What a charming picture to impress upon the sky!
But now in the twentieth century we analyze this dust which the ancients claim their Perseus raised—and what do we find? Every particle in that misty path is a mighty sun, suspended amidst multitudes of other mighty suns, massed in one long strip of splendor across the sky. For (calmly speaking) the Milky Way is a zone of innumerable stars so very distant that the individual lights are blended in one continuous band of silvery haze.
Against this glorious path stands Perseus, sword upraised among its stars, while entangled in the fearful locks of the Gorgon Medusa glows Algol, the "Blinking Demon." This so-called demon-star actually winks, that is, it indulges in one long, slow wink at intervals of exactly 2 days, 20 hours and 49 minutes. Such a phenomenon used to be a source of terror to the Arabs who feared it might be predictive of some disaster.
Although Perseus and the Gorgon are figments of fancy the wink of this amazing star is not imaginary by any means, for its light actually drops from the 2nd magnitude to the 4th magnitude and stays thus, half darkened, for about 20 minutes. Then it begins to slowly brighten and in the course of the next three hours regains its former brilliancy. In the clear air of the desert where the large stars burn like fire-brands, this change in brightness is very noticeable. Since it was not understood, it seemed terrifying and the superstitious Arabs imagined it to be the eye of a demon. It seemed a fitting star for the ancient Greeks to place on the grewsome head of the Gorgon Medusa where ever after it has flashed and faded in the most eerie fashion.
The mystery of this winking star was not discovered until 1889. Then Vogel found that the periodical change of brightness in Algol is caused by a huge dimly lighted sun,—relatively dark compared with Algol,—which revolves around the major sun at a distance of only 3,000,000 miles. (The earth revolves at a distance of 93,000,000 miles from our sun.) Every time this darker body passes between Algol and the earth, five-sixths of the light from Algol is cut off, thus making it appear to blink. Vogel also found, through the aid of the spectroscope, the diameter and mass of these stars. Algol was found to be about one million miles in diameter with a mass less than half that of the sun while its companion was found to be about 800,000 miles in diameter with a mass about one fourth that of our sun.
Thirty stars are now known to be of the Algol type. One of the most remarkable of these, V. Puppis, was found to be in the southern hemisphere and was carefully examined by Dr. A. W. Roberts. This star has a light variation of only 1½ days and is believed to whirl so closely to its companion that it is in actual contact.
The most favorable seasons for seeing Algol during the early evening are in the autumn, winter and early spring; in the autumn, low in the northeast, when it rises at sunset in the middle of September; in the winter, high up in the north, not far from the zenith; and in the spring, low down in the northwest. At the correct time it is possible for anyone to see its change in brilliancy although the best time to watch for this is during September and October. Algol rises at sunset in the middle of September and consumes 9 hours and 12 minutes in reaching the meridian. To best appreciate the change in this star compare it with the stars near by, especially to the 4th magnitude star that lies quite near to it.
Thus Perseus holds Algol on the Gorgon's head which flashes with "fiery snakes,"—his right hand brandishes a glittering sword, his armor is decked with stars, while the 'dust' he raised swirls in a milky path from the zenith to the trees on the horizon.
In the Sword Hand of Perseus the ancient Greeks saw the gleam of the sword borrowed from Mercury, a diamond-bladed, diamond-hilted sword, carved from a single diamond, but modern astronomers searching in the same spot discovered a more wonderful object for, through the eye of a telescope, the two nebulous patches of hazy light on the Sword Hand were resolved into countless stars! These star clusters are interesting even in a field-glass although higher powers disclose them as veritable sun-bursts of diamond-like stars. The two clusters may be located about half-way between Mirfak, the brightest star in the Segment of Perseus, and the "W" of Cassiopeia.
One might at first glance take these crowded masses of stars as an example where the great force of gravity had worked not wisely but too well; but it is only the unbelievable distance that our earth lies from these stars which makes them look so closely clustered together. Would the brighter naked-eye stars which bespangle our sky look like this—a glimmering spot—from so vast a distance? To know that our solar cluster of stars is not the only cluster in the heavens is enough to take a little of the conceit out of man's colossal opinion of himself.