Astronomical Curiosities Part 3

With reference to the habitability of other planets, Tennyson has beautifully said--

"Venus near her! smiling downwards at this earthlier earth of ours, Closer on the sun, perhaps a world of never fading flowers.

Hesper, whom the poets call'd the Bringer home of all good things; All good things may move in Hesper; perfect people, perfect kings.

Hesper--Venus--were we native to that splendour, or in Mars, We should see the globe we groan in fairest of their evening stars.

Could we dream of war and carnage, craft and madness, l.u.s.t and spite, Roaring London, raving Paris, in that spot of peaceful light?

Might we not in glancing heavenward on a star so silver fair, Yearn and clasp the hands, and murmur, 'Would to G.o.d that we were there!'"

The ancient Greek writer, Diogenes Laertius, states that Anaximander (610-547 B.C.) believed that the earth was a sphere. The Greek words are: ?s?? te t?? ??? ?e?s?a?, ?e?t?? ta??? epe???sa? ??sa? sfa???e?d?.[66]

With reference to the Aurora Borealis, the exact nature of which is not accurately known, "a good story used to be told some years ago of a candidate who, undergoing the torture of a _viva voce_ examination, was unable to reply satisfactorily to any of the questions asked. 'Come, sir,'

said the examiner, with the air of a man asking the simplest question, 'explain to me the cause of the aurora borealis.' 'Sir,' said the unhappy aspirant for physical honours, 'I could have explained it perfectly yesterday, but nervousness has, I think, made me lose my memory.' 'This is very unfortunate,' said the examiner; 'you are the only man who could have explained this mystery, and you have forgotten it.'"[67] This was written in the year 1899, and probably the phenomenon of the aurora remains nearly as great a mystery to-day. In 1839, MM. Bravais and Lottin made observations on the aurora in Norway in about N. lat.i.tude 70. Bravais found the height to be between 62 and 93 miles above the earth's surface.

The cause of the so-called Glacial Epoch in the earth's history has been much discussed. The Russian physicist, Rogovsky, has advanced the following theory--

"If we suppose that the temperature of the sun at the present time is still increasing, or at least has been increasing until now, the glacial epoch can be easily accounted for. Formerly the earth had a high temperature of its own, but received a lesser quant.i.ty of heat from the sun than now; on cooling gradually, the earth's surface attained such a temperature as caused a great part of the surface of the northern and southern hemispheres to be covered with ice; but the sun's radiation increasing, the glaciers melted, and the climatic conditions became as they are now. In a word, the temperature of the earth's surface is a function of two quant.i.ties: one decreasing (the earth's own heat), and the other increasing (the sun's radiation), and consequently there may be a minimum, and this minimum was the glacial epoch, which, as shown by recent investigations, those of Luigi de Marchi (Report of _G. Schiaparelli, Meteorolog. Zeitschr._, 30, 130-136, 1895), are not local, but general for the whole earth" (see also M. Neumahr, _Erdegeschicht_).[68]

Prof. Percival Lowell thinks that the life of geological palaeozoic times was supported by the earth's internal heat, which maintained the ocean at a comparatively warm temperature.[69]

The following pa.s.sage in the Book of the Maccabees may possibly refer to an aurora--

"Now about this time Antiochus made his second inroad into Egypt. And it _so_ befell that throughout all the city, for the s.p.a.ce of almost forty days, there appeared in the midst of the sky hors.e.m.e.n in swift motion, wearing robes inwrought with gold and _carrying_ spears, equipped in troops for battle; and drawing of swords; and _on the other side_ squadrons of horse in array; and encounters and pursuits of both armies; and shaking of shields, and mult.i.tudes of lances, and casting of darts, and flashing of golden trappings, and girding on of all sorts of armour. Wherefore all men besought that the vision might have been given for food."[70]

According to Laplace "the decrease of the mean heat of the earth during a period of 2000 years has not, taking the extremist limits, diminished as much as 1/300th of a degree Fahrenheit."[71]

From his researches on the cause of the Precession of the Equinoxes, Laplace concluded that "the motion of the earth's axis is the same as if the whole sea formed a solid ma.s.s adhering to its surface."[72]

Laplace found that the major (or longer) axis of the earth's...o...b..t coincided with the line of Equinoxes in the year 4107 B.C. The earth's perigee then coincided with the autumnal equinox. The epoch at which the major axis was perpendicular to the line of equinoxes fell in the year 1250 A.D.[73]

Leverrier has found the minimum eccentricity of the earth's...o...b..t round the sun to be 00047; so that the orbit will never become absolutely circular, as some have imagined.

