By J. E. GORE, F.R.A.S., Honorary Associate and Vice-President of the
Liverpool Astronomical Society.
If we look up at the starry heavens on a clear, moonless night, all seems
still, lifeless, and devoid of energy and motion. All of us are--or at
least should be--familiar with the apparent diurnal motion of the star
sphere, caused by the actual rotation of the earth on its axis, and with
the slower annual motion, due to the earth's revolution round the sun,
which brings different constellations into view at different seasons of
the year. These motions, due to the great and universal law of
gravitation, discovered and so ably expounded by the famous Sir Isaac
Newton, are of course wonderful and orderly in their regularity, and bear
silent testimony to the amazing power, majesty, and goodness of a great
and glorious Creator. There are, however, other motions and changes, even
still more wonderful, going on in the depths of space, which, though
unperceived by the ordinary observer, have been revealed to the eye and
contemplation of the astronomer by the accurate instruments and methods of
research which modern science has placed at his disposal. Some accounts of
these marvelous discoveries may prove of interest to the reader. The
"fixed stars" are so called because they apparently hold a fixed position
with reference to each other on the concave surface of the celestial
vault, and do not, as far as the unaided eye can judge, change their
relative positions as the planets do. Many stars have, however, what is
technically called a "proper motion," which, though of course very minute,
and only to be detected by the aid of refined and accurate instruments,
yet accumulate in the course of ages, and sensibly alter their position in
the sky. The largest "proper motion" hitherto detected (about seven
seconds of arc per annum) is that of a small star in the constellation
Ursa Major, known to astronomers as No. 1830 of Groonbridge's catalogue.
It has been calculated that this star is rushing through space with the
amazing and almost inconceivable velocity of 200 miles per second!--a
velocity which would carry it from the earth to the sun in about 5-1/2 days
and to the moon in 20 minutes! The well-known double star 61 Cygni has a
proper motion of about five seconds of arc per annum, both components
moving through space together. This is, as far as yet known, the nearest
star to the earth in the northern hemisphere. Its parallax, as determined
by Sir R. S. Ball, is 0.4676 of a second of arc, and by Prof. Pritchard
(by photography) 0.43 of a second. Taking the mean of these values, its
distance from the earth would be about 460,000 times the earth's mean
distance from the sun, and its actual velocity about 33 miles per second.
This is, of course, the motion at right angles to the line of sight, but
as it may also have a motion _in_ the line of sight, either to or from the
eye, its real velocity is probably greater than this. The remarkable
triple star 40 Eridani has a proper motion of four seconds annually. The
components are a fourth magnitude star accompanied by a distant double
companion which is a binary (or revolving double star), and accompanies
the bright star in its flight through space. There are two other faint and
distant companions which do not partake in the motion of the ternary star.
In the year 1864 the bright star was situated to the east of a line
joining these faint companions, but owing to its large proper motion it is
now to the west of them. In the case of the triple star Struve 1516, one
of the companions, which was to the west of the primary star in 1831, is,
owing to the proper motion of the bright star, now to the east of it.
Prof. Asaph Hall has found a parallax for 40 Eridani of 0.223 of a second.
This, combined with the observed proper motion, indicates an actual
velocity of about 54 miles per second. The star Mu Cassiopeiae has also a
large proper motion. This star, about 4,000 years ago, must have been
close to Alpha Cassiopeiae, and might have been so seen by the ancient
astronomers. The proper motion of the bright star Arcturus is so
considerable that in the course of about 30,000 years it will be near the
equator, and about 10 deg. to the north of the bright star Spica, from which
it is at present separated by over 30 deg. These motions are of course those
which take place across the face of the sky. There are, however, motions
in the line of sight--both toward and from the eye--which have of late
years been revealed to us by the spectroscope, that wonderful instrument
of modern scientific research, by the aid of which several new metals have
been discovered, and which has been found so useful in chemical analysis,
and even in the manufacture of steel by the Bessemer process. Some years
since, Dr. Huggins, the eminent spectroscopist, found that the bright star
Sirius, "the monarch of the skies," was receding from the earth at the
rate of about 20 miles a second. Later observations at Greenwich
Observatory showed that this motion was gradually diminishing, and within
the last few years it has been found that the motion of recession has been
actually changed into a motion of approach, showing that this giant sun is
probably traveling in a mighty orbit round some as yet unknown center of
gravity.
