Astronomy for Amateurs

violet remains visible after the red. This experiment shows that the last light emitted by the eclipsed Sun belongs to the least refrangible rays, to the greatest wave-lengths, to the slowest vibrations, to the yellow and red rays. Such therefore is the predominating color of the solar atmosphere. This experiment completed, we turn back to the Sun. Magical and splendid spectacle! Totality has commenced, the Sun has disappeared, the black disk of the Moon covers it entirely, leaving all round it a magnificent corona of dazzling light. One would suppose it to be an annular eclipse, with the difference that this can be observed with the naked eye, without fatigue to the retina, and drawn quietly. This luminous coronal atmosphere entirely surrounds the solar disk, at a pretty equal depth, equivalent to about the third of half the solar diameter. It may be regarded as the Sun's atmosphere. Beyond this corona is an aureole, of vaster glory but less luminous, which sends out long plumes, principally in the direction of the equatorial zone of the Sun, and of the belt of activity of the spots and prominences. [Pg 280] At the summit of the disk it is conical in shape. Below it is double, and its right-hand portion ends in a point, not far from Mercury, which shines like a dazzling star of first magnitude, and seems placed there expressly to give us the extent and direction of the solar aureole. I draw these various aspects (which, moreover, change with the movement of the Moon), and what strikes me most is the distinction in light between this aureole and the coronal atmosphere; the latter appears to be a brilliant silvery white, the former is grayer and certainly less dense. My impression is that there are two solar envelopes of entirely different nature, the corona belonging to the globe of the Sun, and forming its atmosphere properly so-called, very luminous; the aureole formed of particles that circulate independently round it, probably arising from eruptions, their form as a whole being possibly due to electric or magnetic forces, counterbalanced by resistances of various natures. In our own atmosphere the volcanic eruptions are distinct from the aerial envelope. The general configuration of this external halo, spreading more particularly in the equatorial zone, is sufficiently like that of the eclipse of 1889, published in my Popular Astronomy, which also corresponded with a minimum of solar energy. The year 1900 is in fact close upon the minimum of the eleven-year period. This equatorial form is, moreover, what all the astronomers were expecting. [Pg 281] Fig. 78.—Total eclipse of the Sun, May 28, 1900, as observed from Elche (Spain). [Pg 282] There can no longer be the slightest doubt that the solar envelope varies with the activity of the Sun.... "But the total eclipse lasted a much shorter time than I have taken to write these lines. The seventy-nine seconds of totality are over. A dazzling light bursts from the Sun, and tells that the Moon pursuing its orbit has left it. The splendid sight is over. It has gone like a shadow. "Already over! It is almost a disillusion. Nothing beautiful lasts in this world. Too sad! If only the celestial spectacle could have lasted two, three, or four minutes! It was too short.... "Alas! we are forced to take things as they are. "The surprise, the oppression, the terror of some, the universal silence are over. The Sun reappears in his splendor, and the life of nature resumes its momentarily suspended course. "While I was making my drawing, M. l'Abbé Moreux, my colleague from the Astronomical Society of France, who accompanied me to Spain for this observation, was taking one of his own, without any reciprocal communication. These two sketches are alike, and confirmatory. [Pg 283] "The differential thermometers that I exposed to the Sun, hanging freely, and protected from reflection from the ground, were read every five minutes. The black thermometer went down from 33.1° to 20.7°, that is 12.4°; the white from 29° to 20.2°—that is, 8.8°. The temperature in the shade only varied three degrees. "The light received during totality was due: first, to the luminous envelope of the Sun; second, to that of the terrestrial atmosphere, illuminated at forty kilometers (twenty-five miles) on the one side and the other of the line of centrality. It appeared to be inferior to that of the Full Moon, on account of the almost sudden transition. But, in reality, it was more intense, for only first-magnitude stars were visible in the sky, whereas on a night of full moon, stars of second, and even of third magnitude are visible. We recognized, among others, Venus, Mercury, Sirius, Procyon, Capella, Rigel, Betelgeuse." From these notes, taken on the spot, it is evident that the contemplation of a total eclipse of the Sun is one of the most marvelous spectacles that can be admired upon our planet. Some persons assured me that they saw the shadow of the Moon flying rapidly over the landscape. My attention was otherwise occupied, and I was unable to[Pg 284] verify this interesting observation. The shadow of the Moon in effect took only eleven minutes (3.47 P.M. to 3.58 P.M.) to traverse the Iberian Peninsula from Porto to Alicante, i.e., a distance of 766 kilometers (475 miles). It must therefore have passed over the ground at a velocity of sixty-nine kilometers per minute, or 1,150 meters per second, a speed higher than that of a bullet. It can easily be watched from afar, on the mountains. Some weeks previous to this fine eclipse, when I informed the Spaniards of the belt along which it could be observed, I had invited them to note all the interesting phenomena they might witness, including the effects produced by the eclipse upon animals. Birds returned hurriedly to their nests, swallows lost themselves, sheep huddled into compact packs, partridges were hypnotized, frogs croaked as if it were night, fowls took refuge in the hen-house, and cocks crowed, bats came out, and were surprised by the sun, chicks gathered under their mothers' wing, cage-birds ceased their songs, some dogs howled, others crept shivering to their masters' feet, ants returned to the antheap, grasshoppers chirped as at sunset, pigeons sank to the ground, a swarm of bees went silently back to their hive, and so on. These creatures behaved as though the night had come, but there were also signs of fear, surprise, even of terror, differing only "in degree" from those [Pg 285]manifested during the grandiose phenomenon of a total eclipse by human beings unenlightened by a scientific education. At Madrid the eclipse was only partial. The young King of Spain, Alfonso XIII, took care to photograph it, and I offer the photograph to my readers (Fig. 79), as this amiable sovereign did me the honor to give it me a few days after the eclipse. Fig. 79.—The Eclipse of May 28, 1900, as photographed by King Alfonso XIII, at Madrid. The technical results of these observations of solar eclipses relate more especially to the elucidation of the grand problem of the physical constitution of the Sun. We alluded to them in the chapter devoted to this orb. The last great total eclipses have been of immense value to science. The eclipses of the Moon are less important, less interesting, than the eclipses of the Sun. Yet their aspect must not be neglected on this account, and it may be said to vary for each eclipse. [Pg 286] Generally speaking, our satellite does not disappear entirely in the Earth's cone of shadow; the solar rays are refracted round our globe by our atmosphere, and curving inward, illumine the lunar globe with a rosy tint that reminds one of the sunset. Sometimes, indeed, this refraction does not occur, owing doubtless to lack of transparency in the atmosphere, and the Moon becomes invisible. This happened recently, on April 11, 1903. For any spot, eclipses of the Moon are incomparably more frequent than eclipses of the Sun, because the cone of lunar shadow that produces the solar eclipses is not very broad at its contact with the surface of the globe (10, 20, 30, 50, 100 kilometers, according to the distance of the Moon), whereas all the countries of the Earth for which the Moon is above the horizon at the hour of the lunar eclipse are able to see it. It is at all times a remarkable spectacle that uplifts our thoughts to the Heavens, and I strongly advise my readers on no account to forego it. [Pg 287]