Read CHAPTER VI - SUNS IN FLAMES. of Myths and Marvels of Astronomy , free online book, by Richard A. Proctor, on ReadCentral.com.

In November 1876 news arrived of a catastrophe the effects of which must in all probability have been disastrous, not to a district, or a country, or a continent, or even a world, but to a whole system of worlds. The catastrophe happened many years ago probably at least a hundred yet the messenger who brought the news has not been idle on his way, but has sped along at a rate which would suffice to circle this earth eight times in the course of a second. That messenger has had, however, to traverse millions of millions of miles, and only reached our earth November 1876. The news he brought was that a sun like our own was in conflagration; and on a closer study of his message something was learned as to the nature of the conflagration, and a few facts tending to throw light on the question (somewhat interesting to ourselves) whether our own sun is likely to undergo a similar mishap at any time. What would happen if he did, we know already. The sun which has just met with this disaster that is, which so suffered a few generations ago blazed out for a time with several hundred times its former lustre. If our sun were to increase as greatly in light and heat, the creatures on the side of our earth turned towards him at the time would be destroyed in an instant. Those on the dark or night hemisphere would not have to wait for their turn till the earth, by rotating, carried them into view of the destroying sun. In much briefer space the effect of his new fires would be felt all over the earth’s surface. The heavens would be dissolved and the elements would melt with fervent heat. In fact no description of such a catastrophe, as affecting the night half of the earth, could possibly be more effective and poetical than St. Peter’s account of the day of the Lord, coming ’as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein being burned up;’ though I imagine the apostle would have been scarce prepared to admit that the earth was in danger from a solar conflagration. Indeed, according to another account, the sun was to be turned into darkness and the moon into blood, before that great and notable day of the Lord came a description corresponding well with solar and lunar eclipses, the most noteworthy ‘signs in the heavens,’ but agreeing very ill with the outburst of a great solar conflagration.

Before proceeding to inquire into the singular and significant circumstances of the recent outburst, it may be found interesting to examine briefly the records which astronomy has preserved of similar catastrophes in former years. These may be compared to the records of accidents on the various railway lines in a country or continent. Those other suns which we can stars are engines working the mighty mechanism of planetary systems, as our sun maintains the energies of our own system; and it is a matter of some interest to us to inquire in how many cases, among the many suns within the range of vision, destructive explosions occur. We may take the opportunity, later, to inquire into the number of cases in which the machinery of solar systems appears to have broken down.

The first case of a solar conflagration on record is that of the new star observed by Hipparchus some 2000 years ago. In his time, and indeed until quite recently, an object of this kind was called a new star, or a temporary star. But we now know that when a star makes its appearance where none had before been visible, what has really happened has been that a star too remote to be seen has become visible through some rapid increase of splendour. When the new splendour dies out again, it is not that a star has ceased to exist; but simply that a faint star which had increased greatly in lustre has resumed its original condition. Hipparchus’s star must have been a remarkable object, for it was visible in full daylight, whence we may infer that it was many times brighter than the blazing Dog-star. It is interesting in the history of science, as having led Hipparchus to draw up a catalogue of stars, the first on record. Some moderns, being sceptical, rejected this story as a fiction; but Biot examining Chinese Chronicles relating to the times of Hipparchus, finds that in 134 B.C. (about nine years before the date of Hipparchus’s catalogue) a new star was recorded as having appeared in the constellation Scorpio.

The next new star (that is, stellar conflagration) on record is still more interesting, as there appears some reason for believing that before long we may see another outburst of the same star. In the years 945, 1264, and 1572, brilliant stars appeared in the region of the heavens between Cepheus and Cassiopeia. Sir J. Herschel remarks, that, ’from the imperfect account we have of the places of the two earlier, as compared with that of the last, which was well determined, as well as from the tolerably near coincidence of the intervals of their appearance, we may suspect them, with Goodricke, to be one and the same star, with a period of 312 or perhaps of 156 years.’ The latter period may very reasonably be rejected, as one can perceive no reason why the intermediate returns of the star to visibility should have been overlooked, the star having appeared in a region which never sets. It is to be noted that, the period from 945 to 1264 being 319 years, and that from 1264 to 1572 only 308 years, the period of this star (if Goodricke is correct in supposing the three outbursts to have occurred in the same star) would seem to be diminishing. At any time, then, this star might now blaze out in the region between Cassiopeia and Cepheus, for more than 304 years have already passed since its last outburst.

As the appearance of a new star led Hipparchus to undertake the formation of his famous catalogue, so did the appearance of the star in Cassiopeia, in 1572, lead the Danish astronomer Tycho Brahe to construct a new and enlarged catalogue. (This, be it remembered, was before the invention of the telescope.) Returning one evening (November 11, 1572, old style) from his laboratory to his dwelling-house, he found, says Sir J. Herschel, ’a group of country people gazing at a star, which he was sure did not exist an hour before. This was the star in question.’

The description of the star and its various changes is more interesting at the present time, when the true nature of these phenomena is understood, than it was even in the time when the star was blazing in the firmament. It will be gathered from that description and from what I shall have to say farther on about the results of recent observations on less splendid new stars, that, if this star should reappear in the next few years, our observers will probably be able to obtain very important information from it. The message from it will be much fuller and more distinct than any we have yet received from such stars, though we have learned quite enough to remain in no sort of doubt as to their general nature.

