Astronomical Curiosities: Facts and Fallacies
J. Ellard Gore
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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. 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.
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.” 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. 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.”
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 par