Hercules (constellation) (original) (raw)

Hercules (abreviation: Her), representing the mythical hero famed for his 12 labors, is a very large but unspectacular northern constellation. It contains the Keystone asterism, named after its shape, which is made by four of the main stars in Hercules – Epsilon, Zeta (Ruticulus), Eta, and Pi Her. See below for details of the constellation's brightest stars and interesting deep sky objects.

Hercules Cluster

Figure 2. The Hercules Cluster.

The Hercules Cluster (Abell 2151) is a loose unsymmetrical cluster of about 75 bright galaxies, some 500 million light-years away and about 6 million light-years across (Figure 2). It contains an unusually high proportion of spiral galaxies and also galaxies that shown evidence of interaction or other peculiar features (see galaxy interaction).

Hercules X-1

Hercules X-1 is an X-ray pulsar that is a member of an eclipsing binary system with an orbital period of 1.7 days (Figure 3); it lies about 15,000 light-years away. The visible component has been identified as the blue variable HZ Herculis, whose spectrum varies from late A or early F to B. Her X-l has a pulsation period of 1.2378 seconds, presumed to be its rotation period, and shows a 35-day quasi-periodicity in the X-ray region (but not in the optical). It is thought to move in a nearly circular orbit, to be accreting matter from HZ Her, and to have a mass of about 0.7 solar mass. The orbital period is stable, but the pulsation period is speeding up at a rate of about 1 part in 100,000 per year. The X-ray eclipse lasts 0.24 days.