Hercules is an ancient constellation depicting a kneeling man and has been known under several names since Babylonian times. The striking square from the stars η, ζ, ε and π, which depicts his body, is also called Keystone.
α Herculi is the brightest star of Hercules. It bears the name Ras Algethi, which probably goes back to the Arab Ras Al Jathiyy and means the “head of the kneeling“ – so, Hercules is upside-down in the sky. Ras Algethi is a red supergiant star whose brightness varies within a period of about 90 days between 3.1 to 3.9m – not too impressive. Its diameter is about 600 solar diameters. Ras Algethi is together with Mira (ο Ceti) and Betelgeuse (α Orionis) one of the largest and coolest known stars in the sky. If it stood in the place of our Sun, it would extend far into the asteroid belt. Nevertheless, it has only a few solar masses. The 380 light-years distant star also has a close companion, but this star is only visible in a telescope.
M 13 is the largest and most impressive globular cluster which is visible from the Northern Hemisphere. With a brightness of 5.9m, it can be seen under very good conditions even with the naked eye. In binoculars, M 13 appears as a starless nebula with a diameter of up to 23 minutes of arc, or about half as large as the full Moon. You need at least 20x magnification to resolve the first of its half a million stars. The globular cluster has a diameter of 160 light-years and is about 23,000 light-years away. Its distance from the center of the galaxy is similar to that of our Sun – about 30,000 light-years.