The Stars
Pliny says that Hipparchus "ventured to count the stars, a work arduous
even for the Deity." But this was quite a mistaken idea. Those visible to
the naked eye are comparatively few in number, and the enumeration of
those visible in an opera-glass--which of course far exceed those which
can be seen by unaided vision--is a matter of no great difficulty. Those
visible in a small telescope of 2-3/4 inches aperture have all been
observed and catalogued; and even those shown on photographs taken with
large telescopes can be easily counted. The present writer has made an
attempt in this direction, and taking an average of a large number of
counts in various parts of the sky, as shown on stellar photographs, he
finds a total of about 64 millions for the whole sky in both
hemispheres.[270] Probably the total number will not exceed 100 millions.
But this is a comparatively small number, even when compared with the
human population of our little globe.
With reference to the charts made by photography in the International
scheme commenced some years ago, it has now been estimated that the charts
will probably contain a total of about 9,854,000 stars down to about the
14th magnitude (13·7). The "catalogue plates" (taken with a shorter
exposure) will, it is expected, include about 2,676,500 stars down to
11-1/2 magnitude. These numbers may, however, be somewhat increased when
the work has been completed.[271] If this estimate proves to be correct,
the number of stars visible down to the 14th magnitude will be
considerably less than former estimates have made it.
Prof. E. C. Pickering estimates that the total number of stars visible on
photographs down to the 16th magnitude (about the faintest visible in the
great Lick telescope) will be about 50 millions.[272] In the present
writer's enumeration, above referred to, many stars fainter than the 16th
magnitude were included.
Admiral Smyth says, with reference to Sir William Herschel--perhaps the
greatest observer that ever lived--"As to Sir William himself, he could
unhesitatingly call every star down to the 6th magnitude, by its name,
letter, or number."[273] This shows great powers of observation, and a
wonderful memory.
On a photographic plate of the Pleiades taken with the Bruce telescope and
an exposure of 6 hours, Prof. Bailey of Harvard has counted "3972 stars
within an area 2° square, having Alcyone at its centre."[274] This would
give a total of about 41 millions for the whole sky, if of the same
richness.
With an exposure of 16 hours, Prof. H. C. Wilson finds on an area of less
that 110' square a total of 4621 stars. He thinks, "That all of these
stars belong to the Pleiades group is not at all probable. The great
majority of them probably lie at immense distances beyond the group, and
simply appear in it by projection."[274] He adds, "It has been found,
however, by very careful measurements made during the last 75 years at the
Königsbergh and Yale Observatories, that of the sixty-nine brighter stars,
including those down to the 9th magnitude, only eight show any certain
movement with reference to Alcyone. Since Alcyone has a proper motion or
drift of 6" per century, this means that all the brightest stars except
the eight mentioned are drifting with Alcyone and so form a true cluster,
at approximately the same distance from the earth. Six of the eight stars
which show relative drift are moving in the opposite direction to the
movement of Alcyone, and at nearly the same rate, so that their motion is
only apparent. They are really stationary, while Alcyone and the rest of
the cluster are moving past them."[275] This tends to show that the faint
stars are really _behind_ the cluster, and are unconnected with it.
It is a popular idea with some people that the Pole Star is the nearest of
all the stars to the celestial pole. But photographs show that there are
many faint stars nearer to the pole than the Pole Star. The Pole Star is
at present at a distance of 1° 13' from the real pole of the heavens, but
it is slowly approaching it. The minimum distance will be reached in the
year 2104. From photographs taken by M. Flammarion at the Juvisy
Observatory, he finds that there are at least 128 stars nearer to the pole
than the Pole Star! The nearest star to the pole was, in the year 1902, a
small star of about 12-1/2 magnitude, which was distant about 4 minutes of
arc from the pole.[276] The estimated magnitude shows that the Pole Star
is nearly 10,000 times brighter than this faint star!
It has been found that Sirius is bright enough to cast a shadow under
favourable conditions. On March 22, 1903, the distinguished French
astronomer Touchet succeeded in photographing the shadow of a brooch cast
by this brilliant star. The exposure was 1{h} 5{m}.
