M45

Undoubtedly the most famous galactic cluster in the heavens: the Pleiades have been known since remote antiquity, almost 1,000 years BC. Hesiod referred to their disappearance behind the Sun for 40 days in the summer: Their heliacal rising (i. e. the first appearance in the morning sky, before the rising of the Sun), was an remarkable astronomical event in the ancient world: was the sign of the opening of the navigational season in the Mediterranean world, and Julius Caesar made to begin his calendar from this day. Homer mentions them in the fifth book of the Odissea and there are several references to the Pleiads also in the Bible: in the Book of Job and in Amos, (Minor prophets, two times).

The Pleiads were known in the history like the "seven sisters" or like the "seven virgins", and are generally taken to be the seven daughters from Atlantas and Pleione: Alcyone, Asterope, Celaeno, Electra, Maia, Merope and Taygeta; they were also half-sisters of the Hyades. According to a version of the myth, these very handsome nymphs had pursued by the hunter Orion through the woods of the Boeotia for five years, until Zeus transferred them all, included Orion's dog, between the stars.

The Greek myth of the Lost Pleiad is due to the poor visibility of the seventh star; but, strangely, there are almost three versions of the myth: the most widespread version identifies her as Electra, who is said to have veiled her face in shame at having married a mortal, the King of Corinth, while all her sisters had been wedded to gods. The story of the Lost Pleiad, nevertheless, is not confined to the Greek world: a similar tradition appears also in Japan, in the legends of Australian aborigines, in Gold Coast of Africa, in Borneo.

There seems superfluous give indications for find the Pleiads. Between all the objects of the Catalogue, no other is so known and showy. At least 6 members of the cluster are easily visible to naked eye; under very good conditions this number increase to 9, and, under a clear sky and dark jumps straight beyond the dozen. Carmelo Zannelli, author of best part of the photos that illustrates this site, sees 11 of it.

Visually, the nine brightest stars are concentrated in a field slightly over 1° in diameter. A good pair of inoculars gives a vision of it of together enthusiastically, while a telescope, also small, doesn't succeed to embrace all the cluster, unless anunusually low magnification is used (the nine brighter stars are contained in a field of little more than 1° of diameter).
If you want to perceive the weak nebulosity surrounding the brightest stars, you need openings rather elevated: a good rich field telescope and a very dark sky. The present author, neverthless, likes most the 11x70 binoculars, but even a 7x50 gives a superb sight.

They don't need big means, instead, for the photo. With a film from 800 ISO and focal ratio around f/4, in ten or fifteen minutes is possible begin to reveal traces of the nebulosity (obviously, with a system of pursuit, as more accurate as longer it is the focal that employee).

It is a very young cluster, perhaps 20 million of years (Baade): it doesn't contain any red giant, but Cecilia Payne-Gaposhkin affirms that in M45 there is any white dwarfs. The cluster contains 300 to 500 stars in a sphere of about 50 light-years diameter, surrounding by a faint reflection nebula.

The recent observations in the 1995 revealed several objects, candidates to be classified in a particularly interesting type of stellar bodies: the so-called brown dwarfs.

Alcyone (h Tauri) is the brighter star than the group. It is brighter around 1,000 times than the Sun, and bigger, probably, almost 10 times. All the brighter stars are in rapid rotation; Pleione is one of the most rapidly rotating stars known. This star is also a variable, ranging from 4.77 to 5.5 mag.