« PreviousContinue »
can discern more than 4,000. This illusion may be
easily explained, when we remember how the impression of a bright light remains upon the retina, as in the whirling of a firebrand. However, the number
which may be seen with a telescope becomes altogether marvellous. Tn the cut is shown a portion
of the heavens where the naked eye sees but six stars. Could we examine the same region of the sky with more powerful instruments, new constellations would doubtless be descried in the infinite depths of space.
Scintillation.—The twinkling of the fixed stars is due to what is termed in Natural Philosophy "the interference of light." The air being unequally dense, warm, and moist in its various strata, transmits very irregularly the different colors of which white light is composed. Now one color prevails over the rest, and now another, so that the star appears to change color incessantly. As the purity of the air varies, the twinkling of the stars also changes, although it is always greatest near the horizon. Humboldt says that at Cumana, in South America, where the air is remarkably pure and uniform in density, the stars cease to twinkle after they have risen 15° above the horizon. This gives to the celestial vault a peculiarly calm and soft appearance.
Magnitude Of The Stars.—As the telescope reveals no disk of even the nearest stars, we know nothing of their comparative size. The finest spider's web, placed at the focus of the instrument, hides the star from the eye. When the moon passes in front of a star, the occultation is instantaneous, and not gradual, as in the case of the planets. Classification depends, therefore, upon their relative brightness. The most conspicuous are , termed stars of the first magnitude. There are about twenty of these. The number of second magnitude stars in the entire heavens is about sixty-five; of the third, about 200; of the fifth, 1,100; and of the sixth,
3,200. Few persons can see any smaller stars than those of the fifth or sixth magnitude. The ordinary telescope shows faint stars down to the tenth, while the more powerful instruments reveal those as low as the twentieth magnitude.
The Caube Of The Difference In The Brightness Of The Stars.—This may result from a difference in their distance, size, or intrinsic brightness. Whence it follows that the faintest stars may not be the most distant from the earth.
Names Of The Stars.—Many of the brightest stars received proper names at an early date; as Sirius, Arcturus. The stars of each constellation are distinguished by the letters of the Greek alphabet; the brightest being usually called Alpha, the next Beta etc.,—the name of the constellation, in the genitive case, being put after each. Ex., « Arietis, j8 Lyrse.*
* This means a of Aries, (3 of Lyra; the genitive case in Latin being equivalent to the preposition of.
When the Greek letters are exhausted, the Roman alphabet is used in the same way. Star catalogues are issued, containing the stars arranged in the order of their Right Ascension, and numbered for convenience of reference. Argelander's Charts have 300,000 stars marked in the northern hemisphere.
The Constellations.—From the earliest ages, the stars have been arranged in constellations, for the purpose of more readily distinguishing them. Some of these groups were named from their supposed resemblance to some figures, such as perching birds, pugnacious bulls, or contorted snakes, while others do honor to the memory of the classic heroes of antiquity.
"Thus monstrous forms, o'er heaven's nocturnal arch.
See Aries there Mb glittering bow unfold,
With a few exceptions, the likeness is purely fanciful. The heavens are much less of a menagerie than a celestial atlas would make them appear. The division into constellations is a mere relic of barbarism, entirely unworthy of modern civilization. Not only are the figures uncouth, and the origin often frivolous, but the boundaries are not distinct. Stars often occur under different names; while one constellation encroaches upon another. As Chambers well remarks, "Aries should not have a horn in Pisces and a leg in Cetus, nor should 13 Argos pass through the Unicorn's flank into the Little Dog. 51 Camelopardali might with propriety be extracted from the eye of Auriga, and the ribs of Aquarius released from 46 Capricorni." While, however, the constellations are thus rude and imperfect, there seems little hope of any change. Age gives them a dignity that insures their perpetuation.
Invention Of The Constellations.—This goes back into ages of which no record remains. By some it has been ascribed to the Greeks. When the signs of the zodiac were named, they doubtless coincided with the constellations. Aries (the ram) was so called because it rose with the sun in the springtime, and the Chaldean shepherds named it from