From a consideration of stellar proper motions, it has been concluded that
the sun--and therefore the whole solar system--is moving through space.
Recent investigations make the velocity of translation about 19 miles per
second (30 kilometers). The Greenwich observations place the "apex of the
solar motion" (as the point toward which the sun is moving is called)
between Rho and Sigma Cygni, while Dr. Huggins' results fix a point near
Beta Cephei. Both these points are near the Milky Way.
There are other startling changes which have occasionally taken place
among the stars, and which must be looked upon almost in the light of
catastrophes. At rare intervals in the history of astronomy "temporary" or
"new" stars have suddenly blazed out in the heavens which were previously
either unknown to astronomers, or else were invisible, except in the
telescope. Some of these were of great brilliancy. In A.D. 173 a bright
star is recorded in the Chinese annals as having appeared between Alpha
and Beta Centauri (two bright stars in the southern hemisphere). It
remained visible for seven or eight months, and is described as resembling
"a large bamboo mat" (!)--a not very lucid description. It is worthy of
remark that there exists at the present time, close to the spot indicated,
an interesting variable star, which may possibly be identical with the
bright star of the second century. Perhaps the most remarkable of these
wonderful objects was that observed by the famous Tycho Brahe in 1572, in
Cassiopeia, and called the "Pilgrim." It was so brilliant that it rivaled
the planet Venus at its brightest, and was visible at noonday. It remained
visible for over a year and then disappeared.
A small star close to its recorded position has been observed in recent
years, and as it is thought to be slightly variable in its light, it may
possibly be identical with the long lost star of Tycho Brahe. Another new
star of almost equal brilliancy was observed in October, 1604, in
Ophiuchus, a few degrees southeast of the star Eta Ophiuchi. The planets
Mars, Jupiter, and Saturn were close together in this vicinity, and one
evening Mostlin, a pupil of Kepler's, remarked that a new and very
brilliant star had joined the group. When first seen it was white, and
exceeded in brightness Mars and Jupiter, and was even thought to rival
Venus in splendor! It gradually diminished, however, and in six months was
not equal in luster to Saturn; in March, 1606, it had entirely
disappeared. In 1670 a star of the third magnitude was observed by Anthelm
near Beta Cygni. It remained visible for about two years, and increased
and diminished several times before it finally disappeared. Flamsteed's
star, No. 11 of Vulpecula, has been supposed to be identical with
Anthelm's star, but Baily could not find that such a star exists. A small
star has, however, been observed at Greenwich within one minute of arc of
the place assigned to the temporary star by Picard's observations.
Variability has been suspected in this faint star, and according to Hind
it has a hazy, ill-defined appearance about it, which may perhaps suggest
that it may be a small planetary nebula, similar to Schmidt's new star of
1876 in Cygnus. A small new star was observed by Hind in Ophiuchus on
April 28, 1848. When first noticed it was about the fifth magnitude. It
afterward rose to about fourth magnitude, but very soon faded away, and,
although still visible in the telescope, has become very faint in recent
years. A new star of seventh magnitude was found by Pogson on May 28,
1860, in the well-known star cluster known as 80 Messier in Scorpio. The
light of the star when first seen obscured the light of the nebula. On
June 10 the star had nearly disappeared, and the nebula was again seen
shining with great brilliancy.
