Astronomical Curiosities: Facts and Fallacies

Some of the observed colour-changes on Mars are very curious. In April, 1905, Mr. Lowell observed that the marking known as Mare Erythræum, 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 “canals” 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 ‘canals’ and the gemination of the latter follow as a physiological effect, and need not necessarily be subjective phenomena seen by the unaccustomed eye.”[103 - Nature, April 20, 1905.]

The possibility of life on Mars has been recently much discussed; some denying, others asserting. 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 algæ (Sphærella 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 -69°·8 C. and the mean temperature of January to -51°·2, and the mean pressure of the vapour of water is less than 0·05mm. 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.”[104 - Astrophysical Journal, vol. 14 (1901), p. 258.] 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.[105 - Nature, August 22, 1907.]

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.”[106 - Popular Astronomy, vol. 12 (1904), p. 679.] 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.”[107 - Mars as an Abode of Life, p. 69.] With reference to the “canals” he says —

“It is certainly no exaggeration to say that they are the most astonishing 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 canals of Mars.”[108 - Ibid., p. 146.]

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.”[109 - Worlds in the Making, p. 49.] 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°.”[110 - Worlds in the Making, p. 53.]

Denning says, —[111 - Denning, Telescopic Work for Starlight Evenings, p. 158.]

“A few years ago, when christening celestial formations was more in fashion 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.[112 - Ibid., p. 166.]

Seen from Mars the maximum apparent distance between the earth and moon would vary from 3½′ to nearly 17′.[113 - Nature, July 13, 1876.]

CHAPTER VII

The Minor Planets

Up to 1908 the number of minor planets (or asteroids) certainly known amounted to over 650.

From an examination of the distribution of the first 512 of these small bodies, Dr. P. Stroobant finds that a decided maximum in number occurs between the limits of distance of 2·55 and 2·85 (earth’s mean distance from sun = 1), “199 of the asteroids considered revolving in this annulus.” He finds that nearly all the asteroidal matter is concentrated near to the middle of the ring in the neighbourhood of the mean distance of 2·7, and the smallest asteroids are relatively less numerous in the richest zones.[114 - Nature, May 2, 1907.]

There are some “striking similarities” in the orbits of some of the asteroids. Thus, in the small planets Sophia (No. 251 in order of discovery) and Magdalena (No. 318) we have the mean distance of Sophia 3·10, and that of Magdalena 3·19 (earth’s mean distance = 1). The eccentricities of the orbits are 0·09 and 0·07; and the inclinations of the orbits to the plane of the ecliptic 10° 29′ and 10° 33′ respectively.[115 - Nature, May 30, 1907.] This similarity may be – and probably is – merely accidental, but it is none the less curious and interesting.

Some very interesting discoveries have recently been made among the minor planets. The orbit of Eros intersects the orbit of Mars; and the following have nearly the same mean distance from the sun as Jupiter: —

Achilles (1906 TG), No. 588,

Patrocles (1906 XY), No. 617,

Hector (1907 XM), No. 624,

and another (No. 659) has been recently found. Each of these small planets “moves approximately in a vertex of an equilateral triangle that it forms with Jupiter and the sun.”[116 - Publications of the Astronomical Society of the Pacific, August, 1908.] The minor planet known provisionally as HN is remarkable for the large eccentricity of its orbit (0·38), and its small perihelion distance (1·6). When discovered it had a very high South Declination (61½°), showing that the inclination of the plane of its orbit to the plane of the ecliptic is considerable.[117 - Monthly Notices, R.A.S., 1902, p. 291.]

Dr. Bauschinger has made a study of the minor planets discovered up to the end of 1900. He finds that the ascending nodes of the orbits show a marked tendency to cluster near the ascending node of Jupiter’s orbit, a fact which agrees well with Prof. Newcomb’s theoretical results. There seems to be a slight tendency for large inclinations and great eccentricities to go together; but there appears to be no connection between the eccentricity and the mean distance from the sun. The longitudes of the perihelia of these small planets “show a well-marked maximum near the longitude of Jupiter’s perihelion, and equally well-marked minimum near the longitude of his aphelion,” which is again in good agreement with Newcomb’s calculations.[118 - Monthly Notices, R.A.S., February, 1902, p. 291.] Dr. Bauschinger’s diameter for Eros is 20 miles. He finds that the whole group, including those remaining to be discovered, would probably form a sphere of about 830 miles in diameter.

The total mass of the minor planets has been frequently estimated, but generally much too high. Mr. B. M. Roszel of the John Hopkins University (U.S.A.) has made a calculation of the probable mass from the known diameter of Vesta (319 miles, Pickering), and finds the volume of the first 216 asteroids discovered. From this calculation it appears that it would take 310 asteroids of the 6th magnitude, or 1200 of the 7th to equal the moon in volume. Mr. Roszel concludes that the probable mass of the whole asteroidal belt is between 1⁄50th and 1⁄100th of that of the moon.[119 - Nature, May 24, 1894.] Subsequently Mr. Roszel extended his study to the mass of 311 asteroids,[120 - Ibid., February 14, 1895.] and found a combined mass of about 1⁄40th of the moon’s mass.