The star remained visible, we learn, about sixteen months, during which time it kept its place in the heavens without the least variation. ’It had all the radiance of the fixed stars, and twinkled like them; and was in all respects like Sirius, except that it surpassed Sirius in brightness and magnitude.’ It appeared larger than Jupiter, which was at that time at his brightest, and was scarcely inferior to Venus. It did not acquire this lustre gradually, but shone forth at once of its full size and brightness, ‘as if,’ said the chroniclers of the time, ’it had been of instantaneous creation.’ For three weeks it shone with full splendour, during which time it could be seen at noonday ’by those who had good eyes, and knew where to look for it.’ But before it had been seen a month, it became visibly smaller, and from the middle of December 1572 till March 1574, when it entirely disappeared, it continually diminished in magnitude. ’As it decreased in size, it varied in colour: at first its light was white and extremely bright; it then became yellowish; afterwards of a ruddy colour like Mars; and finished with a pale livid white resembling the colour of Saturn.’ All the details of this account should be very carefully noted. It will presently be seen that they are highly characteristic.

Those who care to look occasionally at the heavens to know whether this star has returned to view may be interested to learn whereabouts it should be looked for. The place may be described as close to the back of the star-gemmed chair in which Cassiopeia is supposed to sit a little to the left of the seat of the chair, supposing the chair to be looked at in its normal position. But as Cassiopeia’s chair is always inverted when the constellation is most conveniently placed for observation, and indeed as nine-tenths of those who know the constellation suppose the chair’s legs to be the back, and vice versa, it may be useful to mention that the star was placed somewhat thus with respect to the straggling W formed by the five chief stars of Cassiopeia. There is a star not very far from the place here indicated, but rather nearer to the middle angle of the W. This, however, is not a bright star; and cannot possibly be mistaken for the expected visitant. (The place of Tycho’s star is indicated in my School Star-Atlas and also in my larger Library Atlas. The same remark applies to both the new stars in the Serpent-Bearer, presently to be described.)

In August 1596 the astronomer Fabricius observed a new star in the neck of the Whale, which also after a time disappeared. It was not noticed again till the year 1637, when an observer rejoicing in the name of Phocyllides Holwarda observed it, and, keeping a watch, after it had vanished, upon the place where it had appeared, saw it again come into view nine months after its disappearance. Since then it has been known as a variable star with a period of about 331 days 8 hours. When brightest this star is of the second magnitude. It indicates a somewhat singular remissness on the part of the astronomers of former days, that a star shining so conspicuously for a fortnight, once in each period of 331-1/3 days, should for so many years have remained undetected. It may, perhaps, be thought that, noting this, I should withdraw the objection raised above against Sir J. Herschel’s idea that the star in Cassiopeia may return to view once in 156 years, instead of once in 312 years. But there is a great difference between a star which at its brightest shines only as a second-magnitude star, so that it has twenty or thirty companions of equal or greater lustre above the horizon along with it, and a star which surpasses three-fold the splendid Sirius. We have seen that even in Tycho Brahe’s day, when probably the stars were not nearly so well known by the community at large, the new star in Cassiopeia had not shone an hour before the country people were gazing at it with wonder. Besides, Cassiopeia and the Whale are constellations very different in position. The familiar stars of Cassiopeia are visible on every clear night, for they never set. The stars of the Whale, at least of the part to which the wonderful variable star belongs, are below the horizon during rather more than half the twenty-four hours; and a new star there would only be noticed, probably (unless of exceeding splendour), if it chanced to appear during that part of the year when the Whale is high above the horizon between eventide and midnight, or in the autumn and early winter.

It is a noteworthy circumstance about the variable star in the Whale, deservedly called Mira, or The Wonderful, that it does not always return to the same degree of brightness. Sometimes it has been a very bright second-magnitude star when at its brightest, at others it has barely exceeded the third magnitude. Hevelius relates that during the four years between October 1672 and December 1676, Mira did not show herself at all! As this star fades out, it changes in colour from white to red.

Towards the end of September 1604, a new star made its appearance in the constellation Ophiuchus, or the Serpent-Bearer. Its place was near the heel of the right foot of ‘Ophiuchus huge.’ Kepler tells us that it had no hair or tail, and was certainly not a comet. Moreover, like the other fixed stars, it kept its place unchanged, showing unmistakably that it belonged to the star-depths, not to nearer regions. ’It was exactly like one of the stars, except that in the vividness of its lustre, and the quickness of its sparkling, it exceeded anything that he had ever seen before. It was every moment changing into some of the colours of the rainbow, as yellow, orange, purple, and red; though it was generally white when it was at some distance from the vapours of the horizon.’ In fact, these changes of colour must not be regarded as indicating aught but the star’s superior brightness. Every very bright star, when close to the horizon, shows these colours, and so much the more distinctly as the star is the brighter. Sirius, which surpasses the brightest stars of the northern hemisphere full four times in lustre, shows these changes of colour so conspicuously that they were regarded as specially characteristic of this star, insomuch that Homer speaks of Sirius (not by name, but as the ‘star of autumn’) shining most beautifully ’when laved of ocean’s wave’ that is, when close to the horizon. And our own poet, Tennyson, following the older poet, sings how

the fiery Sirius alters hue,
And bickers into red and emerald.

