Eta

Its story

Eta Herculis marks one corner of the keystone trapezium that forms the body of the hero in the summer sky. A yellow giant, broader and older than the Sun, it lies just over a hundred light-years away. Its warm light, having travelled since Napoleonic times, traces one of four points the ancients called the Falling Keystone, since it tips toward the zenith on the shortest nights of the year.