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ASTRONOMICAL CURIOSITIES
FACTS AND FALLACIES
ASTRONOMICAL CURIOSITIES
FACTS AND FALLACIES
BY J. ELLARD GORE
MEMBER OF THE ROYAL IRISH ACADEMY FELLOW OF THE
ROYAL ASTRONOMICAL SOCIETY CORRESPONDING MEMBER
OF THE ROYAL ASTRONOMICAL SOCIETY OF CANADA ETC.
AUTHOR OF "ASTRONOMICAL ESSAYS," "STUDIES IN
ASTRONOMY," "THE VISIBLE UNIVERSE," ETC.
LONDON
CHATTO & WINDUS
1909
PRINTED BY
WILLIAM CLOWES AND SONS, LIMITED
LONDON AND BECCLES
_All rights reserved_
PREFACE
The curious facts, fallacies, and paradoxes contained in the following
pages have been collected from various sources. Most of the information
given will not, I think, be found in popular works on astronomy, and will,
it is hoped, prove of interest to the general reader.
J. E. G.
_September, 1909._
CONTENTS
PAGE
CHAPTER
I. THE SUN 1
II. MERCURY 10
III. VENUS 17
IV. THE EARTH 32
V. THE MOON 48
VI. MARS 59
VII. THE MINOR PLANETS 68
VIII. JUPITER 74
IX. SATURN 84
X. URANUS AND NEPTUNE 91
XI. COMETS 97
XII. METEORS 117
XIII. THE ZODIACAL LIGHT AND GEGENSCHEIN 127
XIV. THE STARS 135
XV. DOUBLE AND BINARY STARS 160
XVI. VARIABLE STARS 170
XVII. NEBULÆ AND CLUSTERS 191
XVIII. HISTORICAL 217
XIX. THE CONSTELLATIONS 239
XX. THE VISIBLE UNIVERSE 313
XXI. GENERAL 329
INDEX 359
ILLUSTRATIONS
PAGE
AL-SUFI'S "EARTHEN JAR" 247
AL-SUFI'S "FISHES" IN ANDROMEDA 249
ASTRONOMICAL CURIOSITIES
CHAPTER I
The Sun
Some observations recently made by Prof. W. H. Pickering in Jamaica, make
the value of sunlight 540,000 times that of moonlight. This makes the
sun's "stellar magnitude" minus 26·83, and that of moonlight minus 12·5.
Prof. Pickering finds that the light of the full moon is equal to 100,000
stars of zero magnitude. He finds that the moon's "albedo" is about
0·0909; or in other words, the moon reflects about one-tenth of the light
which falls on it from the sun. He also finds that the light of the full
moon is about twelve times the light of the half moon: a curious and
rather unexpected result.
M. C. Fabry found that during the total eclipse of the sun on August 30,
1905, the light of the corona at a distance of five minutes of arc from
the sun's limit, and in the vicinity of the sun's equator, was about 720
candle-power. Comparing this with the intrinsic light of the full moon
(2600 candle-power) we have the ratio of 0·28 to 1. He finds that the
light of the sun in the zenith, and at its mean distance from the earth,
is 100,000 times greater than the light of a "decimal candle" placed at a
distance of one metre from the eye.[1] He also finds that sunlight is
equal to 60,000 million times the light of Vega. This would make the sun's
"stellar magnitude" minus 26·7, which does not differ much from Prof.
Pickering's result, given above, and is probably not far from the truth.
