Astronomical Curiosities Part 4

"The force with which the moon is held in its...o...b..t would be great enough to tear asunder a steel rod 400 miles thick, with a tenacity of 30 tons to the square inch, so that if the moon and earth were connected by steel instead of gravity, a forest of pillars would be necessary to whirl the system once a month round their common centre of gravity. Such a force necessarily implies enormous tensure or pressure in the medium. Maxwell calculates that the gravitational stress near the earth, which we must suppose to exist in the invisible medium, is 3000 times greater than what the strongest steel can stand, and near the sun it should be 2500 times as great as that."[89]

With reference to the names given to "craters" on the moon, Prof. W. H.

Pickering says,[90] "The system of nomenclature is, I think, unfortunate.

The names of the chief craters are generally those of men who have done little or nothing for selenography, or even for astronomy, while the men who should be really commemorated are represented in general by small and unimportant craters," and again--

"A serious objection to the whole system of nomenclature lies in the fact that it has apparently been used by some selenographers, from the earliest times up to the present, as a means of satisfying their spite against some of their contemporaries. Under the guise of pretending to honour them by placing their names in perpetuity upon the moon, they have used their names merely to designate the smallest objects that their telescopes were capable of showing. An interesting ill.u.s.tration of this point is found in the craters of Galileo and Riccioli, which lie close together on the moon. It will be remembered that Galileo was the discoverer of the craters on the moon. Both names were given by Riccioli, and the relative size and importance of the craters [Riccioli large, and Galileo very small] probably indicates to us the relative importance that he a.s.signed to the two men themselves. Other examples might be quoted of craters named in the same spirit after men still living.... With the exception of Maedler, one might almost say, the more prominent the selenographer the more insignificant the crater."

The mathematical treatment of the lunar theory is a problem of great difficulty. The famous mathematician, Euler, described it as _incredibile stadium atque indefessus labor_.[91]

With reference to the "earth-s.h.i.+ne" on the moon when in the crescent phase, Humboldt says, "Lambert made the remarkable observation (14th of February, 1774) of a change of the ash-coloured moonlight into an olive-green colour, bordering upon yellow. The moon, which then stood vertically over the Atlantic Ocean, received upon its night side the green terrestrial light, which is reflected towards her when the sky is clear by the forest districts of South America."[92] Arago said, "Il n'est donc pas impossible, malgre tout ce qu'un pareil resultat exciterait de surprise au premier coup d'il qu'un jour les meteorologistes aillent puiser dans l'aspect de la Lune des notions precieuses sur _l'etat moyen_ de diaphanite de l'atmosphere terrestre, dans les hemispheres qui successivement concurrent a la production de la lumiere cendree."[93]

The "earth-s.h.i.+ne" on the new moon was successfully photographed in February, 1895, by Prof. Barnard at the Lick Observatory, with a 6-inch Willard portrait lens. He says--

"The earth-lit globe stands out beautifully round, encircled by the slender crescent. All the 'seas' are conspicuously visible, as are also the other prominent features, especially the region about _Tycho_. _Aristarchus_ and _Copernicus_ appear as bright specks, and the light streams from _Tycho_ are very distinct."[94]

Kepler found that the moon completely disappeared during the total eclipse of December 9, 1601, and Hevelius observed the same phenomenon during the eclipse of April 25, 1642, when "not a vestige of the moon could be seen."[95] In the total lunar eclipse of June 10, 1816, the moon during totality was not visible in London, even with a telescope![95]

The lunar mountains are _relatively_ much higher than those on the earth.

Beer and Madler found the following heights: Dorfel, 23,174 feet; Newton, 22,141; Casatus, 21,102; Curtius, 20,632; Callippus, 18,946; and Tycho, 18,748 feet.[96]

Taking the earth's diameter at 7912 miles, the moon's diameter, 2163 miles, and the height of Mount Everest as 29,000 feet, I find that

Everest 1 Dorfel 1 ---------------- = ----, and --------------- = --- Earth's diameter 1440 moon's diameter 492

From which it follows that the lunar mountains are _proportionately_ about three times higher than those on the earth.

According to an hypothesis recently advanced by Dr. See, all the satellites of the solar system, including our moon, were "captured" by their primaries. He thinks, therefore, that the "moon came to earth from heavenly s.p.a.ce."[97]

CHAPTER VI

Mars

Mars was called by the ancients "the vanis.h.i.+ng star," owing to the long periods during which it is practically invisible from the earth.[98] It was also called p???e?? and Hercules.

