Constellation for July 2023 –
Hercules
Hercules is an ancient constellation representing the mythological hero who completed the twelve labours, including killing the Nemean lion with his bare hands (hence the nearby constellation Leo). Hercules lies between two bright stars: Arcturus to the south-east, and Vega to the north-west. It should be an easily identified constellation, but is hard to make out in the summer sky because of its relatively faint stars. It only has two fairly bright stars and even its famous “Keystone” asterism is difficult to see in Havering.
On the edge of the Keystone is the Great Hercules Cluster [1], Messier 13, a bright globular cluster which is easily made out in binoculars. The dimmer but still impressive globular cluster Messier 92 [2] lies above the Keystone (in the Keystone image at the top of this page, going clockwise from the bright orange star at the top left - Pi Herculis - the other “stars” are Eta Herculis, Messier 13, Zeta Herculis and Epsilon Herculis).
There are several nice doubles in Hercules. Rasalgethi (Alpha Herculis) lies well below the Keystone on the boundary with Ophiuchus, and is not actually the brightest star in Hercules. It is a close double with two fairly bright stars which are yellow and blue. You will probably have to use a high magnification to split it.
95 Herculis [3] is closer to the Keystone and is a slightly wider pair of two yellow stars.
Marsic
[4] (Kappa Herculis) is a fairly wide double with a yellow primary and a secondary which can be seen by different observers as a variety of colours ranging from orange to blue. It lies close to the boundary between Hercules and Serpens Caput. Marsic used to be called Marfik, but the IAU recently renamed it Marsic as there is another Marfik (Lambda Ophiuchi); it is incorrectly listed in Celestron handsets (under double stars) as Maasym (actually Lambda Herculis).
