eighth magnitude, I made an examination of the stars shown on Harding’s
charts to that magnitude, in a zone of 30° in width—15° degrees on each
side of the Equator—and found a marked increase in the number of stars
where the zone crossed the Milky Way. The numbers per hour of Right
Ascension varied from a minimum of 275 (hours I. and II.) to maxima of
601 in the Milky Way in Monoceros, and 611 in the Galaxy in Serpens and
Aquila. A valuable investigation by the late Mr. Proctor went further
still. He plotted all the stars shown in the charts of Argelander’s
_Durchmusterung_, which contains stars to 9½ or 10th magnitude. In this
remarkable chart the course of the Milky Way is clearly defined by a
marked increase of stellar density. Proctor says: “In the very regions
where the Herschelian gauges showed the minutest telescopic stars to be
most crowded, my chart of 324,198 stars shows the stars of the higher
orders (down to the eleventh magnitude) to be so crowded that, by their
mere aggregation within the mass, they show the Milky Way with all its
streams and clusterings. This evidence, I venture to affirm, is
altogether decisive as to the main question, whether large and small
stars are really intermixed in many regions of space, or whether the
small stars are excessively remote. It is utterly impossible that
excessively remote stars could seem to be clustered exactly where
relatively near stars are richly spread. This might happen, no doubt, in
a single instance; but that it could be repeated over and over again, so
as to account for all the complicated features seen in my chart of
324,198 stars, I maintain to be utterly incredible.”[146]
From a careful examination of the Milky Way in Aquila and Cygnus, Mr.
Easton finds that “(1) In the zones considered, the distribution of
stars down to 9·5 magnitude corresponds to the greater or less intensity
of galactic light. (2) There is a real correspondence of the general
outlines of the galactic forms with the distribution of 11 magnitude
stars, and with those of stars between 10 and 15 magnitude. (3) Thus, in
general, for the zones considered, the faint stars which form the Milky
Way are thickly or sparsely scattered in respectively the same regions
as the stars in Argelander’s last class; it follows, therefore, with a
great degree of probability, that there is a real connexion between the
distribution of 9 and 10 magnitude stars and that of the very faint
stars of the Milky Way. Consequently, the very faint stars are at a
distance which does not greatly exceed that of 9–10 magnitude stars. If
stars of 13–15 magnitude were at their theoretical distance, there would
be no reason why they should have the same apparent distribution in
galactic latitude and longitude as 9–10 magnitude stars separated from
them by enormous intervals.”[147]
There are some regions in both hemispheres especially rich in naked eye
stars. Of these the following may be mentioned in the Northern
Hemisphere:—the region including the Pleiades, and Hyades in Taurus, the
Northern portion of Orion, and the adjoining part of Gemini, the
constellation Lyra, the northern portion of Cygnus, Cassiopeia’s Chair,
and Coma Berenices. In the Southern Hemisphere there are several rich
spots. A rich region extends from Canis Major to the Southern Cross, and
nearly coincides with the course of the Milky Way. The richest spot of
all, and perhaps the richest in the whole heavens in naked eye
stars—with exception of the Pleiades—is that including the Southern
Cross. This spot has an average of three stars to five square degrees,
and if the whole heavens were as richly studded with stars there would
be about 24,000 visible to the naked eye! The poverty of the adjoining
“coal sack” is very remarkable. Another rich spot surrounds the variable
star Eta Argûs, and the great nebula in Argo. There is another rich spot
in the constellation Hydrus, not far from the greater Magellanic Cloud,
and another will be found in Centaurus and Lupus, with its centre about
Alpha of the latter constellation. According to Gould’s maps of the
Southern Hemisphere, the richest region in stars down to the seventh
magnitude is the southern portion of that part of the constellation
Argo, known as Puppis.
In contrast to these rich regions, and in many cases closely adjoining
them, are some barren regions, very poor in naked eye stars. For
example, closely following the rich spot in Cassiopeia and between Iota
Cassiopeiæ and Eta Persei is a remarkably poor spot, where a space of
some sixty square degrees does not contain a single star brighter than
the sixth magnitude! There is another poor region south of Alpha Hydræ,
and another in the southern portion of the constellation Cetus.
A region of considerable extent, remarkably deficient in bright stars,
will be noticed in the Northern Hemisphere. This comparatively barren
region, which contains no star brighter than the fourth magnitude, is
bounded by Cepheus, Cassiopeia, Perseus, Auriga, Gemini, Ursa Major,
Draco, and Ursa Minor, and forms a conspicuous feature in the
north-eastern portion of the sky in the early winter evenings. It will
be noticed that the surrounding constellations all contain bright stars.
Whether the apparent crowding of stars in certain regions of the heavens
is caused by a real proximity in space, or whether it is merely due to
their being placed accidentally in the line of sight, is a question
difficult to determine. In the case of star clusters, and especially the
globular clusters, there is a high mathematical probability, amounting
almost to absolute certainty, that they are comparatively close
together, but in groups scattered over a considerable area, like those
referred to above, the probability in favour of proximity is not so
great. As we know the distance of so few stars from the earth, it is
impossible to say whether the crowding is real or only apparent, but the
probability seems to be that it is to some extent real.
A tendency to an arrangement of stars in streams was pointed out by
Proctor in his “Universe and the Coming Transits.” This tendency to
stream formation may be noticed on a large scale among the naked eye
stars, for example, in Pisces, Scorpio, the River Eridanus, Aquarius,
and the festoon of stars in Perseus. In some of these cases, of course,
the stars are so far apart that the formation may be more apparent than
real, but the tendency can also be clearly recognised among the fainter
stars, and even among those only visible in telescopes and stellar
photographs. This tendency to run in streams is well marked on the
photographs taken at the Paris Observatory, and on those taken by
Professor Barnard, Dr. Max Wolf, and others. It is a suggestive fact
that these star streams are also very noticeable in star clusters, where
there can be little or no doubt of a physical connexion between the
component stars. With reference to a photograph of the southern portion
of Aquila taken by Dr. Max Wolf in July, 1892, the late Mr. Ranyard,
remarked: “Some of the streams of fainter stars in this region are very
striking, and must convince the most sceptical of their reality. It is
possible to draw an arc of a circle through any three stars, and a conic
section through any five; but where we find ten or twenty stars falling
into line, not once, but in many cases, and that there is a curious
similarity between the strange curves and branching streams which these
phalanges of stars mark out on the heavens, there is no room left for
doubt that the mind is not being led away by a tendency of the
imagination similar to that which finds faces in the fire, or sees a man
carrying sticks on the face of the moon. If it is proved that a group of
stars is arranged in line or marshalled in any order, it would follow
that the individuals of the group must be actually as well as apparently
close to one another, and that they form some kind of system, having all
of them had a common origin, or been subject to some common
influence.”[148]
The great majority of the star clusters are found along the course of
the Milky Way, while the irresolvable nebulæ seem to congregate towards
the poles of the galactic zone.