Dr. Palisa finds that the recently discovered minor planet (1905 QY) varies in light to a considerable extent.[121 - Ibid., September 14, 1905.] This planet was discovered by Dr. Max Wolf on August 23, 1905; but it was subsequently found that it is identical with one previously known, (167) Urda.[122 - Ibid., September 21, 1905.] The light variation is said to be from the 11th to the 13th magnitude.[123 - Ibid., September 28, 1905.] Variation in some of the other minor planets has also been suspected. Prof. Wendell found a variation of about half a magnitude in the planet Eunomia (No. 15). He also found that Iris (No. 7) varies about a quarter of a magnitude in a period of about 6h 12m.[124 - Ibid., July 13, 1905.] But these variations are small, and perhaps doubtful. The variability of Eros is well known.

The planet Eros is a very interesting one. The perihelion portion of its orbit lies between the orbits of Mars and the earth, and the aphelion part is outside the orbit of Mars. Owing to the great variation in its distance from the earth the brightness of Eros varies from the 6th to the 12th magnitude. That is, when brightest, it is 250 times brighter than when it is faintest.[125 - Nature, November 3, 1898.] This variation of light, is of course, merely due to the variation of distance; but some actual variation in the brightness of the planet has been observed.

It has been shown by Oeltzen and Valz that Cacciatore’s supposed distant comet, mentioned by Admiral Smyth in his Bedford Catalogue, must have been a minor planet.[126 - Ibid., July 14, 1881, p. 235.]

Dr. Max Wolf discovered 36 new minor planets by photography in the years 1892-95. Up to the latter year he had never seen one of these through a telescope! His words are, “Ich selsbt habe noch nie einen meinen kleinen Planeten am Himmel gesehen.”[127 - Quoted in The Observatory, February, 1896, p. 104, from Ast. Nach., No. 3319.]

These small bodies have now become so numerous that it is a matter of much difficulty to follow them. At the meeting of the Royal Astronomical Society on January 8, 1909, Mr. G. F. Chambers made the following facetious remarks —

“I would like to make a suggestion that has been in my mind for several years past – that it should be made an offence punishable by fine or imprisonment to discover any more minor planets. They seem to be an intolerable nuisance, and are a great burden upon the literary gentlemen who have to keep pace with them and record them. I have never seen, during the last few years at any rate, any good come from them, or likely to come, and I should like to see the supply stopped, and the energies of the German gentlemen who find so many turned into more promising channels.”

Among the minor planets numbered 1 to 500, about 40 “have not been seen since the year of their discovery, and must be regarded as lost.”[128 - Monthly Notices, R.A.S., February, 1909.]

CHAPTER VIII

Jupiter

This brilliant planet – only inferior to Venus in brightness – was often seen by Bond (Jun.) with the naked eye in “high and clear sunshine”; also by Denning, who has very keen eyesight. Its brightness on such occasions is so great, that – like Venus – it casts a distinct shadow in a dark room.[129 - Celestial Objects, vol. i. p. 163.]

The great “red spot” on Jupiter seems to have been originally discovered by Robert Hooke on May 9, 1664, with a telescope of 2 inches aperture and 12 feet focus. It seems to have existed ever since; at least the evidence is, according to Denning, in favour of the identity of Hooke’s spot with the red spot visible in recent years. The spot was also observed by Cassini in the years 1665-72, and is sometimes called “Cassini’s spot.” But the real discoverer was Hooke.[130 - Nature, December 29, 1898.]

The orbit of Jupiter is so far outside the earth’s orbit that there can be little visible in the way of “phase” – as in the case of Mars, where the “gibbous” phase is sometimes very perceptible. Some books on astronomy state that Jupiter shows no phase. But this is incorrect. A distinct, although very slight, gibbous appearance is visible when the planet is near quadrature. Webb thought it more conspicuous in twilight than in a dark sky. With large telescopes, Jupiter’s satellites II. and III. have been seen – in consequence of Jupiter’s phase – to emerge from occultation “at a sensible distance from the limb.”[131 - Celestial Objects, vol. i. p. 166.]

According to M. E. Rogovsky, the high “albedo of Jupiter, the appearance of the clear (red) and dark spots on its surface and their continual variation, the different velocity of rotation of the equatorial and other zones of its surface, and particularly its small density (1·33, water as unity), all these facts afford irrefragable proofs of the high temperature of this planet. The dense and opaque atmosphere hides its glowing surface from our view, and we see therefore only the external surface of its clouds. The objective existence of this atmosphere is proved by the bands and lines of absorption in its spectrum. The interesting photograph obtained by Draper, September 27, 1879, in which the blue and green parts are more brilliant for the equatorial zone than for the adjacent parts of the surface, appears to show that Jupiter emits its proper light. It is possible that the constant red spot noticed on its surface by several observers, as Gledhill, Lord Rosse, and Copeland (1873), Russel and Bredikhin (1876), is the summit of a high glowing mountain. G. W. Hough considers Jupiter to be gaseous, and A. Ritter inferred from his formulæ that in this case the temperature at the centre would be 600,000 °C.”[132 - Astrophysical Journal, vol. 14 (1901), pp. 248-9.]