Martinus Hortensius seems to have been the first to see stars in daylight,
perhaps early in the seventeenth century. He mentions the fact in a letter
to Gassendi dated October 12, 1636, but does not give the date of his
observation. Schickard saw Arcturus in broad daylight early in 1632. Morin
saw the same bright star half an hour after sunset in March, 1635.
Some interesting observations were made by Professors Payne and H. C.
Wilson, in the summer of 1904, at Midvale, Montana (U.S.A.), at a height
of 4790 feet above sea-level. At this height they found the air very clear
and transparent. "Many more stars were visible at a glance, and the
familiar stars appeared more brilliant.... In the great bright cloud of
the Milky Way, between [Greek: b] and [Greek: g] Cygni, one could count
easily sixteen or seventeen stars, besides the bright ones [Greek: ê] and
[Greek: ch],[277] while at Northfield it is difficult to distinctly see
eight or nine with the naked eye." Some nebulæ and star fields were
photographed with good results by the aid of a 2-1/2-inch Darlot lens and
3 hours' exposure.[278]
Prof. Barnard has taken some good stellar photographs with a lens of only
1-1/2 inches in diameter, and 4 or 5 inches focus belonging to an
ordinary "magic lantern"! He says that these "photographs with the small
lens show us in the most striking manner how the most valuable and
important information may be obtained with the simplest means."[279]
With reference to the rising and setting of the stars due to the earth's
rotation on its axis, the late Sir George B. Airy, Astronomer Royal of
England, once said to a schoolmaster, "I should like to know how far your
pupils go into the first practical points for which reading is scarcely
necessary. Do they know that the stars rise and set? Very few people in
England know it. I once had a correspondence with a literary man of the
highest rank on a point of Greek astronomy, and found that he did not know
it!"[280]
Admiral Smyth says, "I have been struck with the beautiful blue tint of
the smallest stars visible in my telescope. This, however, may be
attributed to some optical peculiarity." This bluish colour of small stars
agrees with the conclusion arrived at by Prof. Pickering in recent years,
that the majority of faint stars in the Milky Way have spectra of the
Sirian type and, like that brilliant star, are of a bluish white colour.
Sir William Herschel saw many stars of a redder tinge than other observers
have noticed. Admiral Smyth says, "This may be owing to the effect of his
metallic mirror or to some peculiarity of vision, or perhaps both."[281]
The ancient astronomers do not mention any coloured stars except white and
red. Among the latter they only speak of Arcturus, Aldebaran, Pollux,
Antares, and Betelgeuse as of a striking red colour. To these Al-Sufi adds
Alphard ([Greek: a] Hydræ).
Sir William Herschel remarked that no decidedly green or blue star "has
ever been noticed unassociated with a companion brighter than itself." An
exception to Herschel's rule seems to be found in the case of the star
[Greek: b] Libræ, which Admiral Smyth called "pale emerald." Mr. George
Knott observed it on May 19, 1852, as "beautiful pale green" (3·7 inches
achromatic, power 80), and on May 9, 1872, as "fine pale green" (5·5
inches achromatic, power 65).
The motion of stars in the line of sight, as shown by the
spectroscope--should theoretically alter their brightness in the course of
time; those approaching the earth becoming gradually brighter, while those
receding should become fainter. But the distance of the stars is so
enormous that even with very high velocities the change would not become
perceptible for ages. Prof. Oudemans found that to change the brightness
of a star by only one-tenth of a magnitude--a quantity barely perceptible
to the eye-a number of years would be necessary, which is represented by
the formula
5916 years
-----------------
parallax × motion
for a star approaching the earth, and for a receding star
6195 years
----------
p × m
This is in geographical miles, 1 geographical mile being equal to 4·61
English miles.
Reducing the above to English miles, and taking an average for both
approaching and receding stars, we have
27,660 years
------------
p × m
where p = parallax in seconds of arc, and m = radial velocity in English
miles per second.