Dr. Gould is of opinion that “a belt or stream of bright stars appears
to girdle the heavens very nearly in a great circle, which intersects
the Milky Way at about the points of its highest declination, and forms
with it an angle not far from 20°; the southern node being near the
margin of the Cross, and the northern in Cassiopeia.” According to
Gould, this belt covers Orion, Canis Major, Columba, Puppis, Carina, the
Southern Cross, Centaurus, Lupus, and the head of Scorpion in the
Southern Hemisphere, its northern course being indicated by the
brightest stars in Taurus, Perseus, Cassiopeia, Cepheus, Cygnus, and
Lyra. Dr. Gould considers that our sun may possibly be a member of this
belt of stars, which perhaps numbers less than 500, and which constitute
“a small cluster, distinct from the vast organisation of that which
forms the Milky Way, and of a flattened and somewhat bifid form. The
southern portion of this supposed stream of bright stars had been
previously recognised by Sir John Herschel, who says in his ‘Cape
Observations,’ (p. 385), ‘It is about this region, or, perhaps, somewhat
earlier, in the interval between η Argus and α Crucis, that the galactic
circle, or medial line of the Milky Way may be considered as crossed by
that zone of large stars, which is marked out by the brilliant
constellation of _Orion_, the bright stars of Canis Major, and almost
all the more conspicuous stars of _Argo_, the Cross, the Centaur, Lupus,
and _Scorpion_. A great circle passing through ε Orionis and α Crucis
will mark out the axis of the zone in question, whose inclination to the
galactic circle is, therefore, about 20°, and whose appearance would
lead us to suspect that our nearest neighbours in the sidereal system
(if really such) form part of a subordinate sheet or stratum deviating
to that extent from parallelism to the general mass which, seen
projected on the heavens, forms the Milky Way.’”
These conclusions might seem probable enough when we compare the
supposed zone of bright stars with the very diagrammatic drawings of the
Milky Way as shown in many star maps; but when we consider the stars
referred to with reference to the more artistic and accurate
delineations of the Milky Way as drawn by Boeddicker, and even by Gould
himself, we see that most of them are involved in the milky light of the
Galaxy, and their connexion with the Milky Way itself seems quite as
probable as that they form a belt distinct from the galactic zone. The
apparent connexion of the stars in question with the Milky Way does not,
however, disprove the existence of Dr. Gould’s belt or zone of bright
stars. If the plane of the supposed belt nearly coincided with that of
the Milky Way, the apparent connexion might not be real.
Mr. J. R. Sutton advances the theory[149] that the Milky Way consists of
“a great ring of large stars”—Dr. Gould’s solar cluster above referred
to—“intersecting an equal ring of small ones (the Milky Way) at the
extremities of a common diameter.” He considers that “the great star
belt is a genuine girdle of stars in space, in which also the
foundations of the sidereal system are laid, the Milky Way being an
appendant to it of lesser rank.”
That the Milky Way really forms a ring of stars in space there is strong
evidence to show. Sir William Herschel’s original theory that the
galactic gleam is due to our sun being situated near the centre of an
indefinite stratum of stars—the “disc theory,” as it is termed—was
abandoned by its illustrious author in his later writings, and is now
considered to be wholly untenable by nearly all astronomers who have
studied the subject. Sir John Herschel remarks that the general aspect
of the galaxy near the Southern Cross indicates “that the Milky Way, in
this neighbourhood, at any rate, is really what it appears to be, a belt
or zone of stars separated from us by a starless interval.” It certainly
seems utterly improbable that the nearly circular blank space near the
Southern Cross, known as “the coal sack,” should represent a tunnel
through a disc, of which the thickness is comparatively small, while its
diameter, on the “disc theory,” stretches out almost to infinity. A
straight, tunnel-shaped opening of great length, pointing directly
towards the earth, would form an extraordinary phenomenon even in a
solitary instance; yet there are several somewhat similar openings to be
found in the Milky Way, as viewed both with the naked eye and with a
telescope. That _all_ these openings should represent tunnels radiating
from a common centre is quite beyond the bounds of probability, and,
indeed, such an hypothesis does not deserve serious consideration. With
reference to a photograph of the Milky Way in the constellation Cepheus,
Professor Barnard says, “the sky (or Milky Way) is broken up into
numerous black cracks or crevices. Looking at these peculiar features, I
cannot well see how one can avoid the conclusion that they are
necessarily real vacancies in the Milky Way, through which we look out
into the blackness of space.”[150] Using a telescope with a low power,
Mr. S. M. Baird Gemmill says, “December 1, 1886. In sweeping over the
constellation of Monoceros, I was much struck with the reticulated
character of the arrangement of the brighter stars upon the glimmering
background, and the way in which this background seemed to follow the
reticulation. By ‘brighter stars’ are meant stars of from 8 to 10
magnitude, for it was among these that I noticed this peculiarity of
arrangement. It put me in mind of M. M. Henry’s photographs of Cygnus.
The region seemed, in fact, a vast network of stars, the reticulations
of which were separated by desert, or comparatively desert spaces.”[151]
I have noticed the same thing myself while examining the Milky Way with
a binocular field-glass. On October 26, 1889, I noted as follows: “North
of Alpha Cygni, and near Xi and Nu Cygni, the nebulous light of the
Milky Way seems to cling round and follow streams of small stars in a
very remarkable way; numerous small ‘coal sacks’ and rifts are visible,
in which comparatively few stars are to be seen with the binocular.”
This observation has been fully confirmed by photographs of this region,
taken by Dr. Max Wolf in 1891.
[Illustration:
FIG. 19.—_Photograph of Milky Way, Sagittarius._
(From “Visible Universe.”)
]
That the Milky Way is not indefinitely extended in the line of sight
seems clearly shown by Sir John Herschel’s observations in the Southern
Hemisphere. In his “Outlines of Astronomy” (p. 578), he says: “When
examined with powerful telescopes, the constitution of this wonderful
zone is found to be no less various than its aspect to the eye is
irregular. In some regions, the stars of which it is wholly composed are
scattered with remarkable uniformity over immense tracts, while in
others the irregularity of their distribution is quite as striking,
exhibiting a rapid succession of closely clustering rich patches,
separated by comparatively poor intervals, and indeed, in some
instances, by spaces absolutely dark _and completely void of any
star_,[152] even of the smallest telescopic magnitude.... In some, for
instance, extremely minute stars, though never altogether wanting, occur
in numbers so moderate, as to lead us irresistibly to the conclusion
that, in those regions, we see _fairly through_ the starry stratum,
since it is impossible otherwise (supposing their light not
intercepted), that the members of the smaller magnitude should not go on
increasing _ad infinitum_. In such cases, moreover, the ground of the
heavens, as seen between the stars, is for the most part perfectly dark,
which again would not be the case if innumerable multitudes of stars,
too minute to be individually discernible, existed beyond. In other
regions we are presented with the phænomenon of an almost uniform degree
of brightness of the individual stars, accompanied with a very even
distribution of them over the ground of the heavens, both the larger and
smaller magnitudes being strikingly deficient. In such cases it is
equally impossible not to perceive that we are looking _through_ a sheet
of stars nearly of a size and of no great thickness compared with the
distance which separates them from us. Were it otherwise, we should be
driven to suppose the more distant stars uniformly the larger, so as to
compensate by their greater intrinsic brightness for their greater
distance, a supposition contrary to all probability. In others again,
and that not unfrequently, we are presented with a double phænomenon of
the same kind, _viz._, a tissue, as it were, of large stars spread over
another of very small ones, the intermediate magnitude being wanting.
The conclusion here seems equally evident that in such cases we look
through two sidereal sheets separated by a starless interval.”
An examination of the evidence at present available, with reference to
the distribution of the visible stars in space, has recently been
undertaken by Professor Kapteyn of Groningen, and an account of the
conclusions he has arrived at may prove of interest to the reader.
[Illustration:
FIG. 20.—_The Milky Way._
(From _Knowledge_, Nov., 1894.)