The new star was brighter than Sirius, and was about five degrees lower down, when at its highest above the horizon, than Sirius when he culminates. Five degrees being equal to nearly ten times the apparent diameter of the moon, it will be seen how much more favourable the conditions were in the case of Kepler’s star for those coloured scintillations which characterised that orb. Sirius never rises very high above the horizon. In fact, at his highest (near midnight in winter, and, of course, near midday in summer) he is about as high above the horizon as the sun at midday in the first week in February. Kepler’s star’s greatest height above the horizon was little more than three-fourths of this, or equal to about the sun’s elevation at midday on January 13 or 14 in any year.

Like Tycho Brahe’s star, Kepler’s was brighter even than Jupiter, and only fell short of Venus in splendour. It preserved its lustre for about three weeks, after which time it gradually grew fainter and fainter until some time between October 1605 and February 1606, when it disappeared. The exact day is unknown, as during that interval the constellation of the Serpent-Bearer is above the horizon in the day-time only. But in February 1606, when it again became possible to look for the new star in the night-time, it had vanished. It probably continued to glow with sufficient lustre to have remained visible, but for the veil of light under which the sun concealed it, for about sixteen months altogether. In fact, it seems very closely to have resembled Tycho’s star, not only in appearance and in the degree of its greatest brightness, but in the duration of its visibility.

In the year 1670 a new star appeared in the constellation Cygnus, attaining the third magnitude. It remained visible, but not with this lustre, for nearly two years. After it had faded almost out of view, it flickered up again for awhile, but soon after it died out, so as to be entirely invisible. Whether a powerful telescope would still have shown it is uncertain, but it seems extremely probable. It may be, indeed, that this new star in the Swan is the same which has made its appearance within the last few weeks; but on this point the evidence is uncertain.

On April 20, 1848, Mr. Hind (Superintendent of the Nautical Almanac, and discoverer of ten new members of the solar system) noticed a new star of the fifth magnitude in the Serpent-Bearer, but in quite another part of that large constellation than had been occupied by Kepler’s star. A few weeks later, it rose to the fourth magnitude. But afterwards its light diminished until it became invisible to ordinary eyesight. It did not vanish utterly, however. It is still visible with telescopic power, shining as a star of the eleventh magnitude, that is five magnitudes below the faintest star discernible with the unaided eye.

This is the first new star which has been kept in view since its apparent creation. But we are now approaching the time when it was found that as so-called new stars continue in existence long after they have disappeared from view, so also they are not in reality new, but were in existence long before they became visible to the naked eye.

On May 12, 1866, shortly before midnight, Mr. Birmingham, of Tuam, noticed a star of the second magnitude in the Northern Crown, where hitherto no star visible to the naked eye had been known. Dr. Schmidt, of Athens, who had been observing that region of the heavens the same night, was certain that up to 11 P.M., Athens local time, there was no star above the fourth magnitude in the place occupied by the new star. So that, if this negative evidence can be implicitly relied on, the new star must have sprung at least from the fourth, and probably from a much lower magnitude, to the second, in less than three hours eleven o’clock at Athens corresponding to about nine o’clock by Irish railway time. A Mr. Barker, of London, Canada, put forward a claim to having seen the new star as early as May 4 a claim not in the least worth investigating, so far as the credit of first seeing the new star is concerned, but exceedingly important in its bearing on the nature of the outburst affecting the star in Corona. It is unpleasant to have to throw discredit on any definite assertion of facts; unfortunately, however, Mr. Barker, when his claim was challenged, laid before Mr. Stone, of the Greenwich Observatory, such very definite records of observations made on May 4, 8, 9, and 10, that we have no choice but either to admit these observations, or to infer that he experienced the delusive effects of a very singular trick of memory. He mentions in his letter to Mr. Stone that he had sent full particulars of his observations on those early dates to Professor Watson, of Ann Arbor University, on May 17; but (again unfortunately) instead of leaving that letter to tell its own story in Professor Watson’s hands, he asked Professor Watson to return it to him: so that when Mr. Stone very naturally asked Professor Watson to furnish a copy of this important letter, Professor Watson had to reply, ’About a month ago, Mr. Barker applied to me for this letter, and I returned it to him, as requested, without preserving a copy. I can, however,’ he proceeded, ’state positively that he did not mention any actual observation earlier than May 14. He said he thought he had noticed a strange star in the Crown about two weeks before the date of his first observation May 14 but not particularly, and that he did not recognise it until the 14th. He did not give any date, and did not even seem positive as to identity.... When I returned the letter of May 17, I made an endorsement across the first page, in regard to its genuineness, and attached my signature. I regret that I did not preserve a copy of the letter in question; but if the original is produced, it will appear that my recollection of its contents is correct.’ I think no one can blame Mr. Stone, if, on the receipt of this letter, he stated that he had not the ‘slightest hesitation’ in regarding Mr. Barker’s earlier observations as ’not entitled to the slightest credit.’

It may be fairly taken for granted that the new star leapt very quickly, if not quite suddenly, to its full splendour. Birmingham, as we have seen, was the first to notice it, on May 12. On the evening of May 13, Schmidt of Athens discovered it independently, and a few hours later it was noticed by a French engineer named Courbebaisse. Afterwards, Baxendell of Manchester, and others independently saw the star. Schmidt, examining Argelander’s charts of 324,000 stars (charts which I have had the pleasure of mapping in a single sheet), found that the star was not a new one, but had been set down by Argelander as between the ninth and tenth magnitudes. Referring to Argelander’s list, we find that the star had been twice observed viz., on May 18, 1855, and on March 31, 1856.

