In δ we have a very wide and easy double; magnitudes three and a half and eight and a half, distance 110", p. 75°. The smaller star has a lilac hue. We can not hope with any of our instruments to see all of the three stars contained in μ, but two of them are easily seen; magnitudes four and seven, distance 108", p. 172°. The smaller star is again double; magnitudes seven and eight, distance 0.77", p. 88°. It is clearly a binary, with a long period. A six-inch telescope that could separate this star at present would be indeed a treasure. Σ 1926 is another object rather beyond our powers, on account of the contrast of magnitudes. These are six and eight and a half; distance 1.3", p. 256°.
Other doubles are: 44 (Σ 1909), magnitudes five and six, distance 4.8", p. 240°; 39 (Σ 1890), magnitudes both nearly six, distance 3.6", p. 45°. Smaller star light red; ι, magnitudes four and a half and seven and a half, distance 38", p. 33°; κ, magnitudes five and a half and eight, distance 12.7", p. 238°. Some observers see a greenish tinge in the light of the larger star, the smaller one being blue.
There are one or two interesting things to be seen in that part of Canes Venatici which is represented on [map No. 11]. The first of these is the star cluster 3936. This will reward a good look with the five-inch. With large telescopes as many as one thousand stars have been discerned packed within its globular outlines.
The star 25 (Σ 1768) is a close binary with a period estimated at one hundred and twenty-five years. The magnitudes are six and seven or eight, distance about 1", p. 137°. We may try for this with the five-inch, and if we do not succeed in separating the stars we may hope to do so some time, for the distance between them is increasing.
Although the nebula 3572 is a very wonderful object, we shall leave it for another evening.
Eastward from Boötes shines the circlet of Corona Borealis, whose form is so strikingly marked out by the stars that the most careless eye perceives it at once. Although a very small constellation, it abounds with interesting objects. We begin our attack with the five-inch on Σ 1932, but not too confident that we shall come off victors, for this binary has been slowly closing for many years. The magnitudes are six and a half and seven, distance 0.84", p. 150°. Not far distant is another binary, at present beyond our powers, η. Here the magnitudes are both six, distance 0.65", p. 3°. Hall assigns a period of forty years to this star.
The assemblage of close binaries in this neighborhood is very curious. Only a few degrees away we find one that is still more remarkable, the star γ. What has previously been said about 42 Comæ Berenicis applies in a measure to this star also. It, too, has a comparatively small orbit, and its components are never seen widely separated. In 1826 their distance was 0.7"; in 1880 they could not be split; in 1891 the distance had increased to 0.36", and in 1894 it had become 0.53", p. 123°. But in 1899 Lewis made the distance only 0.43". The period has been estimated at one hundred years.
While the group of double stars in the southern part of Corona Borealis consists, as we have seen, of remarkably close binaries, another group in the northern part of the same constellation comprises stars that are easily separated. Let us first try ζ. The powers of the three-inch are amply sufficient in this case. The magnitudes are four and five, distance 6.3", p. 300°. Colors, white or bluish-white and blue or green.
Next take σ, whose magnitudes are five and six, distance 4", p. 206°. With the five-inch we may look for a second companion of the tenth magnitude, distance 54", p. 88°. It is thought highly probable that σ is a binary, but its period has simply been guessed at.
Finally, we come to ν, which consists of two very widely separated stars, ν1 and ν2, each of which has a faint companion. With the five-inch we may be able to see the companion of ν2, the more southerly of the pair. The magnitude of the companion is variously given as tenth and twelfth, distance 137", p. 18°.