Starwatch: how to find Hercules and Corona Borealis

Two of the constellations first defined by Ptolemy, though faint, are well placed for observation this month

It is a good time of year to search out two of the fainter northern constellations. Once identified, both bring considerable pleasure because of their distinctive shapes. The first is Hercules, the hero, the body of which is often described as having the shape of a keystone. Although faint, it is quite easy to spot. Hercules was one of the constellations defined by the 2nd century astronomer Ptolemy, although it may have its origins in Babylonian astronomical tradition. The second constellation to look for is adjacent to the west. Corona Borealis, the northern crown, is a beautiful semi-circle of stars. It was also part of Ptolemy’s original list and represents the crown given to Ariadne by the god Dionysus. Perhaps the best way to locate these two constellations is to look for the bright white star Vega in the south east, and the bright orange star Arcturus in the south. A line drawn from Vega in Lyra to Arcturus in Boötes passes through Hercules and then through Corona Borealis.

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