attracted to the words of another observer more experienced than M.
Cornu, who has not only expressed the same opinion which I entertain
respecting M. Cornu’s ill-advised remark, but has illustrated in a
very practical way, and in this very case, how science gains from
commentary and theory upon observed facts. Herr Vögel considers “that
the fear that an hypothesis” (he, also, means a theory here) “might do
harm to science is only justifiable in very rare cases: in most cases
it will further science. In the first place, it draws the attention of
the observer to things which but for the hypothesis might have been
neglected. Of course if the observer is so strongly influenced that
in favour of an hypothesis he sees things which do not exist—and
this may happen sometimes—science may for a while be arrested in its
progress, but in that case the observer is far more to blame than
the author of the hypothesis. On the other hand, it is very possible
that an observer may, involuntarily, arrest the progress of science,
even without originating an hypothesis, by pronouncing and publishing
sentences which have a tendency to diminish the general interest in a
question, and which do not place its high significance in the proper
light.” (This is very neatly put.) He is “almost inclined to think that
such an effect might follow from the reading of M. Cornu’s remark, and
that nowhere better than in the present case, where in short periods
colossal changes showed themselves occurring upon a heavenly body,
might the necessary data be obtained for drawing useful conclusions,
and tests be applied to those hypotheses which have been ventured
with regard to the condition of heavenly bodies.” It was, as we shall
presently see, in thus collecting data and applying tests, that Vögel
practically illustrated the justice of his views.
The star which shone out in the Northern Crown in May, 1866, would seem
to have grown to its full brightness very quickly. It is not necessary
that I should here consider the history of the star’s discovery; but
I think all who have examined that history agree in considering that
whereas on the evening of May 12, 1866, a new star was shining in the
Northern Crown with second-magnitude brightness, none had been visible
in the same spot with brightness above that of a fifth-magnitude
star twenty-four hours earlier. On ascertaining, however, the place
of the new star, astronomers found that there had been recorded in
Argelander’s charts and catalogue a star of between the ninth and tenth
magnitude in this spot. The star declined very rapidly in brightness.
On May 13th it appeared of the third magnitude; on May 16th it had
sunk to the fourth magnitude; on the 17th to the fifth; on the 19th to
the seventh; and by the end of the month it shone only as a telescopic
star of the ninth magnitude. It is now certainly not above the tenth
magnitude.
Examined with the spectroscope, this star was found to be in an
abnormal condition. It gave the rainbow-tinted streak crossed by dark
lines, which is usually given by stars (with minor variations, which
enable astronomers to classify the stars into several distinct orders).
But superposed upon this spectrum, or perhaps we should rather say
shining through this spectrum, were seen four brilliant lines, two
of which certainly belonged to glowing hydrogen. These lines were so
bright as to show that the greater part of the light of the star at
the time came from the glowing gas or gases giving these lines. It
appeared, however, that the rainbow-tinted spectrum on which these
lines were seen was considerably brighter than it would otherwise have
been, in consequence of the accession of heat indicated by and probably
derived from the glowing hydrogen.
Unfortunately, we have not accordant accounts of the changes which the
spectrum of this star underwent as the star faded out of view. Wolf
and Rayet, of the Paris Observatory, assert that when there remained
scarcely any trace of the continuous spectrum, the four bright lines
were still quite brilliant. But Huggins affirms that this was not the
case in his observations; he was “able to see the continuous spectrum
when the bright lines could be scarcely distinguished.” As the bright
lines certainly faded out of view eventually, we may reasonably assume
that the French observers were prevented by the brightness of the lines
from recognizing the continuous spectrum at that particular stage of
the diminution of the star’s light when the continuous spectrum had
faded considerably but the hydrogen lines little. Later, the continuous
spectrum ceased to diminish in brightness, while the hydrogen lines
rapidly faded. Thereafter the continuous spectrum could be discerned,
and with greater and greater distinctness as the hydrogen lines faded
out.
Now, in considering the meaning of the observed changes in the
so-called “new star,” we have two general theories to consider.