Laplace says--

"Astronomy considered in its entirety is the finest monument of the human mind, the n.o.blest essay of its intelligence. Seduced by the illusions of the senses and of self-pride, for a long time man considered himself as the centre of the movement of the stars; his vain-glory has been punished by the terrors which his own ideas have inspired. At last the efforts of several centuries brushed aside the veil which concealed the system of the world. We discover ourselves upon a planet, itself almost imperceptible in the vast extent of the solar system, which in its turn is only an insensible point in the immensity of s.p.a.ce. The sublime results to which this discovery has led should suffice to console us for our extreme littleness, and the rank which it a.s.signs to the earth. Let us treasure with solicitude, let us add to as we may, this store of higher knowledge, the most exquisite treasure of thinking beings."[74]

With reference to probable future changes in climate, the great physicist, Arrhenius, says--

"We often hear lamentation that the coal stored up in the earth is wasted by the present generation without any thought of the future, and we are terrified by the awful destruction of life and property which has followed the volcanic eruptions of our days. We may find a kind of consolation in the consideration that here, as in every other case, there is good mixed with evil. By the influence of the increasing percentage of carbonic acid in the atmosphere, we may hope to enjoy ages with more equable and better climates, especially as regards the colder regions of the earth, ages when the earth will bring forth much more abundant crops than at present, for the benefit of rapidly propagating mankind."[75]

The night of July 1, 1908, was unusually bright. This was noticed in various parts of England and Ireland, and by the present writer in Dublin.

Humboldt states that "at the time of the new moon at midnight in 1743, the phosph.o.r.escence was so intense that objects could be distinctly recognized at a distance of more than 600 feet."[76]

An interesting proof of the earth's rotation on its axis has recently been found.

"In a paper in the _Proceedings_ of the Vienna Academy (June, 1908) by Herr Tumlirz, it is shown mathematically that if a liquid is flowing outwards between two horizontal discs, the lines of flow will be strictly straight only if the discs and vessel be at rest, and will a.s.sume certain curves if that vessel and the discs are in rotation, as, for example, due to the earth's rotation. An experimental arrangement was set up with all precautions, and the stream lines were marked with coloured liquids and photographed. These were in general accord with the predictions of theory and the supposition that the earth is rotating about an axis."[77]

In a book published in 1905 ent.i.tled _The Rational Almanac_, by Moses B.

Cotsworth, of York, the author states that (p. 397), "The explanation is apparent from the Great Pyramid's Slope, which conclusively proves that when it was built the lat.i.tude of that region was 71 more than at present. Egyptian Memphis now near Cairo was then in lat.i.tude 371, where Asia Minor now ranges, whilst Syria would then be where the Caucasus regions now experience those rigorous winters formerly experienced in Syria." But the reality of this comparatively great change of lat.i.tude in the position of the Great Pyramid can be easily disproved. Pytheas of Ma.r.s.eilles--who lived in the time of Alexander the Great, about 330 B.C.--measured the lat.i.tude of Ma.r.s.eilles by means of a gnomon, and found it to be about 42 56'. As the present lat.i.tude of Ma.r.s.eilles is 43 17'

50", no great change in the lat.i.tude could have taken place in over 2000 years.[78] From this we may conclude that the lat.i.tude of the Great Pyramid has _not_ changed by 71 since its construction. There is, it is true, a slow diminution going on in the obliquity of the ecliptic (or inclination of the earth's axis), but modern observations show that this would not amount to as much as one degree in 6000 years. Eudemus of Rhodes--a disciple of Aristotle (who died in 322 B.C.)--found the obliquity of the ecliptic to be 24, which differs but little from its present value, 23 27'. Al-Sufi in the tenth century measured the lat.i.tude of Schiraz in Persia, and found it 29 36'. Its present lat.i.tude is 29 36' 30",[79] so that evidently there has been no change in the lat.i.tude in 900 years.

