Homer, the "Odyssey":
'Ulysses sat at the helm and never slept, keeping his eyes upon the Pleiades.....'
Charles Messier(March 4th, 1769):
'A cluster of stars, known by the name of the Pleiades.'
'Nebula seen in a 2-inch telescope, but invisible in an 11-inch.'
from Tennyson's poem (1837) Locksley Hall:
'Many a night I saw the Pleiads,
rising thro' the mellow shade,
Glitter like a swarm of fire-flies tangled in a silver braid.'.
The Pleiades have been known since ancient times. They were mentioned by Homer about 750 B.C., by biblical Amos about 750 B.C., and by Hesiod about 700 B.C. At least 6 member stars are visible to the unaided eye, while under excellent conditions this 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 had correctly drawn 11 Pleiades stars, while Kepler quotes observations of up to 14. The Pleiades is also known as "The Seven Sisters", based on an ancient Greek myth, where the stars of the cluster are the seven daughters of Atlas and Pleione: Alcyone, Asterope, Celaeno, Electra, Maia, Merope, and Taygeta, all half-sisters of the Hyades. According to the myth the sisters were pursued thru the woods by the hunter Orion for five years until an angry Zeus placed all of them, including Orion's dog (Canis Major) in the night sky.
M-45 is a relatively young open star cluster consisting of at least 500 member stars. The current age estimate is about the cluster is about 100,000 years old. The brightest member stars are all rapidly rotating hot blue giants. There is recent evidence of a dust disk around one of the dimmer members, which may mean that there are planets being formed in the cluster.
Reflection Nebula: The Pleiades appear to be surrounded by intricate blue filaments of light. This nebulosity is the result of starlight scattering (reflecting) off minute grains of interstellar dust in the vicinity. The dust particles are inside a cloud of mostly hydrogen gas that the cluster seems to be plowing into. This is believed to be a random circumstance, and that the dust in the reflection nebula is not the remains of the gas cloud that M-45 formed from. Some of the brightest strands loop around the bright member star Merope (the Merope Nebula, or NGC 1435).
The Distance Controversy: The distance to the Pleiades is of major importance to modern astronomy because it is one of the major facts needed for our understanding of the distance to most other objects. For many years various studies indicated a distance of about 440 light years. However, data from the Hipparcos satellite, designed to give the best estimates available for near star distances, came up with a distance of about 330 light years. Many astronomers were dismayed and believed that the Hipparcos estimate was too small. More recent estimates by the Hubble Space Telescope (and other instruments) have agreed with the older 440 light year figure. The Hipparcos team has issued a revised distance based on a new analysis of their data that is 399 +/- 6, light years. Astronomers are currently locked in a major battle over the interpretation of the data from the various instruments. A new, more accurate distance determining satellite is projected for launch soon. (Refer to the following Sky & Telescope news item.).
George Normandin, KAS
November 25th, 2007