Apastra

If we suppose the apastra of the two stars to occur simultaneously, there will be two minima, “but the maxima will be constant.”

But if both motions proceed in the same sense, then the binary stars will traverse that half of their galactic orbit with their apastra forward.

The rotation involved is that of the location of the peri- and apastra, i.e. the line of apsides of the ellipse: it is thus called apsidal motion.