CHAPTER V

The Moon

The total area of the moon's surface is about equal to that of North and South America. The actual surface visible at any one time is about equal to North America.

The famous lunar observer, Schroter, thought that the moon had an atmosphere, but estimated its height at only a little over a mile. Its density he supposed to be less than that of the vacuum in an air-pump.

Recent investigations, however, seem to show that owing to its small ma.s.s and attractive force the moon could not retain an atmosphere like that of the earth.

Prof. N. S. Shaler, of Harvard (U.S.A.), finds from a study of the moon (from a geological point of view) with the 15-inch refractor of the Harvard Observatory, that our satellite has no atmosphere nor any form of organic life, and he believes that its surface "was brought to its present condition before the earth had even a solid crust."[80]

There is a curious illusion with reference to the moon's apparent diameter referred to by Proctor.[81] If, when the moon is absent in the winter months, we ask a person whether the moon's diameter is greater or less than the distance between the stars d and e, and e and ? Orionis, the three well-known stars in the "belt of Orion," the answer will probably be that the moon's apparent diameter is about equal to each of these distances. But in reality the apparent distance between d and e Orionis (or between e and ?, which is about the same) is more than double the moon's apparent diameter. This seems at first sight a startling statement; but its truth is, of course, beyond all doubt and is not open to argument.

Proctor points out that if a person estimates the moon as a foot in diameter, as its apparent diameter is about half a degree, this would imply that the observer estimates the circ.u.mference of the star sphere as about 720 feet (360 2), and hence the radius (or the moon's distance from the earth) about 115 feet. But in reality all such estimates have no scientific (that is, accurate) meaning. Some of the ancients, such as Aristotle, Cicero, and Herac.l.i.tus, seem to have estimated the moon's apparent diameter at about a foot.[82] This shows that even great minds may make serious mistakes.

It has been stated by some writer that the moon as seen with the highest powers of the great Yerkes telescope (40 inches aperture) appears "just as it would be seen with the naked eye if it were suspended 60 miles over our heads." But this statement is quite erroneous. The moon as seen with the naked eye or with a telescope shows us nearly a whole hemisphere of its surface. But if the eye were placed only 60 miles from the moon's surface, we should see only a small portion of its surface. In fact, it is a curious paradox that the nearer the eye is to a sphere the less we see of its surface! The truth of this will be evident from the fact that on a level plain an eye placed at a height, say 5 feet, sees a very small portion indeed of the earth's surface, and the higher we ascend the more of the surface we see. I find that at a distance of 60 miles from the moon's surface we should only see a small portion of its visible hemisphere (about 1/90th). The lunar features would also appear under a different aspect. The view would be more of a landscape than that seen in any telescope. This view of the matter is not new. It has been previously pointed out, especially by M. Flammarion and Mr. Whitmell, but its truth is not, I think, generally recognized. Prof. Newcomb doubts whether with any telescope the moon has ever been seen so well as it would be if brought within 500 miles of the earth.

A relief map of the moon 19 feet in diameter was added, in 1898, to the Field Columbian Museum (U.S.A.). It was prepared with great care from the lunar charts of Beer and Madler, and Dr. Schmidt of the Athens Observatory, and it shows the lunar features very accurately. Its construction took five years.

On a photograph of a part of the moon's surface near the crater Eratosthenes, Prof. William H. Pickering finds markings which very much resemble the so-called "ca.n.a.ls" of Mars. The photograph was taken in Jamaica, and a copy of it is given in Prof. Pickering's book on the Moon, and in _Popular Astronomy_, February, 1904.

