Friday, 21 March 2014


The beautiful Seven Sisters or Pleiades star cluster in the constellation of Taurus, complete with labels marking the main stars visible to the naked eye. Credit: Anglo-Australian Observatory/Royal Observatory, Edinburgh.


There are certain objects in the night sky that paradoxically and almost counter-intuitively appear much better with the naked eyes or with ordinary common or garden binoculars rather than expensive telescopes. One such object still visible in the early March evening sky after dusk that also defies even the most appalling city and urban light pollution is the Seven Sisters or Pleiades open star cluster. With a prominent place in ancient mythology, it's perhaps one of the most popular astronomical targets for the beginner... after all most youngsters are either taught about this beautiful cluster of stars at home or at school. Some may also be familiar with the constellation from its appearance on the badge on the bonnet of Japanese Subaru cars: the manufacturer was named after the constellation.

Infact, The Pleiades cluster, otherwise known as Messier 45 far from containing the six or seven stars seen with the unaided eye actually contains hundreds, with many more becoming visible through binoculars. For those in the northern hemisphere, the cluster is above and to the right of Orion the Hunter as one faces south in the constellation of Taurus the Bull.

Location of The Pleiades, M45. Look for the constellation of Orion the Hunter with his distinctive belt, and in the Northern Hemisphere, M45 is to the right and above.
The stars in the Pleiades are thought to have formed together around 100 million years ago, making them one fiftieth the age of our sun, and they are also close in astronomical terms to the Earth, they are just 425 light years away. They're very hot and hence blue in colour and indeed from a dark site strands and wisps of the star forming nebula of hydrogen gas from which the stars originated can still be seen.

The main stars have delightful names too emanating from Greek mythology, and being the seven daughters of Atlas and of Pleione, the daughter of Oceanus. Their names were Electra, Maia, Taygete, Alcyone, Celaeno, Sterope, and Merope. According to some versions of the myth, they committed suicide from grief at the fate of their father, Atlas, or at the death of their sisters, the Hyades. Other versions made them the attendants of Artemis, goddess of wildlife and of hunting, who were pursued by the giant hunter Orion, but were rescued by the gods and changed into doves. After their death, or metamorphosis, they were transformed into stars, but are still pursued across the sky by the constellation Orion to this day.

Finally, you may still be wondering why I recommended the naked eye or especially binoculars when looking at the Pleiades. The reason is quite simple: to gain the full effect of observing this beautiful 'open' star cluster you need to be able to see it all in the same field of view. The onus is on the word 'open', as M45 covers quite a large area of sky. The typical 4.5 or 5 degree field of view provided by 10x50 binoculars is just perfect. The limited field of view provided by a telescope is disappointing as you won't see the beauty of the group in its entirety. You will however see more stars of course, and from a dark site, possible nebulosity.


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