From experiments made in 1906 at Moscow, Prof. Ceraski found that the
light of the sun's limb is only 31·4 to 38·4 times brighter than the
illumination of the earth's atmosphere very near the limb. This is a very
unexpected result; and considering the comparative faintness of the sun's
corona during a total eclipse, it is not surprising that all attempts to
photograph it without an eclipse have hitherto failed.[2]
From Paschen's investigations on the heat of the sun's surface, he finds a
result of 5961° (absolute), "assuming that the sun is a perfectly black
body."[3] Schuster finds that "There is a stratum near the sun's surface
having an average temperature of approximately 5500° C., to which about
0·3 of the sun's radiation is due. The remaining portion of the radiation
has an intensity equal to that due to a black body having a temperature of
about 6700° C." The above results agree fairly well with those found by
the late Dr. W. E. Wilson.[4] The assumption of the sun being "a black
body" seems a curious paradox; but the simple meaning of the statement is
that the sun is assumed to act as a radiator as _if it were a perfectly
black body heated to the high temperature given above_.
According to Prof. Langley, the sun's photosphere is 5000 times brighter
than the molten metal in a "Bessemer convertor."[5]
Observations of the sun even with small telescopes and protected by dark
glasses are very dangerous to the eyesight. Galileo blinded himself in
this way; Sir William Herschel lost one of his eyes; and some modern
observers have also suffered. The present writer had a narrow escape from
permanent injury while observing the transit of Venus, in 1874, in India,
the dark screen before the eyepiece of a 3-inch telescope having
blistered--that is, partially fused during the observation. Mr. Cooper,
Markree Castle, Ireland, in observing the sun, used a "drum" of alum water
and dark spectacles, and found this sufficient protection against the
glare in using his large refracting telescope of 13·3-inches aperture.
Prof. Mitchell, of Columbia University (U.S.A.), finds that lines due to
the recently discovered atmospherical gases argon and neon are present in
the spectrum of the sun's chromosphere. The evidence for the existence of
krypton and xenon is, however, inconclusive. Prof. Mitchell suggests that
these gases may possibly have reached the earth's atmosphere from the sun.
This would agree with the theory advanced by Arrhenius that "ionised
particles are constantly being repulsed by the pressure of light, and thus
journey from one sun to another."[6]
Prof. Young in 1870, and Dr. Kreusler in June, 1904, observed the helium
line D_{3} as a _dark_ line "in the spectrum of the region about a
sun-spot."[7] This famous line, from which helium was originally
discovered in the sun, and by which it was long afterwards detected in
terrestrial minerals, usually appears as a _bright_ line in the spectrum
of the solar chromosphere and "prominences." It has also been seen _dark_
by Mr. Buss in sun-spot regions.[8]
The discovery of sun-spots was claimed by Hariotte, in 1610, and by
Galileo, Fabricius, and Scheiner, in 1611. The latter wrote 800 pages on
them, and thought they were small planets revolving round the sun! This
idea was also held by Tardè, who called them _Astra Borbonia_, and by C.
Malapert, who termed them _Sydera Austricea_. But they seem to have been
noticed by the ancients.
Although in modern times there has been no extraordinary development of
sun-spots at the epoch of maximum, it is not altogether impossible that in
former times these spots may have occasionally increased to such an
extent, both in number and size, as to have perceptibly darkened the sun's
light. A more probable explanation of recorded sun-darkenings seems,
however, to be the passing of a meteoric or nebulous cloud between the sun
and the earth. A remarkable instance of sun-darkening recorded in Europe
occurred on May 22, 1870, when the sun's light was observed to be
considerably reduced in a cloudless sky in the west of Ireland, by the
late John Birmingham; at Greenwich on the 23rd; and on the same date, but
at a later hour, in North-Eastern France--"a progressive manifestation,"
Mr. Birmingham says, "that seems to accord well with the hypothesis of
moving nebulous matter." A similar phenomenon was observed in New England
(U.S.A.), on September 6, 1881.
One of the largest spots ever seen on the sun was observed in June, 1843.