Prof. Oudemans found that the only star which could have changed in
brightness by one-tenth of a magnitude since the time of Hipparchus is
Aldebaran. This is taking its parallax as 0"·52. But assuming the more
reliable parallax 0"·12 found by Dr. Elkin, this period is 4-1/3 times
longer. For Procyon, the period would be 5500 years.[282] The above
calculation shows how absurd it is to suppose that any star could have
gained or lost in brightness by motion in the line of sight during
historical times. The "secular variation" of stars is quite another
thing. This is due to physical changes in the stars themselves.
The famous astronomer Halley, the second Astronomer Royal at Greenwich,
says (_Phil. Trans._, 1796), "Supposing the number of 1st magnitude stars
to be 13, at twice the distance from the sun there may be placed four
times as many, or 52; which with the same allowance would nearly represent
the star we find to be of the 2nd magnitude. So 9 × 13, or 117, for those
at three times the distance; and at ten times the distance 100 × 13, or
1300 stars; of which distance may probably diminish the light of any of
the stars of the 1st magnitude to that of the 6th, it being but the
hundredth part of what, at their present distance, they appear with." This
agrees with the now generally accepted "light ratio" of 2·512 for each
magnitude, which makes a first magnitude star 100 times the light of a 6th
magnitude.
On the 4th of March, 1796,[283] the famous French astronomer Lalande
observed on the meridian a star of small 6th magnitude, the exact position
of which he determined. On the 15th of the same month he again observed
the star, and the places found for 1800 refer to numbers 16292-3 of the
reduced catalogue. In the observation of March 4 he attached the curious
remark, "Étoile singulière" (the observation of March 15 is without
note). This remark of Lalande has puzzled observers who failed to find any
peculiarity about the star. Indeed, "the remark is a strange one for the
observer of so many thousands of stars to attach unless there was really
something singular in the star's aspect at the time." On the evening of
April 18, 1887, the star was examined by the present writer, and the
following is the record in his observing book, "Lalande's étoile
singulière (16292-3) about half a magnitude less than [Greek: ê] Cancri.
With the binocular I see two streams of small stars branching out from it,
north preceding like the tails of comet." This may perhaps have something
to do with Lalande's curious remark.
The star numbered 1647 in Baily's _Flamsteed Catalogue_ is now known to
have been an observation of the planet Uranus.[284]
Prof. Pickering states that the fainter stars photographed with the 8-inch
telescope at Cambridge (U.S.A.) are invisible to the eye in the 15-inch
telescope.[285]
Sir Norman Lockyer finds that the lines of sulphur are present in the
spectrum of the bright star Rigel ([Greek: b] Orionis).[286]
About 8-1/2° south of the bright star Regulus ([Greek: a] Leonis) is a
faint nebula (H I, 4 Sextantis). On or near this spot the Capuchin monk De
Rheita fancied he saw, in the year 1643, a group of stars representing
the napkin of S. Veronica--"sudarium Veronicæ sive faciem Domini maxima
similitudina in astris expressum." And he gave a picture of the napkin and
star group. But all subsequent observers have failed to find any trace of
the star group referred to by De Rheita![287]
The Bible story of the star of the Magi is also told in connection with
the birth of the sun-gods Osiris, Horus, Mithra, Serapis, etc.[288] The
present writer has also heard it suggested that the phenomenon may have
been an apparition of Halley's comet! But as this famous comet is known to
have appeared in the year B.C. 11, and as the date of the Nativity was
probably not earlier than B.C. 5, the hypothesis seems for this (and other
reasons) to be inadmissible. It has also been suggested that the
phenomenon might have been an appearance of Tycho Brahé's temporary star
of 1572, known as the "Pilgrim star"; but there seems to be no real
foundation for such an hypothesis. There is no reason to think that
"temporary" or new stars ever appear a second time.
