to have its orbit computed was Xi UrsÆ Majoris, whose revolution of about sixty years has been twice completed since, in 1780, Sir William Herschel discovered it to be double.

The star which has the shortest period at present known is the fourth magnitude Delta Equulei, which has a fifth magnitude companion. The pair complete their revolution, according to Hussey, in 5·7 years. Kappa Pegasi comes next in speed of revolution, with a period of eleven and a half years, while the star 85 of the same constellation takes rather more than twice as long to complete its orbit. From such swiftly circling pairs as these, the periods range up to hundreds of years. Thus, for example, the well-known double star Castor, probably the most beautiful double in the northern heavens, and certainly the best object of its class for a small telescope, is held to have a period of 347 years, which, though long enough, is a considerable reduction upon the 1,000 once attributed to it.

But the number of binary stars known is not confined to those which have been discovered and measured by means of the telescope and micrometer. One of the most wonderful results of modern astronomical research has been the discovery of the fact that many stars have revolving round them invisible companions, which are either dark bodies, or else are so close to their primaries as for ever to defy the separating powers of our telescopes. The discovery of these dark, or at least invisible, companions is one of the most remarkable triumphs of the spectroscope. It was in 1888 that Vogel first applied the spectroscopic method to the well-known variable star, Beta Persei—known as Algol, 'the Demon,' from its 'slowly-winking eye.' The variation in the light of Algol is very large, from second to fourth magnitude; Vogel therefore reasoned that if this variation were caused by a dark companion partially eclipsing the bright star, the companion must be sufficiently large to cause motion in Algol—that is, to cause both stars to revolve round a common centre of gravity. Should this be the case, then at one point of its orbit Algol must be approaching, and at the opposite point receding from the earth; and therefore the shift of the lines of its spectrum towards the violet in the one instance and towards the red in the other would settle the question of whether it had or had not an invisible companion. The spectroscopic evidence proved quite conclusive. It was found that before its eclipses, Algol was receding from the sun at the rate of 26? miles per second, while after eclipse there was a similar motion of approach; and therefore the hypothesis of an invisible companion was proved to be fact. Vogel carried his researches further, his inquiry into the questions of the size and distance apart of the two bodies leading him to the conclusion that the bright star is rather more, and its companion rather less than 1,000,000 miles in diameter; while the distance which divides them is somewhat more than 3,000,000 miles. Though larger, both bodies prove to be less massive than our sun, Algol being estimated at four-ninths and its companion at two-ninths of the solar mass.

The class of double star disclosed in this manner is known as the 'spectroscopic binary,' and has various other types differing from the Algol type. Thus the type of which Xi UrsÆ Majoris was the first detected instance has two component bodies not differing greatly in brightness from one another. In such a case the fact of the star being binary is revealed through the consideration that in any binary system the two components must necessarily always be moving in opposite directions. Hence the shift of the lines of their spectrum will be in opposite directions also, and when one of the stars (A) is moving towards us, and the other (B) away from us, all the lines of the spectrum which are common to the two will appear double, those of A being displaced towards the violet and those of B towards the red. After a quarter of a revolution, when the stars are momentarily in a straight line with us, the lines will all appear single; but after half a revolution they will again be displaced, those of A this time towards the red and those of B towards the violet.

There has thus been opened up an entirely new field of research, and the idea, long cherished, that the stars might prove to have dark, or, at all events, invisible, companions attendant on them, somewhat as our own sun has its planets, has been proved to be perfectly sound. So far, in the case of dark companions, only bodies of such vast size have been detected as to render any comparison with the planets of our system difficult; but the principle is established, and the probability of great numbers of the stars having real planetary systems attendant on them is so great as to become practically a certainty. 'We naturally infer,' says Professor Newcomb, 'that ... innumerable stars may have satellites, planets, or companion stars so close or so faint as to elude our powers of observation.'