Birmingham wrote at once to Mr. Huggins, who, in conjunction with the late Dr. Miller, had been for some time engaged in observing stars and other celestial objects with the spectroscope. These two observers at once directed their telescope armed with spectroscopic adjuncts the telespectroscope is the pleasing name of the compound instrument to the new-comer. The result was rather startling. It may be well, however, before describing it, to indicate in a few words the meaning of various kinds of spectroscopic evidence.

The light of the sun, sifted out by the spectroscope, shows all the colours but not all the tints of the rainbow. It is spread out into a large rainbow-tinted streak, but at various places (a few thousand) along the streak there are missing tints; so that in fact the streak is crossed by a multitude of dark lines. We know that these lines are due to the absorptive action of vapours existing in the atmosphere of the sun, and from the position of the lines we can tell what the vapours are. Thus, hydrogen by its absorptive action produces four of the bright lines. The vapour of iron is there, the vapour of sodium, magnesium, and so on. Again, we know that these same vapours, which, by their absorptive action, cut off rays of certain tints, emit light of just those tints. In fact, if the glowing mass of the sun could be suddenly extinguished, leaving his atmosphere in its present intensely heated condition, the light of the faint sun which would thus be left us would give (under spectroscopic scrutiny) those very rays which now seem wanting. There would be a spectrum of multitudinous bright lines, instead of a rainbow-tinted spectrum crossed by multitudinous dark lines. It is, indeed, only by contrast that the dark lines appear dark, just as it is only by contrast that the solar spots seem dark. Not only the penumbra but the umbra of a sun-spot, not only the umbra but the nucleus, not only the nucleus but the deeper black which seems to lie at the core of the nucleus, shine really with a lustre far exceeding that of the electric light, though by contrast with the rest of the sun’s surface the penumbra looks dark, the umbra darker still, the nucleus deep black, and the core of the nucleus jet black. So the dark lines across the solar spectrum mark where certain rays are relatively faint, though in reality intensely lustrous. Conceive another change than that just imagined. Conceive the sun’s globe to remain as at present, but the atmosphere to be excited to many times its present degree of light and splendour: then would all these dark lines become bright, and the rainbow-tinted background would be dull or even quite dark by contrast. This is not a mere fancy. At times, local disturbances take place in the sun which produce just such a change in certain constituents of the sun’s atmosphere, causing the hydrogen, for example, to glow with so intense a heat that, instead of its lines appearing dark, they stand out as bright lines. Occasionally, too, the magnesium in the solar atmosphere (over certain limited regions only, be it remembered) has been known to behave in this manner. It was so during the intensely hot summer of 1872, insomuch that the Italian observer Tacchini, who noticed the phenomenon, attributed to such local overheating of the sun’s magnesium vapour the remarkable heat from which we then for a time suffered.

Now, the stars are suns, and the spectrum of a star is simply a miniature of the solar spectrum. Of course, there are characteristic differences. One star has more hydrogen, at least more hydrogen at work absorbing its rays, and thus has the hydrogen lines more strongly marked than they are in the solar spectrum. Another star shows the lines of various metals more conspicuously, indicating that the glowing vapours of such elements, iron, copper, mercury, tin, and so forth, either hang more densely in the star’s atmosphere than in our sun’s, or, being cooler, absorb their special tints more effectively. But speaking generally, a stellar spectrum is like the solar spectrum. There is the rainbow-tinted streak, which implies that the source of light is glowing solid, liquid, or highly compressed vaporous matter, and athwart the streak there are the multitudinous dark lines which imply that around the glowing heart of the star there are envelopes of relatively cool vapours.

We can understand, then, the meaning of the evidence obtained from the new star in the Northern Crown.

In the first place, the new star showed the rainbow-tinted streak crossed by dark lines, which indicated its sun-like nature. But, standing out on that rainbow-tinted streak as on a dark background, were four exceedingly bright lines lines so bright, though fine, that clearly most of the star’s light came from the glowing vapours to which these lines belonged. Three of the lines belonged to hydrogen, the fourth was not identified with any known line.

Let us distinguish between what can certainly be concluded from this remarkable observation, and what can only be inferred with a greater or less degree of probability.

It is absolutely certain that when Messrs. Huggins and Miller made their observation (by which time the new star had faded from the second to the third magnitude), enormous masses of hydrogen around the star were glowing with a heat far more intense than that of the star itself within the hydrogen envelope. It is certain that the increase in the star’s light, rendering the star visible which before had been far beyond the range of ordinary eyesight, was due to the abnormal heat of the hydrogen surrounding that remote sun.

