The Hero of the Night Sky

Hercules, known for the legendary Greek hero, is a constellation located in the Northern Hemisphere. As the fifth-largest of the 88 modern constellations, it spans a significant area of the night sky. The constellation is rich in deep sky objects and is home to one of the brightest globular clusters in the Northern Hemisphere.

Historical Overview

Hercules is one of the oldest constellations, with roots in ancient Babylon and Greece. To the ancient Greeks, this constellation represented Hercules, the demigod known for his strength and his twelve labors. Ptolemy, the Greco-Roman astronomer, listed it among his 48 constellations in the 2nd century. Despite its ancient origins, the constellation's shape doesn't resemble the hero and is often depicted as a man kneeling or a man wearing a cloak.

Location and Main Features

Hercules is located in the fourth quadrant of the Northern Hemisphere (NQ4) and can be seen at latitudes between +90? and -50?. It is bordered by constellations such as Draco, Bootes, Corona Borealis, Serpens Caput, Ophiuchus, Aquila, Sagitta, and Lyra. It spans 1225 square degrees, making it one of the larger constellations in the night sky.

Major Stars

Despite its large size, Hercules does not have any exceptionally bright stars. The brightest star, Alpha Herculis or Rasalgethi, is a red giant variable star with an apparent magnitude that varies from 3.1 to 3.9. The star's name comes from the Arabic phrase meaning "the kneeler's head," referring to the constellation's depiction as a kneeling man.

Beta Herculis or Kornephoros, meaning "club-bearer" in Greek, is another significant star. It's a yellow giant with a magnitude of 2.81, making it nearly as bright as Alpha Herculis. Gamma Herculis and Delta Herculis are other notable stars, both of them being binary star systems.

Deep Sky Objects

Hercules is home to several deep-sky objects, the most famous of which is M13 or the Hercules Globular Cluster. This is one of the brightest globular clusters in the Northern Hemisphere and can be seen with the naked eye under good conditions. The cluster contains hundreds of thousands of stars and is about 25,000 light-years away.

In addition to M13, Hercules houses another globular cluster, M92, which is often overshadowed by the larger M13 but is a worthy target for amateur astronomers. Several galaxies also reside within the boundaries of Hercules, including NGC 6210 and Abell 2151 (the Hercules Cluster of galaxies).

Observation

Hercules reaches its highest point in the sky during the months of July and August, making these the best months for observation. In mid-northern latitudes, Hercules is visible in the evening from late spring through the summer and into early fall. The "Keystone" asterism, a quadrilateral formed by the stars Epsilon, Zeta, Eta, and Pi Herculis, can serve as a guide to finding the constellation and its deep-sky objects.

Hercules in Modern Astronomy

Today, Hercules serves as an important navigation aid for astronomers and is a popular target for amateur astronomers due to its prominent globular clusters and galaxies. Moreover, the search for exoplanets has revealed several within the constellation, adding another dimension to our understanding of this vast celestial expanse.

* Constellation shown for northen hemisphere skies. For the southern hemisphere, constellations appear rotated 180 degrees (upside-down and left-right reversed) from what is shown. Remember that seasons are reversed too - summer in northern latitudes is winter in southern latitudes.

** Circumpolar constellations are visible year-round in the hemisphere listed (and not at all in the opposite hemisphere).