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Page:Popular Science Monthly Volume 32.djvu/69

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which a quarter of a century later made the name of Sir William Herschel world-renowned. The planet Uranus passed near Delta in 1756, and Tobias Mayer saw it, but it moved so slowly that he took it for a fixed star, never suspecting that his eyes had rested upon a member of the solar system whose existence was, up to that time, unknown to the inhabitants of Adam's planet.

Above Aquarius you will find the constellation Pegasus. It is conspicuously marked by four stars of about the second magnitude, which shine at the corners of a large square, called the Great Square of Pegasus. This figure is some fifteen degrees square, and at once attracts the eye, there being few stars visible within the quadrilateral, and no large ones in the immediate neighborhood to distract attention from it. One of the four stars, however, as will be seen by consulting Map 2, does not belong to Pegasus, but to the constellation Andromeda. Mythologically, this constellation represents the celebrated winged horse of antiquity:

"Now heaven his further wandering flight confines,
Where, splendid with his numerous stars, he shines."

The star Alpha (α) is called Markab; Beta (β) is Scheat, and Gamma (γ) is Algenib; the fourth star in the square, belonging to Andromeda, is called Alpheratz, Although Pegasus presents a striking appearance to the unassisted eye, on account of its great square, it contains little to attract the observer with an opera-glass. It will prove interesting, however, to sweep with the glass carefully over the space within the square, which is comparatively barren to the naked eye, but in which many small stars will be revealed, of whose existence the naked-eye observer would be unaware. The star marked Pi (π) is an interesting double, which can be separated by a good eye without artificial aid, and which, with an opera-glass, presents a fine appearance.

And now we come to our third little map, representing the constellations Cetus, Pisces, Aries, and the Triangles. In consulting it the observer is supposed to face the southeast. Cetus is a very large constellation, and from the peculiar conformation of its principal stars it can be readily recognized. The head is to the east, the star Alpha (α), called Menkar, being in the nose of this imaginary monster of the sky-depths. This constellation is supposed to represent the monster that was sent, according to the fable, by Neptune to devour the fair Andromeda, but whose bloodthirsty design was happily and gallantly frustrated by Perseus, as we shall learn from starry mythology farther on.

By far the most interesting object in Cetus is the star Mira, marked Omicron (ο) in the map. This is a famous variable star—a sun that sometimes shines a thousand times more brilliantly than at others! It changes from the second magnitude to the ninth or tenth, its period