But it is not so clear whether the intense glow of the hydrogen was caused by combustion or by intense heat without combustion. The difference between the two causes of increased light is important; because on the opinion we form on this point must depend our opinion as to the probability that our sun may one day experience a similar catastrophe, and also our opinion as to the state of the sun in the Northern Crown after the outburst. To illustrate the distinction in question, let us take two familiar cases of the emission of light. A burning coal glows with red light, and so does a piece of iron placed in a coal fire. But the coal and the iron are undergoing very different processes. The coal is burning, and will presently be consumed; the iron is not burning (except in the sense that it is burning hot, which means only that it will make any combustible substance burn which is brought into contact with it), and it will not be consumed though the coal fire be maintained around it for days and weeks and months. So with the hydrogen flames which play at all times over the surface of our own sun. They are not burning like the hydrogen flames which are used for the oxy-hydrogen lantern. Were the solar hydrogen so burning, the sun would quickly be extinguished. They are simply aglow with intensity of heat, as a mass of red-hot iron is aglow; and, so long as the sun’s energies are maintained, the hydrogen around him will glow in this way without being consumed. As the new fires of the star in the Crown died out rapidly, it is possible that in their case there was actual combustion. On the other hand, it is also possible, and perhaps on the whole more probable, that the hydrogen surrounding the star was simply set glowing with increased lustre owing to some cause not as yet ascertained.

Let us see how these two theories have been actually worded by the students of science themselves who have maintained them.

‘The sudden blazing forth of this star,’ says Mr. Huggins, ’and then the rapid fading away of its light, suggest the rather bold speculation that in consequence of some great internal convulsion, a large volume of hydrogen and other gases was evolved from it, the hydrogen, by its combination with some other element,’ in other words, by burning, ’giving out the light represented by the bright lines, and at the same time heating to the point of vivid incandescence the solid matter of the star’s surface.’ ‘As the liberated hydrogen gas became exhausted’ (I now quote not Huggins’s own words, but words describing his theory in a book which he has edited) ’the flame gradually abated, and, with the consequent cooling, the star’s surface became less vivid, and the star returned to its original condition.’

On the other hand, the German physicists, Meyer and Klein, consider the sudden development of hydrogen, in quantities sufficient to explain such an outburst, exceedingly unlikely. They have therefore adopted the opinion, that the sudden blazing out of the star was occasioned by the violent precipitation of some mighty mass, perhaps a planet, upon the globe of that remote sun, ’by which the momentum of the falling mass would be changed into molecular motion, or in other words into heat and light.’ It might even be supposed, they urge, that the star in the Crown, by its swift motion, may have come in contact with one of the star clouds which exist in large numbers in the realms of space. ’Such a collision would necessarily set the star in a blaze and occasion the most vehement ignition of its hydrogen.’

Fortunately, our sun is safe for many millions of years to come from contact from any one of its planets. The reader must not, however, run away with the idea that the danger consists only in the gradual contraction of planetary orbits sometimes spoken of. That contraction, if it is taking place at all, of which we have not a particle of evidence, would not draw Mercury to the sun’s surface for at least ten million millions of years. The real danger would be in the effects which the perturbing action of the larger planets might produce on the orbit of Mercury. That orbit is even now very eccentric, and must at times become still more so. It might, but for the actual adjustment of the planetary system, become so eccentric that Mercury could not keep clear of the sun; and a blow from even small Mercury (only weighing, in fact, 390 millions of millions of millions of tons), with a velocity of some 300 miles per second, would warm our sun considerably. But there is no risk of this happening in Mercury’s case though the unseen and much more shifty Vulcan (in which planet I beg to express here my utter disbelief) might, perchance, work mischief if he really existed.

As for star clouds lying in the sun’s course, we may feel equally confident. The telescope assures us that there are none immediately on the track, and we know, also, that, swiftly though the sun is carrying us onwards through space, many millions of years must pass before he is among the star families towards which he is rushing.

Of the danger from combustion, or from other causes of ignition than those considered by Meyer and Klein, it still remains to speak. But first, let us consider what new evidence has been thrown upon the subject by the observations made on the star which flamed out last November.

The new star was first seen by Professor Schmidt, who has had the good fortune of announcing to astronomers more than one remarkable phenomenon. It was he who discovered in November 1866 that a lunar crater had disappeared, an announcement quite in accordance with the facts of the case. We have seen that he was one of the independent discoverers of the outburst in the Northern Crown. On November 24, at the early hour of 5.41 in the evening (showing that Schmidt takes time by the forelock at his observatory), he noticed a star of the third magnitude in the constellation of the Swan, not far from the tail of that southward-flying celestial bird. He is quite sure that on November 20, the last preceding clear evening, the star was not there. At midnight its light was very yellow, and it was somewhat brighter than the neighbouring star Eta Pegasi, on the Flying Horse’s southernmost knee (if anatomists will excuse my following the ordinary usage which calls the wrist of the horse’s fore-arm the knee). He sent news of the discovery forthwith to Leverrier, the chief of the Paris observatory; and the observers there set to work to analyse the light of the stranger. Unfortunately the star’s suddenly acquired brilliancy rapidly faded. M. Paul Henry estimated the star’s brightness on December 2 as equal only to that of a fifth-magnitude star. Moreover, the colour, which had been very yellow on November 24, was by this time ’greenish, almost blue.’ On December 2, M. Cornu, observing during a short time when the star was visible through a break between clouds, found that the star’s spectrum consisted almost entirely of bright lines. On December 5, he was able to determine the position of these lines, though still much interrupted by clouds. He found three bright lines of hydrogen, the strong (really double) line of sodium, the (really triple) line of magnesium, and two other lines. One of these last seemed to agree exactly in position with a bright line belonging to the corona seen around the sun during total eclipse.