Experiments made in America by Messrs. Stebbins and F. C. Brown, by means of selenium cells, show that the light of the full moon is about nine times that of the half moon;[83] and that "the moon is brighter between the first quarter and full than in the corresponding phase after full moon." They also find that the light of the full moon is equal to "023 candle power,"[83] that is, according to the method of measurement used in America, its light is equal to 023 of a standard candle placed at a distance of one metre (3937 inches) from the eye.[84]

Mr. H. H. Kimball finds that no less than 52 per cent. of the observed changes in intensity of the "earth-shine" visible on the moon when at or near the crescent phase is due to the eccentricity of the lunar orbit, and "this is probably much greater than could be expected from any increase or diminution in the average cloudiness over the hemisphere of the earth reflecting light to the moon."[85]

The "moon maiden" is a term applied to a fancied resemblance of a portion of the Sinus Iridum to a female head. It forms the "promontory" known as Cape Heraclides, and may be looked for when the moon's "age" is about 11 days. Mr. C. J. Caswell, who observed it on September 29, 1895, describes it as resembling "a beautiful silver statuette of a graceful female figure with flowing hair."

M. Landerer finds that the angle of polarization of the moon's surface--about 33--agrees well with the polarizing angle for many specimens of igneous rocks (30 51' to 33 46'). The polarizing angle for ice is more than 37, and this fact is opposed to the theories of lunar glaciation advanced by some observers.[86]

Kepler states in his _Somnium_ that he saw the moon in the crescent phase on the morning and evening of the _same_ day (that is, before and after conjunction with the sun). Kepler could see 14 stars in the Pleiades with the naked eye, so his eyesight must have been exceptionally keen.

Investigations on ancient eclipses of the moon show that the eclipse mentioned by Josephus as having occurred before the death of Herod is probably that which took place on September 15, B.C. 5. This occurred about 9.45 p.m.; and probably about six months before the death of Herod (St. Matthew ii. 15).

The total lunar eclipse which occurred on October 4, 1884, was remarkable for the almost total disappearance of the moon during totality. One observer says that "in the open air, if one had not known exactly where to look for it, one might have searched for some time without discovering it.

I speak of course of the naked eye appearance."[87] On the other hand the same observer, speaking of the total eclipse of the moon on August 23, 1877, which was a bright one, says--

"The moon even in the middle of the total phase was a conspicuous object in the sky, and the ruddy colour was well marked. In the very middle of the eclipse the degree of illumination was as nearly as possible equal all round the edge of the moon, the central parts being darker than those near the edge."

In Roger de Hovedin's _Chronicle_ (A.D. 756) an account is given of the occultation of "a bright star," by the moon during a total eclipse. This is confirmed by Simeon of Durham, who also dates the eclipse A.D. 756.

This is, however, a mistake, the eclipse having occurred on the evening of November 23, A.D. 755. Calvisius supposed that the occulted "star" might have been Aldebaran. Pingre, however, showed that this was impossible, and Struyck, in 1740, showed that the planet Jupiter was the "star" referred to by the early observer. Further calculations by Hind (1885) show conclusively that Struyck was quite correct, and that the phenomenon described in the old chronicles was the occultation of Jupiter by a totally eclipsed moon--a rather unique phenomenon.[88]

An occultation of Mars by the moon is recorded by the Chinese, on February 14, B.C. 69, and one of Venus, on March 30, A.D. 361. These have also been verified by Hind, and his calculations show the accuracy of these old Chinese records.

It has been suggested that the moon may possibly have a satellite revolving round it, as the moon itself revolves round the earth. This would, of course, form an object of great interest. During the total lunar eclipses of March 10 and September 3, 1895, a careful photographic search was made by Prof. Barnard for a possible lunar satellite. The eclipse of March 10 was not very suitable for the purpose owing to a hazy sky, but that of September 3 was "entirely satisfactory," as the sky was very clear, and the duration of totality was very long. On the latter occasion "six splendid" photographs were obtained of the total phase with a 6-inch Willard lens. The result was that none of these photographs "show anything which might be taken for a lunar satellite," at least any satellite as bright as the 10th or 12th magnitude. It is, of course, just possible that the supposed satellite might have been behind the moon during the totality.

With reference to the attraction between the earth and moon, Sir Oliver Lodge says--