I have seen it stated in a book on the "Solar System" by a well-known astronomer that the _axis_ of Mars "is inclined to the plane of the orbit"

at an angle of 24 50'! But this is quite erroneous. The angle given is the angle between _the plane of the planet's equator_ and the plane of its...o...b..t, which is quite a different thing. This angle, which may be called the obliquity of Mars' ecliptic, does not differ much from that of the earth. Lowell finds it 23 13' from observations in 1907.[99]

The late Mr. Proctor thought that Mars is "far the reddest star in the heavens; Aldebaran and Antares are pale beside him."[100] But this does not agree with my experience. Antares is to my eye quite as red as Mars.

Its name is derived from two Greek words implying "redder than Mars." The colour of Aldebaran is, I think, quite comparable with that of the "ruddy planet." In the telescope the colour of Mars is, I believe, more yellow than red, but I have not seen the planet very often in a telescope. Sir John Herschel suggested that the reddish colour of Mars may possibly be due to red rocks, like those of the Old Red Sandstone, and the red soil often a.s.sociated with such rocks, as I have myself noticed near Torquay and other places in Devons.h.i.+re.

The ruddy colour of Mars was formerly thought to be due to the great density of its atmosphere. But modern observations seem to show that the planet's atmosphere is, on the contrary, much rarer than that of the earth. The persistent visibility of the markings on its surface shows that its atmosphere cannot be cloud-laden like ours; and the spectroscope shows that the water vapour present is--although perceptible--less than that of our terrestrial envelope.

The existence of water vapour is clearly shown by photographs of the planet's spectrum taken by Mr. Slipher at the Lowell Observatory in 1908.

These show that the water vapour bands _a_ and near D are stronger in the spectrum of Mars than in that of the moon at the same alt.i.tude.[101]

The dark markings on Mars were formerly supposed to represent water and the light parts land. But this idea has now been abandoned. Light reflected from a water surface is polarized at certain angles. Prof. W. H.

Pickering, in his observations on Mars, finds no trace of polarization in the light reflected from the dark parts of the planet. But under the same conditions he finds that the bluish-black ring surrounding the white polar cap shows a well-marked polarization of light, thus indicating that this dark ring is probably water.[102]

Projections on the limb of the planet have frequently been observed in America. These are known _not_ to be mountains, as they do not reappear under similar conditions. They are supposed to be clouds, and one seen in December, 1900, has been explained as a cloud lying at a height of some 13 miles above the planet's surface and drifting at the rate of about 27 miles an hour. If there are any mountains on Mars they have not yet been discovered.

The existence of the so-called "ca.n.a.ls" of Mars is supposed to be confirmed by Lowell's photographs of the planet. But what these "ca.n.a.ls"

really represent, that is the question. They have certainly an artificial look about them, and they form one of the most curious and interesting problems in the heavens. Prof. Lowell says--

"Most suggestive of all Martian phenomena are the ca.n.a.ls. Were they more generally observable the world would have been spared much scepticism and more theory. They may of course not be artificial, but observations here [Flagstaff] indicate that they are; as will, I think, appear from the drawings. For it is one thing to see two or three ca.n.a.ls and quite another to have the planet's disc mapped with them on a most elaborate system of triangulation. In the first place they are this season (August, 1894) bluish-green, of the same colour as the seas into which the longer ones all eventually debouch. In the next place they are almost without exception geodetically straight, supernaturally so, and this in spite of their leading in every possible direction. Then they are of apparently nearly uniform width throughout their length. What they are is another matter. Their mere aspect, however, is enough to cause all theories about glaciation fissures or surface cracks to die an instant and natural death."[103]

Some of the observed colour-changes on Mars are very curious. In April, 1905, Mr. Lowell observed that the marking known as Mare Erythraeum, just above Syrtis, had "changed from a blue-green to a chocolate-brown colour."

The season on Mars corresponded with our February.

Signor V. Cerulli says that, having observed Mars regularly for ten years, he has come to the conclusion that the actual existence of the "ca.n.a.ls" is as much a subject for physiological as for astronomical investigation. He states that "the phenomena observed are so near the limit of the range of the human eye that in observing them one really experiences an effect accompanying the 'birth of vision.' That is to say, the eye sees more and more as it becomes accustomed, or strained, to the delicate markings, and thus the joining up of spots to form 'ca.n.a.ls' and the gemination of the latter follow as a physiological effect, and need not necessarily be subjective phenomena seen by the unaccustomed eye."[104]

The possibility of life on Mars has been recently much discussed; some denying, others a.s.serting. M. E. Rogovsky says--