From the consideration of spectroscopic binaries we naturally turn to that of variable stars, the two classes being, to some extent at least, coincident, as is evidenced by the case of Algol. While the discovery of spectroscopic binaries is one of the latest results of research, that of variability among stars dates from comparatively far back in the history of astronomy. As early as the year 1596 David Fabricius noted the star now known as Omicron Ceti, or Mira, 'the Wonderful,' as being of the third magnitude, while in the following year he found that it had vanished. A succession of appearances and disappearances was witnessed in the middle of the next century by Holwarda, and from that time the star has been kept under careful observation, and its variations have been determined with some exactness, though there are anomalies as yet unexplained. 'Once in eleven months,' writes Miss Clerke, 'the star mounts up in about 125 days from below the ninth to near the third, or even to the second magnitude; then, after a pause of two or three weeks, drops again to its former low level in once and a half times, on an average, the duration of its rise.' This most extraordinary fluctuation means that at a bright maximum Mira emits 1,500 times as much light as at a low minimum. The star thus subject to such remarkable outbursts is, like most variables, of a reddish colour, and at maximum its spectrum shows the presence of glowing hydrogen. Its average period is about 331 days; but this period is subject to various irregularities, and the maximum has sometimes been as much as two months away from the predicted time. Mira Ceti may be taken as the type of the numerous class of stars known as 'long-period variables.'

Not less interesting are those stars whose variations cover only short periods, extending from less than thirty days down to a few hours. Of these, perhaps the most easily observed, as it is also one of the most remarkable, is Beta LyrÆ. This star is one of the two bright stars of nearly equal magnitude which form an obtuse-angled triangle with the brilliant first-magnitude star Vega. The other star of the pair is Gamma LyrÆ, and between them lies the famous Ring Nebula, to be referred to later. Ordinarily Beta LyrÆ is of magnitude 3·4, but from this it passes, in a period of rather less than thirteen days, through two minima, in one of which it descends to magnitude 3·9 and in the other to 4·5. This fluctuation seems trifling. It really means, however, that at maximum the star is two and three-quarter times brighter than when it sinks to magnitude 4·5; and the variation can be easily recognised by the naked eye, owing to the fact of the nearness of so convenient a comparison star as Gamma LyrÆ. Beta LyrÆ is a member of the class of spectroscopic binaries, and belongs to that type of the class in which the mutually eclipsing bodies are both bright. In such cases the variation in brilliancy is caused by the fact that when the two bodies are, so to speak, side by side, light is received from both of them, and a maximum is observed; while, when they are end on, both in line with ourselves, one cuts off more or less of the other's light from us, thus causing a minimum.

A third class, distinct from either of the preceding, is that of the Algol Variables, so-called from the bright star Beta Persei, which has already been mentioned as a spectroscopic binary. Than this star there is no more notable variable in the heavens, and its situation fortunately renders it peculiarly easy of observation to northern students. Algol shines for about fifty-nine hours as a star of small second magnitude, then suddenly begins to lose light, and in four and a half hours has fallen to magnitude three and a half, losing in so short a space two-thirds of its normal brilliancy. It remains in this degraded condition for only fifteen minutes, and then begins to recover, reaching its normal lustre in about five hours more. These remarkable changes, due, as before mentioned, to the presence of an invisible eclipsing companion, are gone through with the utmost regularity, so much so that, as Gore says, the minima of Algol 'can be predicted with as much certainty as an eclipse of the sun.' The features of the type-star are more or less closely reproduced in the other Algol Variables—a comparatively long period of steady light emission, followed by a rapid fall to one or more minima, and a rapid recovery of light. The class as yet is a small one, but new members are gradually being added to it, the majority of them white, like the type-star.

The study of variable stars is one which should seem to be specially reserved for the amateur observer. In general, it requires but little instrumental equipment. Many variables can be seen at maximum, some even at minimum, with the unaided eye; in other cases a good opera or field glass is all that is required, and a 2½ or 3-inch telescope will enable the observer to command quite an extensive field of work. Here, again, the beginner may be referred to the Memoirs of the British Astronomical Association for help and guidance, and may be advised to connect himself with the Variable Star Section.

With the exception of such variations in the lustre of certain stars as have been described, the aspect of the heavens is, in general, fixed and unchanging. There are, as we shall see, real changes of the vastest importance continually going on; but the distances separating us from the fixed stars are so enormous that these changes shrink into nothingness, and the astronomers of forty centuries before our era would find comparatively little change today in the aspect of the constellations with which they were familiar. But occasionally a very remarkable change does take place, in the apparition of a new or temporary star. The accounts of the appearance of such objects are not very numerous, but are of great interest. We pass over those recorded, in more or less casual fashion, by the ancients, for the reason that the descriptions given are in general more picturesque than illuminative. It does not add much to one's knowledge, though it may excite wonder, to find the Chinese annals recording the appearance, in A.D. 173, of a new star 'resembling a large bamboo mat!'