]
We must first explain that in order to obtain a clear view of the
construction of the visible universe, it would be necessary to know the
relative distances of a large number of stars; but as the distances of
only a few stars from the earth have yet been determined by actual
measurement, and the results hitherto obtained are open to much
uncertainty, we must have recourse to some other method of estimating
the distances. While travelling in a railway carriage, if we fix our
attention on trees, buildings, and other objects we pass on our journey,
it will be noticed that all objects apparently move past us in the
opposite direction to that in which we are travelling, and that the
nearer the object is the faster it seems to move with reference to
distant objects near the horizon. So it is with the stars. As we showed
in Chapter III., the sun is moving through space, carrying along with
the earth all the planets, satellites, and comets, forming the solar
system. The effect of this motion is to cause an apparent small motion
of the stars in the opposite direction, and the nearer the star is to
the earth, the greater will this apparent motion seem to be as in the
case of the railway train. In addition to this apparent motion, the
stars are themselves—like the sun—moving through space, and this _real_
motion is also visible. If this real motion takes place in the
_opposite_ direction to that in which the sun and earth are moving, it
will add to the apparent motion, and will increase the star’s “proper
motion,” as it is termed. If, on the other hand, the real motion is in
the _same_ direction as the earth’s motion, the proper motion will be
diminished. In either case, the nearer the star is to the earth, the
greater will be its apparent annual displacement on the background of
the heavens. The amount of the “proper motion” is, therefore, considered
by astronomers to form a reliable criterion of the star’s distance from
the earth, and the actual measures of distance which have been made show
that this assumption is approximately true. Of fourteen stars which have
proper motion of over three seconds of arc per annum, eleven have
yielded a measurable parallax, or displacement, due to the earth’s
annual motion round the sun; that is to say, eleven out of fourteen
fast-moving stars are within a measurable distance of the earth, and
are, therefore, near us, when compared with the great majority of stars
which are not within measurable distance, or, at least, are beyond the
reach of our present methods of measurement.
In the case of small groups of stars, we may assume that the real
motions of the individual stars take place indifferently in all
directions, and that consequently, taking an average of all the motions
of the stars composing the group, the effects due to the real motions
will destroy each other, and there will remain, as the most reliable
criterion, the effect due to the sun’s motion in space. If, however, we
compare the proper motions of groups situated in _different parts_ of
the sky, there is a consideration which, to a great extent, vitiates
this conclusion. For, near the point of the heavens, towards which the
sun and earth are moving, known as the “apex of the solar way,” and
probably situated not far from the bright star Vega, as indicated by
recent researches, and near the point away _from_ which the sun is
moving known as the _ant-apex_, about 15° south of Sirius, there will be
no apparent displacement due to the solar motion through space, as this
motion takes place in the line of sight with reference to these points
of the sky. The observed proper motion at these points will, therefore,
be solely due to the real motions of the stars themselves in those
regions. In other parts of the heavens, however, the total proper motion
will be a combination of the apparent and real motions of the stars, and
for stars in different parts of the sky, it will not follow that stars
having equal proper motions are necessarily at the same distance from
the earth. To make this point clearer, let us suppose that there are two
stars at absolutely the same distance from the earth, one situated at or
near the solar “apex,” and the other at a point 90° from the apex, and
let us suppose that both stars are moving through space with exactly the
same velocity and in the same direction, say at right angles to the
direction of the solar motion. Then in the case of the star near the
apex, the observed “proper motion” will be solely due to the star’s real
motion, and in the star 90° distant from the apex, the proper motion
will be solely due to the solar motion, as the star’s _real motion_,
being in the line of sight, will not be visible. Now, unless the stellar
motion and the solar motion happen to be equal, the observed “proper
motions” will not be equal, although both stars are at the same distance
from the earth. If both the stars are really at rest, the star at the
apex will have no proper motion, while the star 90° distant will have an
apparent proper motion due to the sun’s motion. To overcome this source
of error in estimating the distance of a star from its proper motion,
Professor Kapteyn made use of another measure, which is independent of
the solar motion. This is the component of the proper motion measured at
right angles to a great circle of the sphere passing through a star and
the solar apex. The amount of motion in this direction will evidently
not be affected by the sun’s motion, and from a discussion of the stars,
contained in the Draper “Catalogue of Stellar Spectra,” which were
observed by Bradley (and of which the proper motions are now known with
accuracy), Professor Kapteyn finds that this motion is “nearly inversely
proportional to the distance,” that is, the greater the motion, the less
the distance of the stars, and the smaller the motion, the greater the
distance. Excluding stars with proper motions greater than half a second
of arc per annum, Professor Kapteyn found that for stars at various
distances from the Milky Way this component of the “proper motion” forms
a good measure of distance.
As the result of his investigations on the subject, Professor Kapteyn
arrives at the following conclusions. Neglecting stars with small or
imperceptible proper motions, we have a group of stars which no longer
show any condensation in a plane. Stars with very small or no proper
motions show a condensation towards the plane of the Milky Way. This
applies to stars of the second or solar type, as well as to those of the
first or Sirian type of spectrum, and evidently indicates that the stars
composing the Milky Way lie at a great distance from the earth. The
extreme faintness of the majority of the stars composing the Galaxy
seems in favour of this conclusion. The condensation of stars of the
first type is more marked than those of the second, and this agrees with
the fact which has been noticed by Professor Pickering, that the
majority of the brighter stars of the Milky Way have spectra of the
Sirian type.
Professor Kapteyn finds that this condensation of stars with small
proper motions is very perceptible even for stars visible to the naked
eye, and is as well marked in those stars which have spectra of the
second type as for all the stars of the ninth magnitude; but for stars
of the first type the condensation is still more marked. He considers
that this condensation is either partly real, or that there is a real
thinning out of stars near the pole of the Milky Way. As already
mentioned (in the beginning of this chapter), Celoria’s observations
with a small telescope, compared with Sir William Herschel’s
observations with a large telescope, indicate clearly that there _is a
real thinning out_ of stars near the poles of the Galaxy.
Professor Kapteyn concludes that the arrangement of the stars suggested
by Struve—a modification of the “disc theory”—has no real
existence.[153] He attributes the fallacy in Struve’s hypothesis to the
fact that the mean distance of stars of a given magnitude in the Milky
Way, and outside it, is not the same.
Professor Kapteyn finds that the vicinity of the sun is almost
exclusively occupied by stars of the second or solar type, a conclusion
which evidently tends to strengthen Dr. Gould’s theory of a “solar
cluster.” He finds that the number of Sirian type stars increases
gradually with the distance, and that beyond a distance corresponding to
a proper motion of about ¹⁄₁₄th of a second of arc per annum, the Sirian
stars largely predominate. In the group of stars known as the Hyades,
however, the components of which have a common proper motion both in
amount and direction, stars of the first and second types appear to be
mixed, and Professor Kapteyn assumes that the two types represent
different phases of evolution, and that as the brightest stars of the
group are chiefly of the solar type, these stars must be the largest of
the group. From this fact he concludes the solar type stars are in a
less advanced stage of evolution than those of the Sirian type. This
does not agree with the generally accepted view. Professor Vogel
considers the Sirian stars to represent an earlier stage of stellar
evolution. Mr. Proctor held the same opinion, and in Professor Lockyer’s
hypothesis of increasing and decreasing temperatures in stars of various
types, he places the Sirian stars at the summit of the evolution curve,
and the sun and solar stars just below them on the descending branch of
the curve.[154] These hypotheses are in conformity also with the current
opinion that the sun is a cooling body. The discrepancy may perhaps be
explained by supposing that the _brighter_ stars of the Hyades form a
connected group, and that some, at least, of the fainter stars do not
belong to the group, but lie at a great distance behind it. In the case
of the Pleiades, which form a more evident cluster, I find from the
Draper “Catalogue of Stellar Spectra” that the great majority of the
brighter stars have spectra of the Sirian type. Most of the stars in the
Pleiades have a very similar proper motion, both in amount and in
direction, and there can be no doubt that most of the brighter stars, at
least, form a connected system. As already stated, it seems highly
probable that the fainter stars in the Pleiades lie far beyond the
brighter components, and have merely an optical connexion with them, and
the same may be the case in the Hyades. The superior brilliancy of the
stars composing the Hyades would suggest that they are nearer to the
earth than the Pleiades group, and they may possibly form members of
Gould’s “solar cluster.”