The star has since faded gradually in lustre until, at present, it is quite invisible to the naked eye.

We cannot doubt that the catastrophe which befell this star is of the same general nature as is that which befell the star in the Northern Crown. It is extremely significant that all the elements which manifested signs of intense heat in the case of the star in the Swan, are characteristic of our sun’s outer appendages. We know that the coloured flames seen around the sun during total solar eclipse consist of glowing hydrogen, and of glowing matter giving a line so near the sodium line that in the case of a stellar spectrum it would, probably, not be possible to distinguish one from the other. Into the prominences there are thrown from time to time masses of glowing sodium, magnesium, and (in less degree) iron and other metallic vapours. Lastly, in that glorious appendage, the solar corona, which extends for hundreds of thousands of miles from the sun’s surface, there are enormous quantities of some element, whose nature is as yet unknown, showing under spectroscopic analysis the bright line which seems to have appeared in the spectrum of the flaming sun in the Swan.

This evidence seems to me to suggest that the intense heat which suddenly affected this star had its origin from without. At the same time, I cannot agree with Meyer and Klein in considering that the cause of the heat was either the downfall of a planetary mass on the star, or the collision of the star with a star-cloudlet, or nebula, traversing space in one direction while the star swept onwards in another. A planet could not very well come into final conflict with its sun at one fell swoop. It would gradually draw nearer and nearer, not by the narrowing of its path, but by the change of the path’s shape. The path would, in fact, become more and more eccentric; until, at length, at its point of nearest approach, the planet would graze its primary, exciting an intense heat where it struck, but escaping actual destruction that time. The planet would make another circuit, and again graze its sun, at or near the same part of the planet’s path. For several circuits this would continue, the grazes not becoming more effective each time, but rather less. The interval between them, however, would grow continually less and less. At last the time would come when the planet’s path would be reduced to the circular form, its globe touching its sun’s all the way round, and then the planet would very quickly be reduced to vapour, and partly burned up, its substance being absorbed by its sun. But all the successive grazes would be indicated to us by accessions in the star’s lustre, the period between each seeming outburst being only a few months at first, and becoming gradually less and less (during a long course of years, perhaps even of centuries), until the planet was finally destroyed. Nothing of this sort has happened in the case of any so-called new star.

As for the rush of a star through a nebulous mass, that is a theory which would scarcely be entertained by any one acquainted with the enormous distances separating the gaseous star-clouds properly called nebulae. There may be small clouds of the same sort scattered much more densely through space; but we have not a particle of evidence that this actually is the case. All we certainly know about star-cloudlets suggest that the distances separating them from each other are comparable with those which separate star from star, in which case the idea of a star coming into collision with a star-cloudlet, and still more the idea of this occurring several times in a century, is wild in the extreme.

On the whole, the theory seems more probable than any of these, that enormous flights of large meteoric masses travel around those stars which thus occasionally break forth in conflagration, such flights travelling on exceedingly eccentric paths, and requiring enormously long periods to complete each circuit of their vast orbits. In conceiving this, we are not imagining anything new. Such a meteoric flight would differ only in degree not kind from meteoric flights which are known to circle around our own sun. I am not sure, indeed, that it can be definitely asserted that our sun has no meteoric appendages of the same nature as those which, if this theory be true, excite to intense periodic activity the sun round which they circle. We know that comets and meteors are closely connected, every comet being probably (many certainly) attended by flights of meteoric masses. The meteors which produce the celebrated November showers of falling stars follow in the track of a comet invisible to the naked eye. May we not reasonably suppose, then, that those glorious comets which have not only been visible but conspicuous, shining even in the day-time, and brandishing round tails which, like that of the ’wonder in heaven, the great dragon,’ seemed to ‘draw the third part of the stars of heaven,’ are followed by much denser flights of much more massive meteors? Now some among these giant comets have paths which carry them very close to our sun. Newton’s comet, with its tail a hundred millions of miles in length, all but grazed the sun’s globe. The comet of 1843, whose tail, says Sir J. Herschel, ‘stretched half-way across the sky,’ must actually have grazed the sun, though but lightly, for its nucleus was within 80,000 miles of his surface, and its head was more than 160,000 miles in diameter. And these are only two among the few comets whose paths are known. At any time we might be visited by a comet mightier than either, travelling on an orbit intersecting the sun’s surface, followed by flights of meteoric masses enormous in size and many in number, which, falling on the sun’s globe with the enormous velocity corresponding to their vast orbital range and their near approach to the sun a velocity of some 360 miles per second would, beyond all doubt, excite his whole frame, and especially his surface regions, to a degree of heat far exceeding what he now emits.