"As free oxygen and carbonic dioxide may exist in the atmosphere of _Mars_, vegetable and animal life is quite possible. If the temperature which prevails upon _Mars_ is nearer to -36 C. than to -73 C., the existence of living beings like ourselves is possible. In fact, the ice of some Greenland and Alpine glaciers is covered by red algae (_Sphaerella nivalis_); we find there also different species of rotaloria, variegated spiders, and other animals on the snow fields illuminated by the sun; at the edges of glacier snows in the Tyrol we see violet bells of _Soldanella pusilla_, the stalks of which make their way through the snow by producing heat which melts it round about them. Finally the Siberian town Verkhociansk, near Yakutsk, exists, though the temperature there falls to -698 C. and the mean temperature of January to -512, and the mean pressure of the vapour of water is less than 005mm. It is possible, therefore, that living beings have become adapted to the conditions now prevailing upon _Mars_ after the lapse of many ages, and live at an even lower temperature than upon the earth, developing the necessary heat themselves."

M. Rogovsky adds, "Water in organisms is mainly a liquid or solvent, and many other liquids may be the same. We have no reason to believe that life is possible only under the same conditions and with the same chemical composition of organisms as upon the earth, although indeed we cannot affirm that they actually exist on Mars."[105] With the above views the present writer fully concurs.

Prof. Lowell thinks that the polar regions of Mars, both north and south, are actually warmer than the corresponding regions of the earth, although the mean temperature of the planet is probably twelve degrees lower than the earth's mean temperature.[106]

A writer in _Astronomy and Astrophysics_ (1892, p. 748) says--

"Whether the planet Mars is inhabited or not seems to be the all-absorbing question with the ordinary reader. With the astronomer this query is almost the last thing about the planet that he would think of when he has an opportunity to study its surface markings ...

no astronomer claims to know whether the planet is inhabited or not."

Several suggestions have been made with reference to the possibility of signalling to Mars. But, as Mr. Larkin of Mount Lowe (U.S.A.) points out, all writers on this subject seem to forget the fact that the night side of two planets are never turned towards each other. "When the sun is between them it is day on the side of Mars which is towards us, and also day on the side of the earth which is towards Mars. When they are on the same side of the sun, it is day on Mars when night on the earth, and for this reason they could never see our signals. This should make it apparent that the task of signalling to Mars is a more difficult one than the most hopeful theorist has probably considered. All this is under the supposition that the Martians (if there are such) are beings like ourselves. If they are not like us, we cannot guess what they are like."[107] These views seem to me to be undoubtedly correct, and show the futility of visual signals. Electricity might, however, be conceivably used for the purpose; but even this seems highly improbable.

Prof. Newcomb, in his work _Astronomy for Everybody_, says with reference to this question, "The reader will excuse me from saying nothing in this chapter about the possible inhabitants of Mars. He knows just as much about the subject as I do, and that is nothing at all."

It is, however, quite possible that life _in some form_ may exist on Mars.

As Lowell well says, "Life but waits in the wings of existence for its cue to enter the scene the moment the stage is set."[108] With reference to the "ca.n.a.ls" he says--

"It is certainly no exaggeration to say that they are the most astonis.h.i.+ng objects to be viewed in the heavens. There are celestial sights more dazzling, spectacles that inspire more awe, but to the thoughtful observer who is privileged to see them well, there is nothing in the sky so profoundly impressive as these ca.n.a.ls of Mars."[109]

The eminent Swedish physicist Arrhenius thinks that the mean annual temperature on Mars may possibly be as high as 50 F. He says, "Sometimes the snow-caps on the poles of Mars disappear entirely during the Mars summer; this never happens on our terrestrial poles. The mean temperature of Mars must therefore be above zero, probably about +10 [Centigrade = 50 Fahrenheit]. Organic life may very probably thrive, therefore, on Mars."[110] He thinks that this excess of mean temperature above the calculated temperature may be due to an increased amount of carbonic acid in the planet's atmosphere, and says "any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth's surface by 4; and if the carbon dioxide were increased fourfold, the temperature would rise by 8."[111]

Denning says,--[112]

"A few years ago, when christening celestial formations was more in fas.h.i.+on than it is now, a man simply had to use a telescope for an evening or two on Mars or the moon, and spice the relation of his seeings with something in the way of novelty, when his name would be pretty certainly attached to an object and hung in the heavens for all time! A writer in the _Astronomical Register_ for January, 1879, humorously suggested that 'the matter should be put into the hands of an advertising agent,' and 'made the means of raising a revenue for astronomical purposes.' Some men would not object to pay handsomely for the distinction of having their names applied to the seas and continents of Mars or the craters of the moon."

An occultation of Mars by the moon is recorded by Aristotle as having occurred on April 4, 357 B.C.[113]

Seen from Mars the maximum apparent distance between the earth and moon would vary from 3' to nearly 17'.[114]