Assuming that the distances are inversely proportional to the proper
motions, Professor Kapteyn computes the relative volumes of the
spherical shells which contain the stars with different proper motions
(from one-tenth of a second to one second of arc and more). Comparing
these volumes with the corresponding number of stars, we arrive at an
estimate of the density of star distribution at various distances. The
result of this calculation shows that the distribution of stars of the
Sirian type approaches uniformity when a large number of the faint stars
(ninth magnitude) are considered. With reference to the stars of the
second type, however, the larger the proper motion the greater the
number of the stars; or, in other words, the second type, or solar
stars, are crowded together in the sun’s vicinity. Evidence in favour of
this conclusion is afforded by the fact that, of eight stars having the
largest measured parallax (and whose spectrum has been determined), I
find that seven have spectra of the solar type. The exception is Sirius,
which is evidently an exceptional star with reference to its brightness
and comparative proximity to the earth, no other star of the first
magnitude having nearly so large a parallax. Indeed, the average
distance of all the first magnitude stars is about forty times the
distance of Sirius.
Professor Kapteyn finds that the centre of greatest condensation of the
solar type stars lies near a point situated about ten degrees to the
west of the great nebula in Andromeda, and that this centre nearly
coincides with the point which, according to Struve and Herschel,
represents the apparent centre of the Milky Way considered as a ring.
This would indicate that the sun and solar system lie a little to the
north of the Milky Way, and towards a point situated in the northern
portion of the constellation of the Centaur. The fact is worth noting,
that the nearest fixed star to the earth, Alpha Centauri, lies not very
far from this point. Possibly there may be other stars in this direction
having a measured parallax, as the southern portion of the heavens has
not yet been thoroughly explored.
Professor Kapteyn finds that for stars of equal brightness, those of the
Sirian type are, on an average, about two and three-quarter times
farther from the earth than those of the solar type. Now, as light
varies inversely as the square of the distance, this would imply that
the Sirian stars are intrinsically brighter than those of the solar
type. This conclusion is confirmed by the great brilliancy of Sirius and
other stars of the same type in proportion to their mass. I have shown
in Chapter IV. that Sirius is about ten times brighter than the sun
would be if placed at the same distance, although its mass is only twice
the sun’s mass, as computed from the orbit of its satellite.
The general conclusions to be derived from the above results seems to be
that the sun is a member of a cluster of stars, possibly distributed in
the form of a ring, and that outside this ring, at a much greater
distance from us than the stars of the solar cluster, lies a
considerably richer ring-shaped cluster, the light of which, reduced to
nebulosity by immensity of distance, produces the Milky Way gleam of our
midnight skies.
INDEX
A
Aberration of light, discovered, 18;
a proof of the earth’s revolution, 57;
of meteor-radiants, 396
Aboul Wefa, the moon’s variation, 5
Acceleration, 152
Achromatic lens, 177
Adams, 449;
discovery of Neptune, 32, 349;
orbit of November meteors, 393
Aerolites. _See_ Meteorites
Airy, reduction of Greenwich observations, 19;
search for Neptune, 32
Albategnius, movement of the sun’s apogee, 5
Albedo of Mercury, 274;
of Venus, 278;
of the earth, 289;
of the moon, 290;
of Mars, 298, 334;
of asteroids, 312;
of Jupiter, 320;
of Jupiter’s satellites, 330, 332;
of Saturn, 334;
of rings, 338;
of Titan, 342;
of Uranus, 345;
of Neptune, 349
Alcor, 402
Alcyone, 499–502
Aldebaran, 403, 404, 407, 415, 421, 423, 427
Algol, 407, 415, 453, 457, 469–474
Almagest, 4, 6
Al-Mamûm’s school of astronomy at Baghdad, 5
Alphard, 409, 415
Alphonsine tables, 6
Al-Sûfi, description of the stars, 5;
Alphard, red, 415;
Algol, red, 472
Altair, 404, 427
Altazimuth, 184, 202
Altitude, 65
Amplitude, 66
Anderson, Dr., discovery of new star, 489
Andromeda nebula, 409, 529–532
Andromedæ, Gamma, 412, 417
— Nova, 489, 491
Andromede meteor-showers, 393, 394
Angelot, lunar volcanic action, 293
Annular eclipse, 113
— nebulæ, 526, 527
Antares, 404, 415
Anthelmus, new star, 484
Antlia, 468
Aphelion, 75
Apogee, 89
Apse Line, 75
Aquilæ, Eta, 467
Arago, nature of meteorites, 392;
parallax of 61 Cygni, 422
Arc of meridian, 130
Arcturus, 403, 405, 406, 415, 423, 427
Argelander, solar translation, 28;
survey of the heavens, 38;
comet of 1811, 357;
estimate of stars of ninth magnitude, 541
Argo Nebula, 522, 523, 549
— Eta, 462–464
Argon, not a solar element, 250;
peculiar qualities, 255;
found in meteorites, 389
Aries, first point of, 67
Aristarchus, heliocentric system, 4
Aristotle, description of a comet, 358
Asteroids, position in solar system, 229, 230, 310;
discoveries, 311, 314;
diameters, 312, 315;
computation of orbits, 314;
numbers and joint mass, 315;
distribution, 316;
groups, 317;
origin, 318
Asterope, 498, 499
Astronomy, Greek, 3, 4;
Arab, 4–6;
Tartar, 5;
of the Invisible, 31;
gravitational, 11, 33;
spectroscopic, 33–36;
photographic, 36–38
Astrophysics, foundation of, 36
Atmosphere, of the sun, 240, 271;
of Mercury, 277;
of Venus, 278, 279;
of the earth, 286, 313;
of the moon, 294, 313;
of Mars, 299, 307;
of Vesta, 312–313;
presence dependant upon mass, 313;
of Jupiter, 326;
of Uranus, 345
Atmospheric refraction, 52
Augmentation of moon’s diameter, 144
Aurigæ Beta, 404, 454, 456, 457
— New Star, 489
Auroræ, magnetic relations, 17, 288
Auwers’ reduction of Bradley’s observations, 19;
proper motion of Sirius, 437
Azimuth, 65
B
Babinet, rarity of cometary matter, 366