One of these theories is that to which Dr. Huggins would seem to have
inclined, though he did not definitely adopt it—the theory, namely,
that in consequence of some internal convulsion enormous quantities of
hydrogen and other gases were evolved, which in combining with some
other elements ignited on the surface of the star, and thus enveloped
the whole body suddenly in a sheet of flame.
“The ignited hydrogen gas in burning produced the light corresponding
to the two bright bands in the red and green; the remaining bright
lines were not, however, coincident with those of oxygen, as might have
been expected. According to this theory, the burning hydrogen must have
greatly increased the heat of the solid matter of the photosphere and
brought it into a state of more intense incandescence and luminosity,
which may explain how the formerly faint star could so suddenly assume
such remarkable brilliance; the liberated hydrogen became exhausted,
the flame gradually abated, and with the consequent cooling the
photosphere became less vivid, and the star returned to its original
condition.”
According to the other theory, advanced by Meyer and Klein, the
blazing forth of this new star may have been occasioned by the violent
precipitation of some great mass, perhaps a planet, upon a fixed star,
“by which the momentum of the falling mass would be changed into
molecular motion,” and result in the emission of light and heat.
“It might even be supposed that the new star, through its rapid motion,
may have come in contact with one of the nebulæ which traverse in great
numbers the realms of space in every direction, and which from their
gaseous condition must possess a high temperature; such a collision
would necessarily set the star in a blaze, and occasion the most
vehement ignition of its hydrogen.”
If we regard these two theories in their more general aspect,
considering one as the theory that the origin of disturbance was within
the star, and the other as the theory that the origin of disturbance
was outside the star, they seem to include all possible interpretations
of the observed phenomena. But, as actually advanced, neither seems
satisfactory. The sudden pouring forth of hydrogen from the interior,
in quantities sufficient to explain the outburst, seems altogether
improbable. On the other hand, as I have pointed out elsewhere, there
are reasons for rejecting the theory that the cause of the heat which
suddenly affected this star was either the downfall of a planet on
the star or the collision of the star with a star-cloudlet or nebula,
traversing space in one direction, while the star rushed 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 the sun,
at or near the same part of the planet’s path. For several circuits
this would continue, the grazes not becoming more and 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 the 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 successive grazes would be indicated to
us by accessions of lustre, the period between each seeming outburst
being only a few months at first, and gradually becoming 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 nebulæ. There may be small clouds of the
same sort scattered much more freely through space; but we have not a
particle of evidence that this is actually the case. All we certainly
_know_ about star-cloudlets suggests 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.
But while thus advancing objections, which seem to me irrefragable,
against the theory that either a planet or a nebula (still less another
small star) had come into collision with the orb in Corona which shone
out so splendidly for a while, I advanced another view which seemed
to me then and seems now to correspond well with phenomena, and to
render the theory of action from without on the whole preferable to the
theory of outburst from within. I suggested that, far more probably,
an enormous flight of large meteoric masses travelling around the
star had come into partial collision with it in the same way that the
flight of November meteors comes into collision with our earth thrice
in each century, and that other meteoric flights may occasionally come
into collision with our sun, producing the disturbances which occasion
the sun-spots. As I pointed out, in conceiving this we are imagining
nothing new. A meteoric flight capable of producing the suggested
effects would differ only in kind from meteoric flights which are known
to circle around our own sun. The meteors which produce the November
displays of falling stars follow in the track of a comet barely visible
to the naked eye.
“May we not reasonably assume that those glorious comets which have not
only been visible but conspicuous, shining even in the day-time, and
brandishing around 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?
Some of 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 John 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 in 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 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.”
