Open Cluster M45 , type 'c', in Taurus

Pleiades

[m45.jpg]
Right Ascension 03 : 47.0 (h:m)
Declination +24 : 07 (deg:m)
Distance 0.38 (kly)
Visual Brightness 1.6 (mag)
Apparent Dimension 110.0 (arc min)
Discovered by Known since
Ancient times

The Pleiades are among those objects which are known since the earliest times. At least 6 member stars are visible to the naked eye, while under moderate conditions this number increases to 9, and under clear dark skies jumps up to more than a dozen. (Vehrenberg, in his Atlas of Deep Sky Splendors, mentions that in 1579, well before the invention of the telescope, astronomer Moestlin has correctly drawn 11 Pleiades stars, while Kepler quotes observations of up to 14). According to Kenneth Glyn Jones, the earliest known reference of this cluster is a mention by Hesiod, about 1000 BC (according to Burnham, they were seen in connection to the agricultural seasons of that time). Homer mentions them in his Odyssee, and the Bible has three references to the Pleiades.

The Pleiades also carry the name "Seven Sisters"; according to Greek mythology, seven daughters and their parents. Their Japanese name is "Subaru", which was taken to christen the car of same name. Old European (e.g., English and German) names indicate they were once compared to a "Hen with Chicks".

Burnham points out that the name "Pleiades" may be derived from either the Greek word for "to sail", or the word "pleios" meaning "full" or "many". The name may be derived from the mythological mother, Pleione, which is also the name of one of the brighter stars.

According to Greek mythology, the main, visible stars are named for the seven daughters of "father" Atlas and "mother" Pleione: Alcyone, Asterope (a double star), Electra, Maia, Merope, Taygeta and Celaeno.

Modern observing methods have revealed that at least about 500 mostly faint stars belong to the Pleiades star cluster, spread over a 2 degree (four times the diameter of the Moon) field. Their density is pretty low, compared to other open clusters. This is one reason why the life expectation of the Pleiades cluster is also pretty low (see below).

Longer exposure photographs (and also short focal ratio, i.e. short focal length compared to their aperture, "rich field" telescopes of considerably good quality, especially good binoculars) have revealed that the Pleiades are apparently imbedded in nebulous material, obvious in our image, which was taken by David Malin with the UK Schmidt Telescope, and is copyrighted by the Royal Observatory Edinburgh and the Anglo-Australian Observatory.

Some believe the blue nebulosity is closer than the stars, and we just see their light through it.

The Pleiades nebulae are blue-colored, which indicates that they are reflection nebulae, reflecting the light of the bright stars situated near (or within) them.

The distance of the Pleiades cluster has been newly determined by direct parallax measures by ESA's astrometric satellite Hipparcos; according to these measurement, the Pleiades are at a distance of 380 light years (previously, a value of 408 light years had been assumed). The new value requires an explanation for the comparatively faint apparent magnitudes of the Pleiades stars.

As the Pleiades are situated close to the ecliptic (4 degrees off), occultation's of the cluster by the Moon occur quite frequently: This is a very appealing spectacle, especially for amateurs with less expensive equipment (actually, you can observe it with the naked eye, but even the smallest binoculars or telescopes will increase observing pleasure. Planets come close to the Pleiades cluster (Venus, Mars, and Mercury even occasionally pass through) to give a conspicuous spectacle.

Messier observed M45 the Pleiades on March 4th, 1769 "Star cluster known as the Pleiades.The position given is that of the star Alcyone." Charles Messier 

Close by: Aldebaran

Courtesy www.seds.org