Baden-Powell, Sir George, eclipse-expedition, 259;
coronal photographs, 271
Bailey, Prof., 441, 464, 511, 513, 539
Ball, Sir Robert, 422, 433
Barnard, Prof., photograph of corona of January 1, 1889, 268–9;
effect of totality, 270;
zodiacal counterglow, 272;
photograph of eclipsed moon, 296;
drawing of Mars, 302;
seas of Mars, 306;
measurements of asteroids, 312;
markings on Jupiter’s satellites, 330;
discovery of fifth satellite, 331;
measures of Saturn, 335;
of ring-system, 330;
disappearance of rings, 337;
eclipse of Japetus, 338;
compression of Uranus, 343, 344;
Encke’s comet, 366;
comet-photographs, 378–381;
Swift’s comet, 383;
Nova in Auriga, 494;
Alcyone, 500;
curved nebulosity stretching over constellation of Orion, 520;
annular nebulæ, 526;
stars in streams, 551;
vacancies in the Milky Way, 554
Base line, 131
Baxendell, 484
Bayer, 404, 529
Behrmann, 400, 433, 541
Bellatrix, 408
Bélopolsky, spectrographic determination of Jupiter’s rotation, 325;
absolute velocity of 61 Cygni, 427;
spectroscopic examination of Castor, 451;
observation of Delta Cephei, 456;
Beta Lyræ, 466–467
Berberich, variability of Encke’s comet, 360
Berson, aeronautic ascent, 286
Bessel, _Fundamenta Astronomiæ_, 19;
astronomy of the invisible, 31, 32;
measurement of the Pleiades, 37;
Halley’s comet, 355;
comet of 1807, 362;
Epsilon Lyræ, 411
Betelgeuse, 404, 408, 415, 427
Bianchi, 459
Bianchini, rotation of Venus, 280
Biela, discovery of a comet, 365
Bigelow, theory of Zodiacal Light, 272
Binary stars, 431
Biot, meteoric fall, 387
Bird, quadrants, 19, 20
“Bird, Red,” 415
Birmingham, 417, 485, 486
“Blaze Star,” 485, 487
Bliss, astronomer-royal, 19
Bode’s law, 145, 232, 311, 317, 349
Boeddicker, Dr., heat-phases of eclipsed moon, 295
Bolometer, 226, 239
Bompas, 430
Bond, W. C., discoveries of Hyperion and of Saturn’s dusky ring, 25,
336, 341;
celestial photography, 36, 37;
the great nebula, 530
Bradley, discoveries of aberration and nutation, 18, 20;
reduction of his observations, 19;
Saturn’s rings, 337;
the distance of stars, 419–420;
Gamma Virginis, 445–446
Brahé, Tycho, the moon’s variation, 5;
career, 8;
scheme of the celestial movements, 9
Bredichin, theory of comets’ tails, 369, 370.
(_See also_ Tycho.)
Brenner, ashen light of Venus, 279;
rotation of Venus, 280
Brightest stars, 403, 404, 546
Brinkley, 422
British catalogue, 15, 16
Brooks’ cometary discoveries, 365, 371, 380
Bunsen, foundation of spectrum analysis, 33
Burnham, 433, 437, 441, 448, 509
C
Calcium, represented in Fraunhofer spectrum, 230;
in chromospheric and prominence-spectra, 258, 261, 262
Calendar, 86
Callandreau, capture of comets, 372
Campbell, Prof., spectrum of Mars, 306;
mountains on, 307
Canals of Mars, 301–305
Cancri, S., 474
— Zeta, 439, 440
Canis Majoris, R, 473
Canopus, 403
Capella, 403, 406, 415, 427
Capricornus, 411
Capture-theory of comets, 372
Carbon in sun, 242, 250;
in comets, 368;
in meteorites, 389
Cardinal points, 51
Carrington, sun-spot zones, 247;
sun’s rotation, 248, 249
Casey, 433
Cassegrain telescope, 180
Cassini, rotation of Venus, 280;
red spot on Jupiter, 323;
division of Saturn’s rings, 336;
discoveries of Saturnian satellites, 341
Cassiopeia, Chair of, 405, 481, 549
Cassiopeiæ, Eta, 413, 450
Castor, 404, 406, 413, 450, 451
Catalogues of stars, 70
Celoria, 433, 442, 540
Centauri, Alpha, 410, 413, 422, 440, 441
— Omega, 512, 513, 516, 539
— R, 478
Cephii Delta, 417, 456, 466
— U, 474
Ceraski, luminous night-clouds, 286;
discovery of U Cephei, 474
Ceres, discovery, 311;
diameter, 312
Cerulli, rotation of Venus, 280
Ceti, Mira, 458
Challis, search for Neptune, 32
Chandler, 462, 472, 476
Charlois, asteroidal discoveries, 314
Chemistry, universal, 35, 36;
solar, 250, 255;
of prominences, 256;
of chromosphere, 258;
of comets, 368, 370, 384;
of meteorites, 389
Chromosphere, 253, 258
Chronograph, 175
Chronometer, 175
Circle, meridian, 198;
transit, 198;
position, 208
Circumpolar stars, 46
Clairaut, verification of Newton’s law, 11;
calculation of Halley’s comet, 16
Clark, Alvan, great refractors, 26
— — G., detection of the companion of Sirius, 26, 437
Clarke, dimensions of earth, 134
Clausen, groups of comets, 361
Clerke, Agnes, appearance of R Sculptoris, 416;
examination of Pickering’s catalogue of stars, 541;
estimate of total light of stars to magnitude 9½, 543
Clock, astronomical, 174;
driving, 186;
sidereal, 68
Clock stars, 82
Clusters, globular, 507–517;
irregular, 497–507
“Coal sacks” in Milky Way, 554
Coelostat, 194
Collimation of transit instrument, 200
Collimator of spectroscope, 215
Colours of double stars, 417
Comæ Berenices, 434, 502, 549
Comet, Aristotle’s, 352, 353;
of 1743, 354;
Newton’s, 355;
of 1843, 358, 359;
Tebbutt’s, 362, 368;
Donati’s, 362, 369;
Lexell’s, 365, 370, 371;
Brooks’, of 1889, 365;
of 1893, 380;
Winnecke’s, 368, 371, 372;
Brorsen’s, 370;
Tuttle’s, 372, 393;
Wolf’s, 377;
Rordame’s, 383;
Gale’s, 383;
Leonid, 393, 395
— Halley’s, return in 1759, 16, 17;
status in solar system, 230, 232;
return in 1835, 335, 336;
type of tail, 369;
a client of Neptune, 371, 372
— Encke’s, disturbed by Mercury, 273;
rarefaction, 366;
acceleration, 307;
exempt from Jupiter’s influence, 371
— of 1811, structure, 356, 357;
type of tail, 369;
bulk, 383
— of 1843, surprising appearance, 358;
conditions of movement, 359
— of 1882, photographs, 38, 361;
transit, 359, 361;
period, 300;
spectrum, 369
Comet, Biela’s, discovery, 365;
duplication, 366;
related meteor-swarm, 393, 394
— Wells, spectrum, 368
— photographically detected, 377
Comets, orbits of, 108;
periodic, 109;
domiciled in solar system, 230, 371, 372;
granular nuclei, 353, 379, 384;
tenuity, 354, 384;
classification by Olbers, 358, 383;
groups, 359, 361, 362;
disruption, 360, 366, 379;
photographs, 361, 377, 380;
chemistry, 368, 370, 385;
luminous by electricity, 309, 384;
lost, 370;
short-period, 370, 371;
capture by planets, 371, 372, 384;
share sun’s translation, 372;
