xi

The stars ξ and β Scorpii form triple systems in which the components are differently arranged.

To any point (x, y) of ƒ will then correspond a definite point (ξ, η) of F.

Its position seems to have determined its form, which is certainly that of X rather than of Ξ.

The star ξ has a companion, which forms a fine test for an opera-glass, and is well worth looking for.

Up near the end of the northern prolongation of the constellation we perceive the star ξ.