We have had evidence of the tremendous heat to which the sun’s surface would be excited by the downfall of a shower of large meteoric masses. Carrington and Hodgson, on September 1, 1859, observed (independently) the passage of two intensely bright bodies across a small part of the sun’s surface the bodies first increasing in brightness, then diminishing, then fading away. It is generally believed that these were meteoric masses raised to fierce heat by frictional resistance. Now so much brighter did they appear, or rather did that part of the sun’s surface appear through which they had rushed, that Carrington supposed the dark glass screen used to protect the eye had broken, and Hodgson described the brightness of this part of the sun as such that the part shone like a brilliant star on the background of the glowing solar surface. Mark, also, the consequences of the downfall of those two bodies only. A magnetic disturbance affected the whole frame of the earth at the very time when the sun had been thus disturbed. Vivid auroras were seen not only in both hemispheres, but in latitudes where auroras are very seldom witnessed. ‘By degrees,’ says Sir J. Herschel, ’accounts began to pour in of great auroras seen not only in these latitudes, but at Rome, in the West Indies, in the tropics within eighteen degrees of the equator (where they hardly ever appear); nay, what is still more striking, in South America and in Australia where, at Melbourne, on the night of September 2, the greatest aurora ever seen there made its appearance. These auroras were accompanied with unusually great electro-magnetic disturbances in every part of the world. In many places the telegraph wires struck work. They had too many private messages of their own to convey. At Washington and Philadelphia, in America, the electric signal-men received severe electric shocks. At a station in Norway the telegraphic apparatus was set fire to; and at Boston, in North America, a flame of fire followed the pen of Bain’s electric telegraph, which writes down the message upon chemically prepared paper.’ Seeing that where the two meteors fell the sun’s surface glowed thus intensely, and that the effect of this accession of energy upon our earth was thus well marked, can it be doubted that a comet, bearing in its train a flight of many millions of meteoric masses, and falling directly upon the sun, would produce an accession of light and heat whose consequences would be disastrous? When the earth has passed through the richer portions (not the actual nuclei, be it remembered) of meteor systems, the meteors visible from even a single station have been counted by tens of thousands, and it has been computed that millions must have fallen upon the whole earth. These were meteors following in the train of very small comets. If a very large comet followed by no denser a flight of meteors, but each meteoric mass much larger, fell directly upon the sun, it would not be the outskirts but the nucleus of the meteoric train which would impinge upon him. They would number thousands of millions. The velocity of downfall of each mass would be more than 360 miles per second. And they would continue to pour in upon him for several days in succession, millions falling every hour. It seems not improbable that, under this tremendous and long-continued meteoric hail, his whole surface would be caused to glow as intensely as that small part whose brilliancy was so surprising in the observation made by Carrington and Hodgson. In that case, our sun, seen from some remote star whence ordinarily he is invisible, would shine out as a new sun, for a few days, while all things living on our earth, and whatever other members of the solar system are the abode of life, would inevitably be destroyed.

The reader must not suppose that this idea has been suggested merely in the attempt to explain outbursts of stars. The following passage from a paper of considerable scientific interest by Professor Kirkwood, of Bloomington, Indiana, a well-known American astronomer, shows that the idea had occurred to him for a very different reason. He speaks here of a probable connection between the comet of 1843 and the great sun-spot which appeared in June 1843. I am not sure, however, but that we may regard the very meteors which seem to have fallen on the sun on September 1, 1859, as bodies travelling in the track of the comet of 1843 just as the November meteors seen in 1867-8, 9, etc., until 1872, were bodies certainly following in the track of the telescopic comet of 1866. ‘The opinion has been expressed by more than one astronomer,’ he says, speaking of Carrington’s observation, ’that this phenomenon was produced by the fall of meteoric matter upon the sun’s surface. Now, the fact may be worthy of note that the comet of 1843 actually grazed the sun’s atmosphere about three months before the appearance of the great sun-spot of the same year. Had it approached but little nearer, the resistance of the atmosphere would probably have brought its entire mass to the solar surface. Even at its actual distance it must have produced considerable atmospheric disturbance. But the recent discovery that a number of comets are associated with meteoric matter, travelling in nearly the same orbits, suggests the inquiry whether an enormous meteorite following in the comet’s train, and having a somewhat less perihelion distance, may not have been precipitated upon the sun, thus producing the great disturbance observed so shortly after the comet’s perihelion passage.’

There are those, myself among the number, who consider the periodicity of the solar spots, that tide of spots which flows to its maximum and then ebbs to its minimum in a little more than eleven years, as only explicable on the theory that a small comet having this period, and followed by a meteor train, has a path intersecting the sun’s surface. In an article entitled ‘The Sun a Bubble,’ which appeared in the ‘Cornhill Magazine’ for October 1874, I remarked that from the observed phenomena of sun-spots we might be led to suspect the existence of some as yet undetected comet with a train of exceptionally large meteoric masses, travelling in a period of about eleven years round the sun, and having its place of nearest approach to that orb so close to the solar surface that, when the main flight is passing, the stragglers fall upon the sun’s surface. In this case, we could readily understand that, as this small comet unquestionably causes our sun to be variable to some slight degree in brilliancy, in a period of about eleven years, so some much larger comet circling around Mira, in a period of about 331 days, may occasion those alternations of brightness which have been described above. It may be noticed in passing, that it is by no means certain that the time when the sun is most spotted is the time when he gives out least light. Though at such times his surface is dark where the spots are, yet elsewhere it is probably brighter than usual; at any rate, all the evidence we have tends to show that when the sun is most spotted, his energies are most active. It is then that the coloured flames leap to their greatest height and show their greatest brilliancy, then also that they show the most rapid and remarkable changes of shape.