meteoric relationships, 384, 393, 394
— tails, multiple, 354, 355, 361, 377;
electrical theory, 357, 369, 383;
passage of the earth through, 302, 365;
three types, 369;
structure shown in photographs, 377, 383
Common, Dr., 25, 510, 520, 532, 534
Conjunctions, 99, 103
Constant of aberration, 59
Constellations, 45
Contacts in eclipse, 114
Copeland, Dr., cometary spectra, 368;
Nova in Auriga, 490;
helium, 519
Copernicus, residence in Italy, 7;
theory of planetary revolutions, 8, 9, 418
Cornelius, Gamma, 479
Corona Borealis, Eta, 437
— — Gamma, 442
— solar, 253;
compound nature of light, 202;
daylight photography, 267;
periodicity of type, 208, 270, 272;
photographs, 268–271;
rarefaction, 271, 361;
connexion with Zodiacal Light, 272, 273
Coronium, 238, 262
Co-tidal lines, 165
Coudé telescope, 27, 296
Crateris, R, 478
Craters, lunar, 292, 307
Crema meteorite, 386
Cross, Southern, 410, 416, 549
Crosswires, 195, 199, 206
Crucis, Kappa, 506
Cygni Beta, 417
— Chi, 460
— (_34_), 482
— (_61_), 422, 427
— Rho, new star near, 486
— Y, 474
Cygnus, 407
D
D’Alembert, verification of Newton’s Law, 11
D’Arrest, asteroidal orbits, 316;
comet, 371, 372
Darwin, G. H., tidal friction, 236;
origin of the moon, 236, 237;
density of Saturn, 333
Day and night, 52
— apparent solar, 79;
mean solar, 79
Declination, 66
De la Rue, celestial photography, 36, 295
Delphini, Beta, 435
— Gamma, 412
Deneb, 407
Denning, rotation of Saturn, 334;
discovery of a comet, 370;
August meteors, 391;
meteor-radiants, 395, 396
Density of earth, 160
Deslandres, prominence-photography, 261;
photographs of the sun as a bright-line star, 262;
daylight coronal photography, 267;
eclipse of 1893, 270;
rotation of Jupiter, 325
Dewar, atmospheric resistance to meteorites, 388
Dhurmsala meteorite, 389
Diameters, determination of, 141
Diamonds in meteorites, 390
Diffraction grating, 216
Direct movement, 89
— vision spectroscope, 216
Distance of the stars, 417
Doberck, Dr., 441, 442, 447, 450, 451
Dollond, invention of achromatic lenses, 21
Donati, discovery of a comet, 362;
cometary spectrum, 368
Double-slit method of photography, 261
Draconis, Gamma, 419, 420
Draper, Henry, photograph of the moon, 36
Dubjago, 435
Dunér, spectroscopic measurement of the sun’s rotation, 249;
R Hydræ, 462;
Y Cygni, 474;
Z Herculis, 475
E
Earth, shape of, 41, 134;
size of, 42, 134;
rotation of, 47, 48, 283, 284;
revolution of, 57;
orbit of, 59, 72;
varying speed of, 75;
real path of, 77;
shadow of, 110;
mass of, 159;
internal heat, 284, 285;
age, 285;
atmosphere, 286, 289;
magnetic relations, 287, 288
Easton, 532, 548
Eccentricity of ellipse, 74
Eclipse, solar, of 1842, 253;
of 1860, 254;
of 1868, 254;
of 1870, 258;
of 1896, 259, 271;
of 1882, 260, 268;
of 1878, 268;
of 1889, 268, 270;
of 1893, 270
Eclipses, lunar, 111;
partial, 111, 114;
annular, 113;
magnitude of, 113;
total of sun, 113;
duration of solar, 115;
number of in a year, 118;
recurrence of, 119;
of satellites, 121;
varieties of lunar, 295;
of Jupiter’s satellites, 329;
of Saturn’s, 342
Ecliptic, 56
— obliquity of, 61
Electrical theory of photospheric radiance, 242;
of corona, 271, 272;
of comets’ tails, 357, 358, 383;
of cometary luminosity, 369, 384
Electra, 498, 499
Elements of an orbit, 106
Elevating floor, 193
Elger, lunar _maria_, 290
Elkin, Dr., transit of great comet, 359;
meteorograph, 396;
measurements, 421–423, 425, 433, 438
Ellipse, properties of, 73;
eccentricity of, 74;
foci of, 74;
to draw an, 74
Elliptical nebulæ, 529–533
Elongations, 99
Encke, discovery of a comet, 366;
resisting medium, 367
Enoch, Book of, 404
Equation of time, 79
Equator, terrestrial, 50;
celestial, 66
Equatorial coudé, 193
Equatorial telescope, 185
Equinoxes, 55;
precession of, 69, 167, 170
Equulei, Delta, 433
Eridani, (_40_), 444
Espin, 460, 482, 494
Establishment of a port, 165
Ether of space, 546
Euler, lunar theory, 11
Evening star, 100
Evolution, of solar system, 235, 310;
of terrestrial, 236, 237, 283
Eye-pieces, 182
F
Fabricius, 458, 483
Fabry, cometary orbits, 372
Faculæ, associated with sun-spots, 244;
rotation, 249;
photographed, 262
Faye, planetary origin, 235, 350;
water on Mars, 299
Fényi, solar eruptions, 259, 260
Finder of telescope, 187
First Point of Aries, 67
Fixed stars, 45, 423
Flammarion, rotation of Venus, 280;
canals of Mars, 304;
condition of Mars, 309
Flamsteed, first astronomer-royal, 15;
stellar parallax, 18;
Flamsteed’s star, 461
Fleming, Mrs., 460, 465, 489, 494–496
Fletcher, 447
Fomalhaut, 404
Fontana, pseudo-satellite of Venus, 282
Forbes, ultra-Neptunian planets, 231
Foucault’s pendulum, 48–50
Fraunhofer, improvement of telescopes, 21;
solar spectrum mapped by, 34
Fraunhofer lines, 34, 249, 259, 271;
interpreted, 35, 250;
reflected in spectrum of Uranus, 346;
in spectra of comets, 368
Fritsche, 433
Frost, spectrograph of Uranus, 346
Froley, 434
G
Galaxy. _See_ Milky Way
Galileo, telescopic observations, 9;
double-star method of parallaxes, 28, 418
Gaseous nebula, 517
Gemini, star cluster in, 504
Geminorum, Zeta, 468
Gemma, Cornelius, 479
Gemmill, 554
Geocentric positions, 70
Geodesy, 129
Gill, Dr., photographs of comet of 1882, 38, 361;
parallax of Sirius, 421;
parallax and velocity, Lacaille, 424;
Omega Centauri, 513
Glasenapp, 433–434
Gledhill, red spot on Jupiter, 323
Globular clusters, 507
Gnomon, 125
Goodricke, 465, 466, 470
Gould, Dr., photographic measurement of the Pleiades, 37;
planetary photography, 327;
Pi Gruis and R Sculptoris, 416;
Kappa Crucis, 506;
stars in Southern Hemisphere, 541;
belt of stars intersecting the Milky Way, 551
Graduated circles, 171
Grating spectroscope, 216
Gravity, surface, on Mercury, 274;
on Venus, 278;
on the moon, 293;
on Mars, 298;
on Saturn, 335;
on Uranus, 345;
on Neptune, 349
Gravitation, laws of, 153;
universal, 156
Greenwich observations, 15, 19, 20
Groombridge, 424
Grosch, corona of 1867, 268
Grubb, Sir Howard, great refractors, 26
— Thomas, Melbourne reflecting telescope, 24