This theory corresponds far better also with observed facts than the
theory of Meyer and Klein, in other respects than simply in antecedent
probability. It can easily be shown that if a planet fell upon a
sun in such sort as to become part of his mass, or if a nebula in a
state of intense heat excited the whole frame of a star to a similar
degree of heat, the effects would be of longer duration than the
observed accession of heat and light in the case of all the so-called
“new stars.” It has been calculated by Mr. Croll (the well-known
mathematician to whom we owe the most complete investigations yet made
into the effect of the varying eccentricity of the earth’s orbit on the
climate of the earth) that if two suns, each equal in mass to one-half
of our sun, came into collision with a velocity of 476 miles per
second, light and heat would be produced which would cover the present
rate of the sun’s radiation for fifty million years. Now although it
certainly does not follow from this that such a collision would result
in the steady emission of so much light and heat as our sun gives out,
for a period of fifty million years, but is, on the contrary, certain
that there would be a far greater emission at first and a far smaller
emission afterwards, yet it manifestly must be admitted that such a
collision could not possibly produce so short-lived an effect as we see
in the case of every one of the so-called new stars. The diminution
in the emission of light and heat from the maximum to one-half the
maximum would not occupy fifty millions of years, or perhaps even five
million or five hundred thousand years; but it would certainly require
thousands of years; whereas we have seen that the new stars in the
Crown and in the Swan have lost not one-half but ninety-nine hundredths
of their maximum lustre in a few months.
This has been urged as an objection even to the term star as applied to
these suddenly appearing orbs. But the objection is not valid; because
there is no reason whatever for supposing that even our own sun might
not be excited by the downfall of meteoric or cometic matter upon it
to a sudden and short-lasting intensity of splendour and of heat. Mr.
Lockyer remarks that, if any star, properly so called, were to become
a “a world on fire,” or “burst into flames,” or, in less poetical
language, were to be driven either into a condition of incandescence
absolutely, or to have its incandescence increased, there can be little
doubt that thousands or millions of years would be necessary for the
reduction of its light to its original intensity. This must, however,
have been written in forgetfulness of some facts which have been
ascertained respecting our sun, and which indicate pretty clearly that
the sun’s surface might be roused to a temporary intensity of splendour
and heat without any corresponding increase in the internal heat, or in
the activity of the causes, whatever they may be, to which the sun’s
_steady_ emissions of light and heat are due.
For instance, most of my readers are doubtless familiar with the
account (an oft-told tale, at any rate) of the sudden increase in
the splendour of a small portion of the sun’s surface on September
1, 1859, observed by two astronomers independently. The appearances
described corresponded exactly with what we should expect if two large
meteoric masses travelling side by side had rushed, with a velocity
originally amounting to two or three hundred miles per second, through
the portions of the solar atmosphere lying just above, at, and just
below the visible photosphere. The actual rate of motion was measured
at 120 miles per second as the minimum, but may, if the direction of
motion was considerably inclined to the line of sight, have amounted
to more than 200 miles per second. The effect was such, that the parts
of the sun thus suddenly excited to an increased emission of light and
heat appeared like bright stars upon the background of the glowing
photosphere itself. One of the observers, Carrington, supposed for a
moment that the dark glass screen used to protect the eye had broken.
The increase of splendour was exceedingly limited in area, and lasted
only for a few minutes—fortunately for the inhabitants of earth. As
it was, the whole frame of the earth sympathized with the sun. Vivid
auroras were seen, not only in both hemispheres, but in latitudes where
auroras are seldom seen. They were accompanied by unusually great
electro-magnetic disturbances.
“In many places,” says Sir J. Herschel, “the telegraph wires struck
work. At Washington and Philadelphia, the electric signalmen 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.”
We see, then, that most certainly the sun can be locally excited to
increased emission of light and heat, which nevertheless may last but
for a very short time; and we have good reason for believing that the
actual cause of the sudden change in his condition was the downfall
of meteoric matter upon a portion of his surface. We may well believe
that, whatever the cause may have been, it was one which might in the
case of other suns, or even in our sun’s own case, affect a much larger
portion of the photosphere. If this happened there would be just
such an accession of splendour as we recognize in the case of the new
stars. And as the small local accession of brilliancy lasted only a few
minutes, we can well believe that an increase of surface brilliancy
affecting a much larger portion of the photosphere, or even the entire
photosphere, might last but for a few days or weeks.
