To the right of Equuleus, towards the west-south-west is the constellation Delphinus. The upper left-hand star of the rhombus of stars forming the head of the Delphinus is the star [gamma] Delphini, a rather easy double (see Plate 5), the components being nearly 12” apart, their magnitudes 4 and 7, their colours golden yellow and flushed grey.
Turn we next to the charming double Albireo, on the beak of Cygnus, about 36 deg. above the horizon towards the west. The components are 34-1/2” apart, their magnitudes 3 and 6, their colours orange-yellow, and blue. It has been supposed (perhaps on insufficient evidence) that this star is merely an optical double. It must always be remembered that a certain proportion of stars (amongst those separated by so considerable a distance) must be optically combined only.
The star [chi] Cygni is a wide double (variable) star. The components are separated by nearly 26”, their magnitudes 5 and 9, their colours yellow and light blue. [chi] may be found by noticing that there is a cluster of small stars in the middle of the triangle formed by the stars [gamma], [delta], and [beta] Cygni (see Map 4, Frontispiece), and that [chi] is the nearest star of the cluster to [beta]. The star [phi] Cygni, which is just above and very close to [beta] (Albireo), does not belong to the cluster. [chi] is about half as far again from [phi] as [phi] from Albireo. But as [chi] descends to the 11th magnitude at its minimum the observer must not always expect to find it very easily. It has been known to be invisible at the epoch when it should have been most conspicuous. The period of this variable is 406 days.
The star 61 Cygni is an interesting one. So far as observation has yet extended, it would seem to be the nearest to us of all stars visible in the northern hemisphere. It is a fine double, the components nearly equal (5-1/2 and 6), both yellow, and nearly 19” apart. The period of this binary appears to be about 540 years. To find 61 Cygni note that [epsilon] and [delta] Cygni form the diameter of a semicircle divided into two quadrants by [alpha] Cygni (Arided). On this semicircle, on either side of [alpha], lie the stars [nu] and [alpha] Cygni, [nu] towards [epsilon]. Now a line from [alpha] to [nu] produced passes very near to 61 Cygni at a distance from [nu] somewhat greater than half the distance of [nu] from [alpha].
The star [mu] Cygni lies in a corner of the constellation, rather farther from [zeta] than [zeta] from [epsilon] Cygni. A line from [epsilon] to [zeta] produced meets [kappa] Pegasi, a fourth-magnitude star; and [mu] Cygni, a fifth-magnitude star, lies close above [kappa] Pegasi. The distance between the components is about 5-1/2”, their magnitudes 5 and 6, their colours white and pale blue.
The star [psi] Cygni may next be looked for, but for this a good map of Cygnus will be wanted, as [psi] is not pointed to by any well-marked stars. A line from [alpha], parallel to the line joining [gamma] and [delta], and about one-third longer than that line, would about mark the position of [psi] Cygni. The distance between the components of this double is about 3-1/2”, their magnitudes 5-1/2 and 8, their colours white and lilac.