Eps

Its story

Epsilon Herculis is one of the four corners of the Keystone, the luminous trapezoid that defines the torso of Hercules in the northern summer sky. The faintest of the four, it is a white A0 star at 155 light-years, in fact a spectroscopic binary whose components reveal themselves only through the sway of their spectral lines. Without it, the celestial hero's geometry would collapse.