M 45
OPEN STAR CLUSTER

Right Ascension:
03h 47m 0s

Best Seen:
12/15-3/15

Declination:
24ยบ 07' 00"

Magnitude:
1.6

Computer File:
m45

Constellation:
Taurus

Actual

Compared to

Distance

380 l.y.

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Actual Brightness

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Number of stars

500

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Diameter

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Age

100 million years

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Integrated Spectral Type

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WHAT TO LOOK FOR THROUGH THE TELESCOPE:

  1. Recommended eyepiece: 80 mm, using 6".

  2. When people look through the telescope the cluster will appear as a group of individual stars; all seven primary stars should be visible in the field of view.

M45 INFORMATION:

  1. The Pleiades are among those objects which are known since pre-historical times. The first written record of the cluster dates to around 1000 B.C.

  2. The Pleiades is the most famous star cluster on the sky and can be seen without binoculars from even the depths of a light-polluted city. It is one of the brightest and closest open clusters.

  3. From the city, one can see six of the stars. With a clear, dark sky, the number jumps to 12.

  4. The cluster includes mostly faint stars, spread over a 2 degree field. (four times the diameter of the Moon.)

  5. This is a reflection nebulae, reflecting the light of the bright stars situated near or within them.

  6. The Pleiades have an expected future lifetime (as a cluster) of about 250 million years. After that, they will have been spread as individual (or multiple) stars along their orbital path.

  7. The Pleiades contain some white dwarf stars. These stars were once massive so that they evolved fast, but quickly lost the greatest part of their mass. Possibly they have lost another considerable percentage of their mass in the planetary nebula.

OPEN CLUSTER INFORMATION:

  1. They lie in the plane of the galaxy.

  2. They are made of young (newly formed) stars.

  3. They are believed to originate from large cosmic gas/dust clouds in the Milky Way.

  4. They will continue to orbit the galaxy through the disk.

  5. Most open clusters will probably dissipate after a few 100 million to a few billion years since they are only loosely bound by their mutual gravity.

  6. The separation of stars is about 3 light years. In the solar neighborhood stars are 4-5 light years apart.

  7. They contain a few hundred to a few thousand stars.

  8. Star clusters are important to astronomers because they are used to test ideas of stellar evolution. Astronomers are able to do this because all the stars in the cluster are assumed to have formed at the same time.

a. Theories of stellar evolution are based on computer models. The computer models are based on what we know about stars and the laws of physics. One of the things these models tell us is that different stars age at different rates.

b. To test their theories, astronomers generate models of stars that would be found in a cluster. They then compare the appearance of this model cluster with observations of a real cluster. If there are significant differences, the astronomers change the model until it matches the real cluster.

Other Pleiades information:

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

  2. Their Japanese name is "Subaru", which was taken to christen the car of same name.

  3. The Persian name is "Soraya", after which the former Iranian empress was named.

  4. Old European (English and German) names indicate they were once compared to a "Hen with Chicks".

  5. On March 4, 1769, Charles Messier included the Pleiades as number 45 in his first list of nebulae and star clusters, published 1771.

  6. The names of the brightest stars: Alcyone 2.90 Atlas 3.62 Electra 3.70 Maia 3.87 Merope 4.18 Taygeta 4.30 Celaeno 5.46 Asterope 5.80

  7. The Trumpler classification is given for the Pleiades as I,3, r, n.

  8. The cluster also contains several brown dwarfs.