The first Nova, of which we have a really scientific record, was the star which suddenly blazed out, in November, 1572, in the familiar W of Cassiopeia. It was carefully observed by the great astronomer, Tycho BrahÉ, and, according to him, was brighter than Sirius, Alpha LyrÆ, or Jupiter. Tycho followed it till March, 1574, by which time it had sunk to the limit of unaided vision, and further observation became impossible. There is at present a star of the eleventh magnitude close to the place fixed for the Nova from Tycho's observations. In 1604 and 1670, new stars were observed, the first by Kepler and his assistants, the second by the monk Anthelme; but from 1670 there was a long break in the list of discoveries, which was ended by Hind's observation of a new star in Ophiuchus (April, 1848). This was never a very conspicuous object, rising only to somewhat less than fourth magnitude, and soon fading to tenth or eleventh. We can only mention the 'Blaze Star' of Corona Borealis, discovered by Birmingham in 1866, the Nova discovered in 1876 by Schmidt of Athens, near Rho Cygni—an object which seems to have faded out into a planetary nebula, a fate apparently characteristic of this class of star—and the star which appeared in 1885, close to the nucleus of the Great Nebula in Andromeda.

In 1892, Dr. Anderson of Edinburgh discovered in the constellation Auriga a star which he estimated as of fifth magnitude. The discovery was made on January 31, and the new star was found to have been photographed at Harvard on plates taken from December 16, 1891, to January 31, 1892. Apparently this Nova differed from other temporary stars in the fact that it attained its full brightness only gradually. By February 3 it rose to magnitude 3·5, then faded by April 1 to fifteenth, but in August brightened up again to about ninth magnitude. It is now visible as a small star. The great development of spectroscopic resources brought this object, otherwise not a very conspicuous one, under the closest scrutiny. Its spectrum showed many bright lines, which were accompanied by dark ones on the side next the blue. The idea was thus suggested that the outburst of brilliancy was due to a collision between two bodies, one of which, that causing the dark lines, was approaching the earth, while the other was receding from it. Lockyer considered the conflagration to be due to a collision between two swarms of meteorites, Huggins that it was caused by the near approach to one another of two gaseous bodies, while others suggested that the rush of a star or of a swarm of meteorites through a nebula would explain the facts observed. Subsequent observations of the spectrum of Nova AurigÆ have revealed the fact that it has obeyed the destiny which seems to wait on temporary stars, having become a planetary nebula.

Dr. Anderson followed up his first achievement by the discovery of a brilliant Nova in the constellation Perseus. The discovery was made on the night of February 21-22, 1901, the star being then of magnitude 2·7. Within two days it became about the third brightest star in the sky, being a little more brilliant than Capella; but before the middle of April it had sunk to fifth magnitude. The rapidity of its rise must have been phenomenal! A plate exposed at Harvard on February 19, and showing stars to the eleventh magnitude, bore no trace of the Nova. 'It must therefore,' says Newcomb, 'have risen from some magnitude below the eleventh to the first within about three days. This difference corresponds to an increase of the light ten thousandfold!' Such a statement leaves the mind simply appalled before the spectacle of a cataclysm so infinitely transcending the very wildest dreams of fancy. Subsequent observations have shown the usual tendency towards development into a nebula, and in August, 1901, photographs were actually obtained of a nebulosity round the star, showing remarkable condensations. These photographs, taken at Yerkes Observatory, when compared with others taken at Mount Hamilton in November, revealed the startling fact that the condensations of the nebula were apparently in extraordinarily rapid motion. Now the Nova shows no appreciable parallax, or in other words is so distant that its distance cannot be measured; on what scale, therefore, must these motions have been to be recorded plainly across a gulf measurable perhaps in hundreds of light years!

Nova Geminorum, discovered by Professor Turner, at Oxford, in March, 1903, had not the striking features which lent so much interest to Nova Persei. It showed a crimson colour, and its spectrum indicated the presence in its blaze of hydrogen and helium; but it faded so rapidly as to show that the disturbance affected a comparatively small body, and it has exhibited the familiar new star change into a nebula.

One point with regard to the NovÆ in Auriga and Perseus deserves notice. These discoveries, so remarkable in themselves, and so fruitful in the extension of our knowledge, were made by an amateur observer with no greater equipment than a small pocket telescope and a Klein's Star-Atlas. The thorough knowledge of the face of the heavens which enabled Dr. Anderson to pick out the faint glimmer of Nova AurigÆ and to be certain that the star was a new one is not in the least unattainable by anyone who cares to give time and patience to its acquisition; and even should the study never be rewarded by a capture so dramatic as that of Nova Persei, the familiarity gained in its course with the beauty and wonder of the star-sphere will in itself be an ample reward.