Star cluster No. 4440 is a striking object, its stars ranging from the ninth down to the twelfth magnitude.
Just north of Aquila is the little constellation Sagitta, containing several interesting doubles and many fine star fields, which may be discovered by sweeping over it with a low-power eyepiece. The star ζ is double, magnitudes five and nine, distance 8.6", p. 312°. The larger star is itself double, but far too close to be split, except with very large telescopes. In θ we find three components of magnitudes seven, nine, and eight respectively, distances 11.4", p. 327°, and 70", p. 227°. A wide double is ε, magnitudes six and eight, distance 92", p. 81°. Nebula No. 4572 is planetary.
Turning to Delphinus, we find a very beautiful double in γ, magnitudes four and five, distance 11", p. 273°, colors golden and emerald. The leader α, which is not as bright as its neighbor β, and which is believed to be irregularly variable, is of magnitude four, and has a companion of nine and a half magnitude at the distance 35", p. 278°. At a similar distance, 35", p. 335°, β has an eleventh-magnitude companion, and the main star is also double, but excessively close, and much beyond our reach. It is believed to be a swiftly moving binary, whose stars are never separated widely enough to be distinguished with common telescopes.
CHAPTER VI
FROM LYRA TO ERIDANUS
"This Orpheus struck when with his wondrous song
He charmed the woods and drew the rocks along."—Manilius.
We resume our celestial explorations with the little constellation Lyra, whose chief star, Vega (α), has a very good claim to be regarded as the most beautiful in the sky. The position of this remarkable star is indicated in [map No. 17]. Every eye not insensitive to delicate shades of color perceives at once that Vega is not white, but blue-white. When the telescope is turned upon the star the color brightens splendidly. Indeed, some glasses decidedly exaggerate the blueness of Vega, but the effect is so beautiful that one can easily forgive the optical imperfection which produces it. With our four-inch we look for the well-known companion of Vega, a tenth-magnitude star, also of a blue color deeper than the hue of its great neighbor. The distance is 50", p. 158°. Under the most favorable circumstances it might be glimpsed with the three-inch, but, upon the whole, I should regard it as too severe a test for so small an aperture.
Vega is one of those stars which evidently are not only enormously larger than the sun (one estimate makes the ratio in this case nine hundred to one), but whose physical condition, as far as the spectroscope reveals it, is very different from that of our ruling orb. Like Sirius, Vega displays the lines of hydrogen most conspicuously, and it is probably a much hotter as well as a much more voluminous body than the sun.