Supposing there really is, I will not say danger, but a possibility, that our sun may one day, through the arrival of some very large comet travelling directly towards him, share the fate of the suns whose outbursts I have described above, we might be destroyed unawares, or we might be aware for several weeks of the approach of the destroying comet. Suppose, for example, the comet, which might arrive from any part of the heavens, came from out that part of the star-depths which is occupied by the constellation Taurus then, if the arrival were so timed that the comet, which might reach the sun at any time, fell upon him in May or June, we should know nothing of that comet’s approach: for it would approach in that part of the heavens which was occupied by the sun, and his splendour would hide as with a veil the destroying enemy. On the other hand, if the comet, arriving from the same region of the heavens, so approached as to fall upon the sun in November or December, we should see it for several weeks. For it would then approach from the part of the heavens high above the southern horizon at midnight. Astronomers would be able in a few days after it was discovered to determine its path and predict its downfall upon the sun, precisely as Newton calculated the path of his comet and predicted its near approach to the sun. It would be known for weeks then that the event which Newton contemplated as likely to cause a tremendous outburst of solar heat, competent to destroy all life upon the surface of our earth, was about to take place; and, doubtless, the minds of many students of science would be exercised during that interval in determining whether Newton was right or wrong. For my own part, I have very little doubt that, though the change in the sun’s condition in consequence of the direct downfall upon his surface of a very large comet would be but temporary, and in that sense slight for what are a few weeks in the history of an orb which has already existed during thousands of millions of years? yet the effect upon the inhabitants of the earth would be by no means slight. I do not think, however, that any students of science would remain, after the catastrophe, to estimate or to record its effects.

Fortunately, all that we have learned hitherto from the stars favours the belief that, while a catastrophe of this sort may be possible, it is exceedingly unlikely. We may estimate the probabilities precisely in the same way that an insurance company estimates the chance of a railway accident. Such a company considers the number of accidents which occur among a given number of railway journeys, and from the smallness of the number of accidents compared with the largeness of the number of journeys estimates the safety of railway travelling. Our sun is one among many millions of suns, any one of which (though all but a few thousands are actually invisible) would become visible to the naked eye, if exposed to the same conditions as have affected the suns in flames described in the preceding pages. Seeing, then, that during the last two thousand years or thereabouts, only a few instances of the kind, certainly not so many as twenty, have been recorded, while there is reason to believe that some of these relate to the same star which has blazed out more than once, we may fairly consider the chance exceedingly small that during the next two thousand, or even the next twenty thousand years, our sun will be exposed to a catastrophe of the kind.

We might arrive at this conclusion independently of any considerations tending to show that our sun belongs to a safe class of system-rulers, and that all, or nearly all, the great solar catastrophes have occurred among suns of a particular class. There are, however, several considerations of the kind which are worth noting.

In the first place, we may dismiss as altogether unlikely the visit of a comet from the star-depths to our sun, on a course carrying the comet directly upon the sun’s surface. But if, among the comets travelling in regular attendance upon the sun, there be one whose orbit intersects the sun’s globe, then that comet must several times ere this have struck the sun, raising him temporarily to a destructive degree of heat. Now, such a comet must have a period of enormous length, for the races of animals now existing upon the earth must all have been formed since that comet’s last visit on the assumption, be it remembered, that the fall of a large comet upon the sun, or rather the direct passage of the sun through the meteoric nucleus of a large comet, would excite the sun to destructive heat. If all living creatures on the earth are to be destroyed when some comet belonging to the solar system makes its next return to the sun, that same comet at its last visit must have raised the sun to an equal, or even greater intensity of heat, so that either no such races as at present exist had then come into being, or, if any such existed, they must at that time have been utterly destroyed. We may fairly believe that all comets of the destructive sort have been eliminated. Judging from the evidence we have on the subject, the process of the formation of the solar system was one which involved the utilisation of cometic and meteoric matter; and it fortunately so chanced that the comets likely otherwise to have been most mischievous those, namely, which crossed the track of planets, and still more those whose paths intersected the globe of the sun were precisely those which would be earliest and most thoroughly used up in this way.

Secondly, it is noteworthy that all the stars which have blazed out suddenly, except one, have appeared in a particular region of the heavens the zone of the Milky Way (all, too, on one half of that zone). The single exception is the star in the Northern Crown, and that star appeared in a region which I have found to be connected with the Milky Way by a well-marked stream of stars, not a stream of a few stars scattered here and there, but a stream where thousands of stars are closely aggregated together, though not quite so closely as to form a visible extension of the Milky Way. In my map of 324,000 stars this stream can be quite clearly recognised; but, indeed, the brighter stars scattered along it form a stream recognisable with the naked eye, and have long since been regarded by astronomers as such, forming the stars of the Serpent and the Crown, or a serpentine streak followed by a loop of stars shaped like a coronet. Now the Milky Way, and the outlying streams of stars connected with it, seem to form a region of the stellar universe where fashioning processes are still at work. As Sir W. Herschel long since pointed out, we can recognise in various parts of the heavens various stages of development, and chief among the regions where as yet Nature’s work seems incomplete, is the Galactic zone especially that half of it where the Milky Way consists of irregular streams and clouds of stellar light. As there is no reason for believing that our sun belongs to this part of the galaxy, but on the contrary good ground for considering that he belongs to the class of insulated stars, few of which have shown signs of irregular variation, while none have ever blazed suddenly out with many hundred times their former lustre, we may fairly infer a very high degree of probability in favour of the belief that, for many ages still to come, the sun will continue steadily to discharge his duties as fire, light, and life of the solar system.