A very interesting temporary star--known as the "Blaze Star"--suddenly
appeared in Corona Borealis in May, 1866. It was first seen by the late
Mr. Birmingham, of Tuam, Ireland, on the night of May 12, when it was of
the second magnitude and equal in brightness to Alphecca, the brightest
star in the well-known "Coronet." It must have made its appearance very
suddenly, for Dr. Schmidt, the director of the Athens observatory, stated
that he was observing this region of the heavens a few hours previously,
and noticed nothing unusual. It rapidly diminished in brightness, and on
May 24 of the same year was reduced to nearly the ninth magnitude. It was
soon discovered that the star had been previously observed, and its place
registered by the great German astronomer, Argelander, as of magnitude 9-1/2,
so that it is possibly a variable star of irregular period and fitful
variability. When near its maximum brilliancy, its light was examined by
Dr. Huggins with the spectroscope, which showed the bright lines of
incandescent hydrogen gas in addition to the ordinary stellar spectrum.
This implies that the great increase in its light was due to a sudden
outburst of hydrogen in the star's atmosphere. Some observers remarked
that when viewed with the naked eye it decidedly twinkled more than other
stars in the neighborhood, which rendered a correct estimate of its
relative brightness somewhat difficult. During the years 1866 to 1876,
Schmidt detected variations of light which seemed to show a period of
about 94 days, and these observations were confirmed by Schonfeld.
On the evening of November 24, 1876, the late Dr. Schmidt, of Athens,
discovered a new star of the third magnitude, near Rho Cygni, in a spot
where he was certain that no bright star was visible four nights
previously. When first seen, it was somewhat brighter than Eta Pegasi. It
did not, however, remain long at this degree of brightness, but rapidly
decreased, and on November 30 had faded to fifth magnitude. It afterward
diminished very regularly, and in September, 1885, was estimated only
fifteenth magnitude with the 15-1/2 inch refractor of Mr. Wigglesworth's
observatory. The star was examined with the spectroscope a few days after
its discovery, and showed bright lines similar to the "Blaze Star" in the
Northern Crown. One of these bright lines was believed to be identical
with Kirchhoff's No. 1474, which has been observed in the spectrum of the
solar corona during total eclipses of the sun. This star would seem to be
quite new, as there is no star in any of the catalogues in its position.
In September, 1877, it was examined with the spectroscope at Lord
Crawford's observatory, and its light was found to be almost entirely
monochromatic (of only one color), showing that the star "had changed into
a planetary nebula of small angular diameter" (!)
In August, 1885, a star of about seventh magnitude made its appearance
close to the nucleus of the Great Nebula in Andromeda--a well-known object
visible to the naked eye, and which has been well called "the Queen of the
Nebulae." The new star was independently discovered by several observers
toward the end of August, but seems to have been first certainly seen by
Mr. T. W. Ward, of Belfast, on August 19, at 11 P.M. At Greenwich
observatory the spectrum of the new star was found "of precisely the same
character as that of the nebula, _i. e._, it was perfectly continuous, no
lines, either bright or dark, being visible, and the red end was wanting."
Dr. Huggins, however, on September 9, thought he could see from three to
five bright lines in its spectrum. The star gradually faded away, and on
February 7, 1886, was estimated only sixteenth magnitude in the 26 inch
refractor of the naval observatory at Washington. From a series of
measures by Prof. Asaph Hall he found "no certain indications of any
parallax," so that evidently the star and the nebula, in which it probably
lies, are situated at an immense distance from the earth. Prof. Seeliger
has investigated the decrease in light of the star on the hypothesis that
it was a cooling body, which had been suddenly raised to an intense heat
by the shock of a collision, and finds a fair agreement between theory and
observation. Anwers points out the similarity between this outburst and
the new star of 1860 in the cluster 80 Messier, and thinks it very
probable that both phenomena were due to physical changes in the nebulae in
which they occurred.
With reference to the colors of the stars, some of the red stars have been
suspected to vary in color. The bright star Sirius is supposed--from the
description of it by ancient astronomers--to have been originally red, but
this seems very doubtful. The Persian astronomer Al Sufi, in his
"Description of the Heavens," written in the tenth century, describes the
well-known variable star Algol distinctly as a red star. It is now white,
and this is perhaps the best attested instance on record of change of
color in a bright star.--_Naturalists' Monthly._