All that can be said in the way of negative evidence, so far as our
own sun is concerned, is that we have no reason for believing that
our sun has, at any time within many thousands of years, been excited
to emit even for a few hours a much greater amount of light and heat
than usual; so that it has afforded no direct evidence in favour of
the belief that other suns may be roused to many times their normal
splendour, and yet very quickly resume that usual lustre. But we know
that our sun, whether because of his situation in space, or of his
position in time (that is, the stage of solar development to which he
has at present attained), belongs to the class of stars which shine
with steady lustre. He does not vary like Betelgeux, for example, which
is not only a sun like him as to general character, but notably a
larger and more massive orb. Still less is he like Mira, the Wonderful
Star; or like that more wonderful variable star, Eta Argûs, which at
one time shines with a lustre nearly equalling that of the bright
Sirius, and anon fades away almost into utter invisibility. He _is_ a
variable sun, for we cannot suppose that the waxing and waning of the
sun-spot period leaves his lustre, as a whole, altogether unaffected.
But his variation is so slight that, with all ordinary methods of
photometric measurement by observers stationed on worlds which circle
around other suns, it must be absolutely undiscernible. We do not,
however, reject Betelgeux, or Mira, or even Eta Argûs, from among stars
because they vary in lustre. We recognize the fact that, as in glory,
so in condition and in changes of condition, one star differeth from
another.
Doubtless there are excellent reasons for rejecting the theory that a
massive body like a planet, or a nebulous mass like those which are
found among the star-depths (the least of which would exceed many
times in volume a sphere filling the entire space of the orbit of
Neptune), fell on some remote sun in the Northern Crown. But there are
no sufficient reasons for rejecting or even doubting the theory that
a comet, bearing in its train a flight of many millions of meteoric
masses, falling directly upon such a sun, might cause it to shine
with many times its ordinary lustre, but only for a short time, a few
months or weeks, or a few days, or even hours. In the article entitled
“Suns in Flames,” in my “Myths and Marvels of Astronomy,” before the
startling evidence recently obtained from the star in Cygnus had
been thought of, I thus indicated the probable effects of such an
event:—“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 trains 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 abodes of life, would inevitably be destroyed.”
There are, indeed, reasons for believing, not only, as I have already
indicated, that the outburst in the sun was caused by the downfall of
meteoric masses, but that those masses were following in the train of
a known comet, precisely as the November meteors follow in the train of
Tempel’s comet (II., 1866). For we know that November meteoric displays
have been witnessed for five or six years after the passage of Tempel’s
comet, in its thirty-three year orbit, while the August meteoric
displays have been witnessed fully one hundred and twenty years
after the passage of their comet (II., 1862).[15] Now only sixteen
years before the solar outburst witnessed by Carrington and Hodgson,
a magnificent comet had passed even closer to the sun than either
Tempel’s comet or the second comet of 1862 approached the earth’s
orbit. That was the famous comet of the year 1843. Many of us remember
that wonderful object. I was but a child myself when it appeared, but
I can well remember its amazing tail, which in March, 1843, stretched
half-way across the sky.
“Of all the comets on record,” says Sir J. Herschel, “that approached
nearest the sun; indeed, it was at first supposed that it had actually
grazed the sun’s surface, but it proved to have just missed by an
interval of not more than 80,000 miles—about a third of the distance
of the moon from the earth, which (in such a matter) is a very close
shave indeed to get clear off.”
We can well believe that the two meteors which produced the remarkable
outburst of 1859 may have been stragglers from the main body following
after that glorious comet. I do not insist upon the connection. In
fact, I rather incline to the belief that the disturbance in 1859,
occurring as it did about the time of maximum sun-spot frequency, was
caused by meteors following in the train of some as yet undiscovered
comet, circuiting the sun in about eleven years, the spots themselves
being, I believe, due in the main to meteoric downfalls. There is
greater reason for believing that the great sun-spot which appeared
in June, 1843, was caused by the comet which three months before had
grazed the sun’s surface. As Professor Kirkwood, of Bloomington,
Indiana, justly remarks, had this comet approached a little nearer,
the resistance of the solar atmosphere would probably have brought
the comet’s 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.
Let us consider now the evidence obtained from the star in Cygnus,
noting especially in what points it resembles, and in what points it
differs from, the evidence afforded by the star in the Crown.