It remained visible for seven or eight days. According to Schwabe--the
discoverer of the sun-spot period--its diameter was 74,000 miles, so that
its area was many times that of the earth's surface. The most curious
thing about this spot was that it appeared near a _minimum_ of the
sun-spot cycle! and was therefore rather an anomalous phenomenon. It was
suggested by the late Daniel Kirkwood that this great spot was caused by
the fall of meteoric matter into the sun; and that it had possibly some
connection with the great comet of 1843, which approached the sun nearer
than any other recorded comet, its distance from the sun at perihelion
being about 65,000 miles, or less than one-third of the moon's distance
from the earth. This near approach of the comet to the sun occurred about
three months before the appearance of the great sun-spot; and it seems
probable that the spot was caused by the downfall of a large meteorite
travelling in the wake of the comet.[9] The connection between comets and
meteors is well known.
The so-called blackness of sun-spots is merely relative. They are really
very bright. The most brilliant light which can be produced artificially
looks like a black spot when projected on the sun's disc.
According to Sir Robert Ball a pound of coal striking a body with a
velocity of five miles a second would develop as much heat as it would
produce by its combustion. A body falling into the sun from infinity would
have a velocity of 450 miles a second when it reached the sun's surface.
Now as the momentum varies as the square of the velocity we have a pound
of coal developing 90{2} (=450/5){2}, or 8,100 times as much heat as would
be produced by its combustion. If the sun were formed of coal it would be
consumed in about 3000 years. Hence it follows that the contraction of the
sun's substance from infinity would produce a supply of heat for 3000 ×
8100, or 24,300,000 years.
The late Mr. Proctor and Prof. Young believed "that the contraction theory
of the sun's heat is the true and only available theory." The theory is,
of course, a sound one; but it may now be supplemented by supposing the
sun to contain a certain small amount of radium. This would bring physics
and geology into harmony. Proctor thought the "sun's real globe is very
much smaller than the globe we see. In other words the process of
contraction has gone on further than, judging from the sun's apparent
size, we should suppose it to have done, and therefore represents more sun
work" done in past ages.
With reference to the suggestion, recently made, that a portion, at least,
of the sun's heat may be due to radium, and the experiments which have
been made with negative results, Mr. R. T. Strutt--the eminent
physicist--has made some calculations on the subject and says, "even if
all the sun's heat were due to radium, there does not appear to be the
smallest possibility that the Becquerel radiation from it could ever be
detected at the earth's surface."[10]
The eminent Swedish physicist Arrhenius, while admitting that a large
proportion of the sun's heat is due to contraction, considers that it is
probably the chemical processes going on in the sun, and not the
contraction which constitute the _chief_ source of the solar heat.[11]
As the centre of gravity of the sun and Jupiter lies at a distance of
about 460,000 miles from the sun's centre, and the sun's radius is only
433,000 miles, it follows that the centre of gravity of the sun and planet
is about 27,000 miles _outside_ the sun's surface. The attractions of the
other planets perpetually change the position of the centre of gravity of
the solar system; but in some books on astronomy it is erroneously stated
that the centre of gravity of the system is _always_ within the sun's
surface. If _all_ the planets lay on the same side of the sun at the same
time (as might possibly happen), then the centre of gravity of the whole
system would lie considerably more than 27,000 miles outside the sun's
surface.
With reference to the sun's great size, Carl Snyder has well said, "It was
as if in Vulcan's smithy the gods had moulded one giant ball, and the
planets were but bits and small shot which had spattered off as the
glowing ingot was cast and set in space. Little man on a little part of a
little earth--a minor planet, a million of which might be tumbled into the
shell of the central sun--was growing very small; his wars, the
convulsions of a state, were losing consequence. Human endeavour, human
ambitions could now scarce possess the significance they had when men
could regard the earth as the central fact of the universe."[12]
With reference to the late Prof. C. A. Young (U.S.A.)--a great authority
on the sun--an American writer has written the following lines:--
"The destined course of whirling worlds to trace,
To plot the highways of the universe,
And hear the morning stars their song rehearse,
And find the wandering comet in his place;
This is the triumph written in his face,
And in the gleaming eye that read the sun
Like open book, and from the spectrum won
The secrets of immeasurable space."[13]