Admiral Smyth has well said, "It checks one's pride to recollect that if
our sun with the whole system of planets, asteroids, and moons, and comets
were to be removed from the spectator to the distance of the nearest
fixed star, not one of them would be visible, except the sun, which would
then appear but as a star of perhaps the 2nd magnitude. Nay, more, were
the whole system of which our globe forms an insignificant member, with
its central luminary, suddenly annihilated, no effect would be produced on
those unconnected and remote bodies; and the only annunciation of such a
catastrophe in the Sidereal "Times" would be that a small star once seen
in a distant quarter of the sky had ceased to shine."[289]
Prof. George C. Comstock finds that the average parallax of 67 selected
stars ranging in brightness between the 9th and the 12th magnitude, is of
the value of 0"·0051.[290] This gives a distance representing a journey
for light of about 639 years!
Mr. Henry Norris Russell thinks that nearly all the bright stars in the
constellation of Orion are practically at the same distance from the
earth. His reasons for this opinion are: (1) the stars are similar in
their spectra and proper motions, (2) their proper motions are small,
which suggests a small parallax, and therefore a great distance from the
earth. Mr. Russell thinks that the average parallax of these stars may
perhaps be 0"·005, which gives a distance of about 650 "light
years."[291]
According to Sir Norman Lockyer's classification of the stars, the order
of _increasing_ temperature is represented by the following, beginning
with those in the earliest stage of stellar evolution:--Nebulæ, Antares,
Aldebaran, Polaris, [Greek: a] Cygni, Rigel, [Greek: e] Tauri, [Greek: b]
Crucis. Then we have the hottest stars represented by [Greek: e] Puppis,
[Greek: g] Argus, and Alnitam ([Greek: e] Orionis). _Decreasing_
temperature is represented by (in order), Achernar, Algol, Markab, Sirius,
Procyon, Arcturus, 19 Piscium, and the "Dark Stars."[292] But other
astronomers do not agree with this classification. Antares and Aldebaran
are by some authorities considered to be _cooling_ suns.
According to Ritter's views of the Constitution of the Celestial Bodies,
if we "divide the stars into three classes according to age corresponding
to these three stages of development, we shall assign to the first class,
A, those stars still in the nebular phase of development; to the second
class, B, those in the transient stage of greatest brilliancy; and to the
class C, those stars which have already entered into the long period of
slow extinction. It should be noted in this classification that we refer
to relative and not absolute age, since a star of slight mass passes
through the successive phases of its development more rapidly than the
star of greater mass."[293] Ritter comes to the conclusion that "the
duration of the period in which the sun as a star had a greater brightness
than at present was very short in comparison with the period in which it
had and will continue to have a brightness differing only slightly from
its present value."[294]
In a valuable and interesting paper on "The Evolution of Solar
Stars,"[295] Prof. Schuster says that "measurements by E. F. Nichols on
the heat of Vega and Arcturus indicated a lower temperature for Arcturus,
and confirms the conclusion arrived at on other grounds, that the hydrogen
stars have a higher temperature than the solar stars." "An inspection of
the ultraviolet region of the spectrum gives the same result. These
different lines of argument, all leading to the same result, justify us in
saying that the surface temperature of the hydrogen stars is higher than
that of the solar stars. An extension of the same reasoning leads to the
belief that the helium stars have a temperature which is higher still."
Hence we have Schuster, Hale, and Sir William Huggins in agreement that
the Sirian stars are hotter than the solar stars; and personally I agree
with these high authorities. The late Dr. W. E. Wilson, however, held the
opinion that the sun is hotter that Sirius!
Schuster thinks that Lane's law does not apply to the temperature of the
photosphere and the absorbing layers of the sun and stars, but only to the
portions between the photosphere and the centre, which probably act like a
perfect gas. On this view he says the interior might become "hotter and
hotter until the condensation had reached a point at which the laws of
gaseous condensation no longer hold."
With reference to the stars having spectra of the 3rd and 4th type
(usually orange and red in colour), Schuster says--
"The remaining types of spectra belong to lower temperature still, as
in place of metallic lines, or in addition to them, certain bands
appear which experiments show us invariably belong to lower
temperature than the lines of the same element.
