Several estimates have been made which agree well together; whether direct use is made of known parallaxes, or comparison is made with binaries of well-determined orbits of the same spectral type as the sun, in which therefore it may be assumed there is the same relation between mass and brilliancy (Gore), the result is found that the sun's magnitude is - 26.5, or the sun is Io n times as brilliant as a first magnitude star; it would follow that the sun viewed from a Centauri would appear as of magnitude 0.7, and from a star of average distance which has a parallax certainly less than o 1 ", it would be at least fainter than the fifth magnitude, or, say, upon the border-line for naked-eye visibility.
There is a very striking relation between the eccentricity and the period of a system; in general the binaries of longest period have the greatest eccentricities.
The relation applies not only to the visual but to the spectroscopic binaries; these, having shorter periods than the visual binaries, have generally quite small eccentricities.
Up to 1905, 140 spectroscopic binaries had been discovered; a list of these is given in the Lick Observatory Bulletin, no.
A continuous gradation can be traced from the most widely separated visual binaries, whose periods are many thousand years, to spectroscopic binaries, Algol and # Lyrae variables, whose periods are a few hours and whose components may even be in contact, and from these to dumb-bell shaped stars and finally to ordinary single stars.