Guinand, optical glass, 21
Gully, Ludovic, 488
Gylden, 423
Gyroscope, 50
H
Hadley, improvement of reflecting telescopes, 21
Hale, spectrographs of prominences, 261;
calcium light pictures of sun and surroundings, 262;
double-slit method of coronal photography, 267
Hall, Prof. Asaph, discovery of the moons of Mars, 26, 309;
rotation of Saturn, 334
— Chester More, invention of achromatic lenses, 20
— Maxwell, 472
Halley, law of gravitation, 10;
acceleration of the moon, 12;
astronomer-royal, 16;
comet calculated by, 16;
transits of Venus, 17;
discovery of proper motion in stars, 423;
discovery of the star cluster in Hercules, 507
Harding, 548
Hartwig, 488
Harvest moon, 95
Heavens, diurnal motion of, 45
Heis, 400, 401, 541
Heliocentric positions, 70
Heliometer, 209
Helium, a chromospheric element, 255, 258;
extracted from clevite, 255
Helmholtz, maintenance of sun’s heat, 234;
past duration of sunlight, 285
Hencke, asteroidal discoveries, 314
Henderson, 422, 447
Henry’s belts of Uranus, 343
Hepidannus, 479
Herculis, Alpha, 413, 416
— Zeta, 435
— Z, 475
Herschel, Sir John, mathematical analysis at Cambridge, 15;
observations of nebulæ, 23, 31;
Magellanic clouds, 30, 31;
survey of the heavens, 31;
photography of sun-spots, 36;
telescope, 180;
great spot-group in 1837, 244;
cyclonic theory of sun-spots, 252;
Halley’s comet, 355;
comet of 1843, 358;
Biela’s comet, 365;
red stars, 416;
orbit of Gamma Virginis, 446;
Kappa Crucis, 506;
2 Messier, 511–512;
22 Messier, 514;
nebula round Eta Argus, 522–523;
30 Doradus, 524;
the trifid nebula, Sagittarius, 525;
planetary nebula, 528–529;
the Nubecula Major, 534–536;
Milky Way, crossed by zone of large stars, 552;
observations in the Southern Hemisphere, 554
— Sir William, the sun’s translation, 19, 28;
reflecting telescopes, 21–23;
discovery of Uranus, 21, 22;
of binary stars, 28;
comprehensive designs, 27, 29;
nebular theory, 30, 35;
rotation of Jupiter’s satellites, 331;
variability of Japetus, 341;
discovery of Uranian moons, 347;
binary stars, 419, 431;
motion real and apparent, 428;
Zeta Herculis, 435;
Xi Ursæ Majoris, 440;
70 Ophiuchi, 441;
5 Messier, 510
Hevelius, 459, 462, 484
Hind, 433, 474, 482, 484
Hipparchus, construction of a star catalogue, 3;
mathematical standpoint, 4
Holden, Prof., solar rotation, 249;
names of asteroids, 315;
helical nebulæ, 528
Holmes, discovery of a comet, 379
Holwarda, Phocylides, 458
Hooke, law of gravitation, 10;
observations of Greek letter Draconis, 18;
Gamma Arietis, 412;
parallax of Gamma Draconis, 419–420
Horizon, visible, 41;
sensible, 44;
celestial, 44;
rational, 44
Horrebow, satellite of Venus, 282
Hour circle, 186
Howlett, depression of sun-spot umbræ, 251
Huggins, Dr., stellar and nebular spectra, 35;
photographed, 37;
observations of prominences, 255;
daylight coronal photography, 267;
prismatic occultation of a star, 294;
spectrum of Mars, 306;
of Jupiter, 326;
of Uranus, 345;
of Winnecke’s comet, 368;
spectrograph of Tebbutt’s comet, 368;
measurement of motion in the line of sight, 426;
spectroscopic examination of new star, 493;
spectroscopic examination of the “fish-mouth” nebula, 518;
discovery of gaseous spectrum, 528
Humboldt, meteoric shower of 1799, 392;
temporary star of 1572, 479–481
Hussey, cometary forms, 380;
photograph of Rordame’s comet, 383
Huygens, 417, 517
Hyades, 407, 549
Hydræ, R, 462
Hydrogen, ultra-violet spectrum in stars, 37;
a gaseous metal, 250;
a constituent of prominences and chromosphere, 255, 258;
velocity of molecules, 313;
free in atmospheres of Uranus and Neptune, 346, 349;
assumed constituent of comets’ tails, 369, 370
Hypothesis of external galaxies, 546
I
Infinity of Space, 546
J
Jacob, 433, 447
Jacoby, measures of photographs, 37
Janssen, photograph of the sun, 243;
spectroscopic method of prominence-observation, 254;
double-slit method, 261
Japetus, remarkable eclipse, 338;
variability, 341;
plane of orbit, 342
Jesse, luminous night-clouds, 286
Job, Book of, 404
Johnson, 450
Juno, discovery, 311;
diameter and albedo, 312, 316;
a twin of Clotho, 317
Jupiter, long inequality, 12, 17;
disturbance of Halley’s comet, 16;
influence upon asteroidal distribution, 316–318;
mass and figure, 318;
rotation, 318, 325, 326;
density, 319, 326;
reflective power, 320;
belts and streamers, 321, 322, 326;
spots, 323, 325;
photographs, 327;
disturbance of comets, 371
Jupiter’s satellites, Galilean quartette, 9, 327, 328;
transits, 329;
constitution, 330;
fifth satellite, 331, 332
K
Kapteyn, 422, 556, 561–563
Keeler, drawings of Jupiter, 321;
description of markings, 322;
spectroscopic test of the meteoric constitution of Saturn’s rings,
339;
measuring velocities of nebula in line of sight, 428;
spectra of the Orion nebula, 519–520
Kelvin, Lord, subterranean temperature, 285
Kepler’s Laws, 10, 155, 339, 417
Kirch, 460, 470, 510
Kirchhoff, spectrum analysis, 33;
Fraunhofer’s lines, 34
Kirkwood, distribution of asteroids, 316, 317;
divisions in Saturn’s rings, 338
Kleiber, number of shooting stars, 390
Koch, 461
Kreutz, relations of great southern comets, 360
Krüger, 442
L
Lacaille, southern nebulæ, 30
Lagrange, verified principle of gravitation, 11;
stability of solar system, 13
Lajoye, 488
Lamp, fate of Brorsen’s comet, 370
Lane’s law, 242
Langley, solar radiation, 238, 239;
spectroscopic effects of sun’s rotation, 249;
temperature of the moon, 294;
fireball, 386
Laplace, verified Newton’s law, 11;
lunar acceleration, 12;
_Mécanique Céleste_, 13, 14;
nebular hypothesis, 235
Lassell, large reflectors, 24;
discoveries of Hyperion, Ariel, and Umbriel, 24, 341, 347;
Saturn’s dark ring, 336
Latitude, terrestrial, 50, 125;
celestial, 68;
of sun, 77;
geocentric, 135;
geographical, 135;
astronomical, 136;
variation of, 136
Leland, Miss, 511
Leonid meteors, 391–395
Leonis, Gamma, 413
— R, 461
Lepaute, Madame, computation of Halley’s comet, 16
Leverrier, discovery of Neptune, 32;
intra-Mercurian planet, 232;
mass of asteroids, 315;