"If an evolutionary process has been going on, which is similar for
all stars, there is little doubt that from the bright-line stars down
to the solar stars the order has been (1) helium or _Orion_ stars, (2)
hydrogen or Sirian stars, (3) calcium or Procyon stars, (4) solar or
Capellan stars."
My investigations on "The Secular Variation of Starlight" (_Studies in
Astronomy_, chap. 17, and _Astronomical Essays_, chap. 12) based on a
comparison of Al-Sufi's star magnitudes (tenth century) with modern
estimates and measures, tend strongly to confirm the above views.
With regard to the 3rd-type stars, such as Betelgeuse and Mira Ceti,
Schuster says, "It has been already mentioned that observers differ as to
whether their position is anterior to the hydrogen or posterior to the
solar stars, and there are valid arguments on both sides."
Scheiner, however, shows, from the behaviour of the lines of magnesium,
that stars of type I. (Sirian) are the hottest, and type III. the coolest,
and he says, we have "for the first time a direct proof of the correctness
of the physical interpretation of Vogel's spectral classes, according to
which class II. is developed by cooling from I., and III. by a further
process of cooling from II."[296]
Prof. Hale says that "the resemblance between the spectra of sun-spots and
of 3rd-type stars is so close as to indicate that the same cause is
controlling the relative intensities of many lines in both instances. This
cause, as the laboratory work indicates, is to be regarded as reduced
temperature."[297]
According to Prof. Schuster, "a spectrum of bright lines may be given by a
mass of luminous gas, even if the gas is of great thickness. There is,
therefore, no difficulty in explaining the existence of stars giving
bright lines." He thinks that the difference between "bright line" stars
and those showing dark lines depends upon the rate of increase of the
temperature from the surface towards the centre. If this rate is slow,
bright lines will be seen. If the rate of increase is rapid, the
dark-line spectrum shown by the majority of the stars will appear. This
rate, he thinks, is regulated by the gravitational force. So that in the
early stages of condensation bright lines are more likely to occur. "If
the light is not fully absorbed," both bright and dark lines of the same
element may be visible in the same star. Schuster considers it quite
possible that if we could remove the outer layers of the Sun's atmosphere,
we should obtain a spectrum of bright lines.[298]
M. Stratonoff finds that stars having spectra of the Orion and Sirian
types--supposed to represent an early stage in stellar evolution--tend to
congregate in or near the Milky Way. Star clusters in general show a
similar tendency, "but to this law the globular clusters form an
exception."[299] We may add that the spiral nebulæ--which seem to be
scattered indifferently over all parts of the sky--also seem to form an
exception; for the spectra of these wonderful objects seem to show that
they are really star clusters, in which the components are probably
relatively small; that is, small in comparison with our sun.
If we accept the hypothesis that suns and systems were evolved from
nebulæ, and if we consider the comparatively small number of nebulæ
hitherto discovered in the largest telescopes--about half a million; and
if we further consider the very small number of red stars, or those having
spectra of the third and fourth types--usually considered to be dying-out
suns--we seem led to the conclusion that our sidereal system is now at
about the zenith of its life-history; comparatively few nebulæ being left
to consolidate into stars, and comparatively few stars having gone far on
the road to the final extinction of their light.
Prof. Boss of Albany (U.S.A.) finds that about forty stars of magnitudes
from 3-1/2 to 7 in the constellation Taurus are apparently drifting
together towards one point. These stars are included between about R.A.
3{h} 47{m} to 5{h} 4{m}, and Declination + 5° to + 23° (that is, in the
region surrounding the Hyades). These motions apparently converge to a
point near R.A. 6{h}, Declination + 7° (near Betelgeuse). Prof. Boss has
computed the velocity of the stars in this group to be 45·6 kilometres
(about 28 miles) a second towards the "vanishing point," and he estimated
the average parallax of the group to be 0"·025--about 130 years' journey
for light. Although the motions are apparently converging to a point, it
does not follow that the stars in question will, in the course of ages,
meet at the "vanishing point." On the contrary, the observed motions show
that the stars are moving in parallel lines through space. About 15
kilometres of the observed speed is due to the sun's motion through space
in the opposite direction. Prof. Campbell finds from spectroscopic
measures that of these forty stars, nine are receding from the earth with
velocities varying from 12 to 60 kilometres a second, and twenty-three
others with less velocities than 38 kilometres.[300] It will be obvious
that, as there is a "vanishing point," the motion in the line of sight
must be one of _recession_ from the earth.
