Page:Popular Science Monthly Volume 46.djvu/767

Rh sun about 375,000 times in volume, and that its diameter is no less than 62,350,000 miles! Imagine the earth and the other planets constituting the solar system removed to Arcturus and set revolving around it in orbits of the same forms and sizes as those in which they circle about the sun. Poor Mercury! For that little planet it would indeed be a jump from the frying pan into the fire, because, as it rushed to perihelion. Mercury would plunge more than 2,500,000 miles beneath the surface of the giant star. Venus and the earth would perhaps melt like snowflakes at the mouth of a furnace. Even far-away Neptune, the remotest member of the system, would be bathed in torrid heat.

But stop! Look at the sky. Observe how small and motionless the disks of the stars have become. Back to the telescopes at once, for this is a token that the atmosphere is steady, and that "good seeing" may be expected. It is fortunate, for we have some delicate work before us. The very first double star we try in Boötes, Σ 1772, requires the use of the four-inch, and the five-inch shows it more satisfactorily. The magnitudes are sixth and ninth, distance 5″; p. 140°. On the other side of Arcturus we find ζ, a star that we should have had no great difficulty in separating thirty years ago, but which has now closed up beyond the reach even of our five-inch. The magnitudes are both fourth, and the distance about 0·5″, p. 285°. It is apparently a binary, and if so will some time widen again, but its period is unknown. The star 279, also known as Σ 1910, near the southeastern edge of the constellation, is a pretty double, each component being of the seventh magnitude; distance 4″; p. 212°. Just above ζ we come upon π, an easy double for the three-inch, magnitudes fourth and sixth; distance 6″; p. 99°. Next is ξ, a yellow and purple pair, whose magnitudes are respectively fifth and seventh; distance. less than 3″; p. 231°. This is undoubtedly a binary with a period of revolution of about a hundred and thirty years. Its distance decreased about 1″ between 1881 and 1891. It was still decreasing in 1894, when it had become 2·9″. The orbital swing is also very apparent in the change of the position angle.

The telescopic gem of Boötes, and one of "the flowers of the sky," is ε, also known as Mirac. When well seen, as we shall see it to-night, ε Boötis is superb. The magnitudes of its two component stars are two and a half (according to Hall, three) and six. The distance is about 2·8″, p. 326°. The contrast of colors—bright orange yellow, matched with brilliant emerald green—is magnificent. There are very few doubles that can be compared with it in this respect. The three-inch will separate it, but the five-inch enables us best to enjoy its beauty. It appears to be a binary, but the motion is very slow, and nothing certain is yet known of its period.