orbit of November meteors, 395
Lewis, 426
Libræ, Delta, 473
Librations, of Mercury, 277;
of Venus, 281;
of the moon, 93, 289
Lick observatory, 25, 26
Light-equation, 329
“Light journey,” 420
Limited number of visible stars, 538, 545
Limiting apertures, 212
Lippershey, inventor of the telescope, 9
Lockyer, spectroscopic observations at the sun’s limb, 254;
classification of prominences, 250;
solar tornadoes, 259
Loewy, Coudé telescope, 27;
lunar photography, 296
Longitude, terrestrial, 50, 125;
celestial, 68
Lowell, rotation of Mercury, 277;
observations of Venus, 279, 281;
lakes of Mars, 301, 302;
relation to canals, 302–304
Luminous night-clouds, 286
Lunar distances, 129
— ecliptic limit, 112
Lyncis (_12_), 450
Lyra, annular nebula in, 526
Lyræ, Beta, 465
Lyraid meteors, 393, 395
M
Maclear, 464
Mädler, search for Martian moons, 309;
compression of Uranus, 343
Madrid meteorite, 385
Magellanic clouds, 30, 534–537
Magnetism, terrestrial, 287, 288
Magnitude, of eclipses, 113;
of stars, 212
Magnitudes, star, 403, 404
Mann, 433
Maps, 133
Maraldi, 462, 470, 511
Marchand, observations of the Zodiacal Light, 273
Markwick, Col., 547
Mars, phases of, 104;
parallax of, 147;
a superior planet, 297;
seasons, 298, 301, 302;
snow-caps, 299, 303, 306;
land and water, 299–301, 305, 306;
continents, 300, 301;
canals, 301, 304;
duplication, 301, 305;
spectrum, 306;
atmosphere, 307, 313;
mountains, 307;
climate, 308;
moons, 309, 310
Marth, Neptune’s satellite, 350
Mascari, rotation of Venus, 280
Maskelyne, astronomer-royal, 19;
founded _Nautical Almanac_, 20;
star-motions, 28
Mass, defined, 151;
sun, 156;
planets, 157;
moon, 158;
of asteroids, 158;
earth, 159;
satellites, 159
Maunder, 460, 488, 493
Maxwell, Clerk, constitution of Saturn’s rings, 337, 340
Mayer, Tobias, lunar tables, 11;
star-motions, 28
Mazapil meteorite, 396
Measurement, of earth, 42, 129;
of sun’s distance, 146;
of binary stars, 208;
of planets, 208
_Mécanique Céleste_, character, 13, 14
Megrez, 402
Mercury, Copernican theory of movements, 8;
transit of, 101;
phases of, 101;
orbit, 273, 274;
atmosphere, 274, 275;
rotation, 275–277;
as an abode of life, 277;
capture of Encke’s comet, 372
Meridian, 50;
line, 51;
arc of, 130;
circle, 198;
photometer, 214
Merope, 498, 499
Messier (_3_), 509
— (_5_), 510
— (_11_), 506
— (_22_), 514
— (_37_), 505
— (_51_), 533
— (_57_), 526
— (_80_), new star in, 485
— (_92_), 509
— (_99_), 534
— discoveries of nebulæ, 30
Metonic cycle, 92
Meteoric systems, 231, 390, 391;
radiants, 392, 395, 396
Meteorites, falls, 385–387;
legal status, 387;
velocities, 387, 388, 390;
thumb-marks, 388;
chemical composition, 389;
enclosed diamonds, 390
Meteors, Perseid, 391, 393;
Leonid, 391–393;
Andromede, 393–394, 396;
relations to comets, 393, 395
Micrometer, wire, or pillar, 205;
evolution of, 207
Michell, prevision of binary stars, 28
Midnight sun, 63
Milky Way, 402, 430, 555, 557
— — star streams, 9;
disc theory, 29
Minimum deviation, 215
Mira Ceti, 458, 459
Mitchell, 421, 431
Mizar, 402, 411, 455, 457
Molyneux, 419, 420
Montanari, 471
Month, 91
Moon, acceleration, 12;
_contumax sidus_, 16;
observations, 19;
apparent motion of, 87;
orbit of, 88, 94;
phases of, 89;
sidereal period of, 89;
synodic period of, 91;
rotation of, 92;
librations of, 93;
harvest, 95;
high and low, 97;
shadow of, 115;
distance of, 143;
size of, 144;
mass of, 158;
possible disintegration, 233;
origin, 236, 237;
rotation, 289;
cones and craters, 290, 292, 293;
rays and rills, 293;
absence of air and water, 294, 313;
temperature, 294, 295;
eclipses, 295;
photography, 295–297
Morning star, 100
Müller, surface of Mercury, 275;
photometry of asteroids, 312;
albedo of Jupiter, 320;
of Saturn, 334;
of Neptune, 349
Muscæ, R, 468
N
Nadir, 45
Nasir Eddin, planetary tables, 5
Nasmyth, conjunction of Mercury and Venus, 278
Nearest fixed stars, 417
Nebula, Orion, 23, 25, 30
Nebulæ, structure, 23;
spiral, 24;
photographs, 23, 25;
first discoveries, 29, 30;
status, 30, 31;
gaseous nature, 30, 35;
annular, 526, 527;
elliptical, 529, 533;
gaseous, 517–524;
planetary, 527–529;
spiral, 533, 534
Nebular hypothesis, 30, 35, 235, 530
Nebulous stars, 529
Neptune, discovery, 32, 229;
distance from the sun, 232;
dimensions, 349;
compression, 351;
retrograde rotation, 351;
planets as viewed from, 351, 352;
family of comets, 371, 372
Neptune’s satellite, discovery, 24;
plane of revolution, 350;
precessional disturbance, 351
Newall, 25-inch refractor, 26
Newcomb, Prof., past duration of sunlight, 285;
light changes of Ariel, 347;
satellite of Neptune, 351;
the runaway star, 424;
proper motion of Alcyone, 501
New stars, 477–497
Newton, H. A., capture of comets, 372;
meteoric cult, 387;
daily number of shooting stars, 390
— Sir Isaac, law of gravitation, 10, 11;
invention of reflecting telescope, 21;
comet of 1680, 355;
decay of comets, 366
Newtonian telescope, 179
Nichol, Dr., 508
Niesten, rotation of Venus, 280;
mass of asteroids, 315
Nodes, 94
North polar distance, 66
Nova Andromedæ, 488
— Aurigæ, 489
— Cassiopeiæ, 479
— Cygni, 486
— Ophiuchi, 484
— Serpentarii, 483
— Vulpeculæ, 484
Nubecula Major, 534
— Minor, 535
Number of visible stars, 538–544
Nutation, 169
O
Oases of Mars, 302–305
Object-glass, achromatic, 177;
photographic, 195;
photo-telescope, 196
Objective prism, 223
Obliquity of ecliptic, 61
Observatories, 191
— Lick, 189, 190, 202
— Nice, 192
— Yerkes, 189
Occultations, 121
— of stars, by the moon, 294;
by comets, 366
Olbers, discovery of Pallas and Vesta, 311;
origin of asteroids, 311, 316;
electrical theory of comets, 357;
classification, 358, 383;
comet discovered by, 371
Ophiuchi, Nova, 483–485
— (_70_), 441
— U, 473, 476
Opposition, 103, 105
Orbit, of earth, 72, 76;
of moon, 88;
elements of a planetary orbit, 106;
of binary stars, 432
Orion, 406, 408, 417
— great nebula in, 517–521
Orionis, Alpha (Betelgeuse), 404, 408, 415, 427
— Iota, 414
— Sigma, 414
— Theta, 414
“Owl,” nebula, 528