It has been found that on an average the parallax of a star is about
one-seventh of its "proper motion."[301]
Adopting Prof. Newcomb's parallax of 0"·14 for the famous star 1830
Groombridge, the velocity perpendicular to the line of sight is about 150
miles a second. The velocity _in_ the line of sight--as shown by the
spectroscope--is 59 miles a second approaching the earth. Compounding
these two velocities we find a velocity through space of about 161 miles a
second!
An eminent American writer puts into the mouth of one of his characters, a
young astronomer, the following:--
"I read the page
Where every letter is a glittering sun."
From an examination of the heat radiated by some bright stars, made by
Dr. E. F. Nicholls in America with a very sensitive radiometer of his own
construction, he finds that "we do not receive from Arcturus more heat
than we should from a candle at a distance of 5 or 6 miles."
With reference to the progressive motion of light, and the different times
taken by light to reach the earth from different stars, Humboldt says,
"The aspect of the starry heavens presents to us objects of _unequal
date_. Much has long ceased to exist before the knowledge of its presence
reaches us; much has been otherwise arranged."[302]
The photographic method of charting the stars, although a great
improvement on the old system, seems to have its disadvantages. One of
these is that the star images are liable to disappear from the plates in
the course of time. The reduction of stellar photograph plates should,
therefore, be carried out as soon as possible after they are taken. The
late Dr. Roberts found that on a plate originally containing 364 stars, no
less than 130 had completely disappeared in 9-1/4 years!
It has been assumed by some writers on astronomy that the faint stars
visible on photographs of the Pleiades are at practically the same
distance from the earth as the brighter stars of the cluster, and that
consequently there must be an enormous difference in actual size between
the brighter and fainter stars. But there is really no warrant for any
such assumption. Photographs of the vicinity show that the sky all round
the Pleiades is equally rich in faint stars. It seems, therefore, more
reasonable to suppose that most of the faint stars visible in the Pleiades
are really far behind the cluster in space. For if _all_ the faint stars
visible on photographs belonged to the cluster, then if we imagine the
cluster removed, a "hole" would be left in the sky, which is of course
utterly improbable, and indeed absurd. An examination of the proper
motions tends to confirm this view of the matter, and indicates that the
Pleiades cluster is a comparatively small one and simply projected on a
background of fainter stars.
It has long been suspected that the famous star 61 Cygni, which is a
double star, forms a binary system--that is, that the two stars composing
it revolve round their common centre of gravity and move together through
space. But measures of parallax made by Herman S. Davis and Wilsing seem
to show a difference of parallax between the two components of about 0·08
of a second of arc. This difference of parallax implies a distance of
about 2-1/4 "light years" between the two stars, and "if this is correct,
the stars are too remote to form a binary system. The proper motions of
5"·21 and 5"·15 seem to show that they are moving in nearly parallel
directions; but are probably slowly separating." Mr. Lewis, however,
thinks that a physical connection probably exists.[303]
Dante speaks of the four bright stars of the Southern Cross as
emblematical of the four cardinal virtues, Justice, Temperance, Fortitude,
and Prudence; and he seems to refer to the stars Canopus, Achernar, and
Foomalhaut under the symbols of Faith, Hope, and Charity. The so-called
"False Cross" is said to be formed by the stars [Greek: k], [Greek: d],
[Greek: e], and [Greek: i] of the constellation Argo Navis. But it seems
to me that a better (although larger) cross is formed by the stars [Greek:
a] Centauri and [Greek: a], [Greek: b], and [Greek: g] of Triangulum
Australis.
