γ Leonis. This double star was for many years considered to be a binary, but Burnham has shown that all the measures may be satisfactorily represented by a straight line, and that consequently the pair merely forms an “optical double.”
42 Comæ Berenices. This is a binary star of which the orbit plane passes nearly through the earth. The period is about 25½ years, and Burnham says the orbit “is as accurately known as that of any known binary.”
σ Coronæ Borealis. Burnham says that the orbits hitherto computed—with periods ranging from 195 years (Jacob) to 846 years (Doberck) are “mere guess work,” and it will require the measures of at least another century, and perhaps a much longer time, to give an approximate period (Cat., p. 209). So here is some work left for posterity to do in this field.
70 Ophiuchi. With reference to this well-known binary star, Burnham says, “the elements of the orbit are very accurately known.” The periods computed range from 86·66 years (Doolittle) to 98·15 years (Powell). The present writer found a period of 87·84 years, which cannot be far from the truth. Burnham found 87·75 years (Cat., p. 774). In this case there is not much left for posterity to accomplish.
61 Cygni. With reference to this famous star Burnham says, “So far the relative motion is practically rectilinear. If the companion is moving in a curved path, it will require the measures of at least another half-century to make this certain. The deviation of the measured positions during the last 70 years from a right line are less than the average errors of the observations.”
Burnham once saw a faint companion to Sirius of the 16th magnitude, and measured its position with reference to the bright star (280°·6: 40″·25: 1899·86). But he afterwards found that it was “not a real object but a reflection from Sirius” (in the eye-piece). Such false images are called “ghosts.”
With reference to the well-known double (or rather quadruple) star ε Lyræ, near Vega, and supposed faint stars near it, Burnham says, “From time to time various small stars in the vicinity have been mapped, and much time wasted in looking for and speculating about objects which only exist in the imagination of the observer.” He believes that many of these faint stars, supposed to have been seen by various observers, are merely “ghosts produced by reflection.”
The binary star ζ Boötis, which has long been suspected of small and irregular variation of light, showed remarkable spectral changes in the year 1905,[319] somewhat similar to those of a nova, or temporary star. It is curious that such changes should occur in a star having an ordinary Sirian type of spectrum!
A curious quadruple system has been discovered by Mr. R. T. A. Innes in the southern hemisphere. The star κ Toucani is a binary star with components of magnitudes 5 and 7·7, and a period of revolution of perhaps about 1000 years. Within 6′ of this pair is another star (Lacaille 353), which is also a binary, with a period of perhaps 72 years. Both pairs have the same proper motion through space, and evidently form a vast quadruple system; for which Mr. Innes finds a possible period of 300,000 years.[320]
It is a curious fact that the performance of a really good refracting telescope actually exceeds what theory would indicate! at least so far as double stars are concerned. For example, the famous double-star observer Dawes found that the distance between the components of a double star which can just be divided, is found by dividing 4″·56 by the aperture of the object-glass in inches. Now theory gives 5″·52 divided by the aperture. “The actual telescope—if a really good one—thus exceeds its theoretical requirements. The difference between theory and practice in this case seems to be due to the fact that in the ‘spurious’ star disc shown by good telescopes, the illumination at the edges of the star disc is very feeble, so that its full size is not seen except in the case of a very bright star.”[321]