The four brighter satellites of Jupiter are usually known by numbers I., II., III., and IV.; I. being the nearest to the planet, and IV. the farthest. III. is usually the brightest, and IV. the faintest, but exceptions to this rule have been noticed.

With reference to the recently discovered sixth and seventh satellites of Jupiter, Prof. Perrine has suggested that the large inclination of their orbits to the plane of the planet’s equator seems to indicate that neither of these bodies was originally a member of Jupiter’s family, but has been “captured by the planet.” This seems possible as the orbits of some of the minor planets lie near the orbit of Jupiter (see “Minor Planets”). A similar suggestion has been made by Prof. del Marmol.[133 - Nature, August 27, 1908.]

Many curious observations have been recorded with reference to Jupiter’s satellites; some very difficult of explanation. In 1711 Bianchini saw satellite IV. so faint for more than an hour that it was hardly visible! A similar observation was made by Lassell with a more powerful telescope on June 13, 1849. Key, T. T. Smyth, and Denning have also recorded unusual faintness.[134 - Webb’s Celestial Objects, vol. i. p. 177.] A very remarkable phenomenon was seen by Admiral Smyth, Maclear, and Pearson on June 26, 1828. Satellite II., “having fairly entered on Jupiter, was found 12 or 13 minutes afterwards outside the limb, where it remained visible for at least 4 minutes, and then suddenly vanished.” As Webb says, “Explanation is here set at defiance; demonstrably neither in the atmosphere of the earth, nor Jupiter, where and what could have been the cause? At present we can get no answer.”[135 - Ibid., vol. i. p. 187.] When Jupiter is in opposition to the sun – that is, on the meridian at midnight – satellite I. has been seen projected on its own shadow, the shadow appearing as a dark ring round the satellite.

On January 28, 1848, at Cambridge (U.S.A.) satellite III. was seen in transit lying between the shadows of I. and II. and so black that it could not be distinguished from the shadows, “except by the place it occupied.” This seems to suggest inherent light in the planet’s surface, as the satellite was at the time illuminated by full sunshine; its apparent blackness being due to the effect of contrast. Cassini on one occasion failed to find the shadow of satellite I. when it should have been on the planet’s disc,[136 - Celestial Objects, vol. i. p. 186.] an observation which again points to the glowing light of Jupiter’s surface. Sadler and Trouvelot saw the shadow of satellite I. double! an observation difficult to explain – but the same phenomenon was again seen on the evening of September 19, 1891, by Mr. H. S. Halbert of Detroit, Michigan (U.S.A.). He says that the satellite “was in transit nearing egress, and it appeared as a white disc against the dark southern equatorial belt; following it was the usual shadow, and at an equal distance from this was a second shadow, smaller and not so dark as the true one, and surrounded by a faint penumbra.”[137 - Astronomy and Astrophysics, 1892, p. 87.]

A dark transit of satellite III. was again seen on the evening of December 19, 1891, by two observers in America. One observer noted that the satellite, when on the disc of the planet, was intensely black. To the other observer (Willis L. Barnes) it appeared as an ill-defined dark image.[138 - Ibid., 1892, pp. 94-5.] A similar observation was made on October 9 of the same year by Messrs. Gale and Innes.[139 - Observatory, December, 1891.]

A “black transit” of satellite IV. was seen by several observers in 1873, and by Prof. Barnard on May 4, 1886. The same phenomenon was observed on October 30, 1903, in America, by Miss Anne S. Young and Willis S. Barnes. Miss Young says —

“The ingress of the satellite took place at 8h 50m (E. standard time) when it became invisible upon the background of the planet. An hour later it was plainly visible as a dark round spot upon the planet. It was decidedly darker than the equatorial belt.”[140 - Popular Astronomy, vol. 11 (1903), p. 574.]

The rather rare phenomenon of an occultation of one of Jupiter’s satellites by another was observed by Mr. Apple, director of the Daniel Scholl Observatory, Franklin and Marshall College, Lancaster, Pa. (U.S.A.), on the evening of March 16, 1908. The satellites in question were I. and II., and they were so close that they could not be separated with the 11·5-inch telescope of the Observatory.[141 - Ibid., October, 1908.] One of the present writer’s first observations with a telescope is dated May 17, 1873, and is as follows: “Observed one of Jupiter’s satellites occulted (or very nearly so) by another. Appeared as one with power 133” (on 3-inch refractor in the Punjab). These satellites were probably I. and II.