Mr. Monck has pointed out that the names of the brightest stars seem to be
arranged alphabetically in order of colour, beginning with red and ending
with blue. Thus we have Aldebaran, Arcturus, Betelgeuse, Capella, Procyon,
Regulus, Rigel, Sirius, Spica and Vega. But as the origin of these names
is different, this must be merely a curious coincidence.[304] And, to my
eye at least, Betelgeuse is redder than Arcturus.
The poet Longfellow speaks of the--
"Stars, the thoughts of God in the heavens,"[305]
and Drayton says--
"The stars to me an everlasting book
In that eternal register, the sky."[306]
Observing at a height of 12,540 feet on the Andes, the late Dr. Copeland
saw Sirius with the naked eye less than 10 minutes before sunset.[307] He
also saw Jupiter 3{m} 47{s} before sunset; and the following bright
stars--Canopus, 0{m} 52{s} before sunset; Rigel ([Greek: b] Orionis) 16{m}
32{s} after sunset; and Procyon 11{m} 28{s} after sunset. From a height of
12,050 feet at La Paz, Bolivia, he saw with the naked eye in February,
1883, ten stars in the Pleiades in full moonlight, and seventeen stars in
the Hyades. He also saw [Greek: s] Tauri double.[308]
Humboldt says, "In whatever point the vault of heaven has been pierced by
powerful and far-penetrating telescopic instruments, stars or luminous
nebulæ are everywhere discoverable, the former in some cases not exceeding
the 20th or 24th degree of telescopic magnitude."[309] But this is a
mistake. No star of even the 20th magnitude has ever been seen by any
telescope. Even on the best photographic plates it is doubtful that any
stars much below the 18th magnitude are visible. To show a star of the
20th magnitude--if such stars exist--would require a telescope of 144
inches or 12 feet in aperture. To show a star of the 24th magnitude--if
such there be--an aperture of 33 feet would be necessary![310]
It is a popular idea that stars may be seen in the daytime from the bottom
of a deep pit or high chimney. But this has often been denied. Humboldt
says, "While practically engaged in mining operations, I was in the habit,
during many years, of passing a great portion of the day in mines where I
could see the sky through deep shafts, yet I never was able to observe a
star."[311]
Stars may, however, be seen in the daytime with even small telescopes. It
is said that a telescope of 1 inch aperture will show stars of the 2nd
magnitude; 2 inches, stars of the 3rd magnitude; and 4 inches, stars of
the 4th magnitude. But I cannot confirm this from personal observation. It
may be so, but I have not tried the experiment.
Sir George Darwin says--
"Human life is too short to permit us to watch the leisurely procedure
of cosmical evolution, but the celestial museum contains so many
exhibits that it may become possible, by the aid of theory, to piece
together, bit by bit, the processes through which stars pass in the
course of their evolutions."[312]
The so-called "telluric lines" seen in the solar spectrum, are due to
water vapour in the earth's atmosphere. As the light of the stars also
passes through the atmosphere, it is evident that these lines should also
be visible in the spectra of the stars. This is found to be the case by
Prof. Campbell, Director of the Lick Observatory, who has observed all the
principal bands in the spectrum of every star he has examined.[313]
The largest "proper motion" now known is that of a star of the 8-1/2
magnitude in the southern hemisphere, known as Cordoba Zone V. No. 243.
Its proper motion is 8·07 seconds of arc per annum, thus exceeding that of
the famous "runaway star," 1830 Groombridge, which has a proper motion of
7·05 seconds per annum. This greater motion is, however, only apparent.
Measures of parallax show that the southern "runaway" is much nearer to us
than its northern rival, its parallax being 0"·32, while that of
Groombridge 1830 is only 0"·14. With these data the actual velocity across
the line of sight can be easily computed. That of the southern star comes
out 80 miles a second, while that of Groombridge 1830 is 148 miles a
second. The actual velocity of Arcturus is probably still greater.
The poet Barton has well said--
"The stars! the stars! go forth at night,
Lift up thine eyes on high,
And view the countless orbs of light,
Which gem the midnight sky.
Go forth in silence and alone,
This glorious sight to scan,
And bid the humbled spirit own
The littleness of man."