Expert: Tom Whiting - 10/14/2006

Question
Tom, is it true to say the stars of the Pleiades are gravitationally bound whereas the stars of most of the constellations we have identified from Earth are generally not?
Is there a continuing mystery re the proximity to Earth (as established by the Hipparcos mission, for instance) versus the apparent brightness, of the Pleiades constellation, or has this since been adequately explained?
Have any reasonable suggestions arisen yet to account for the fact of so many distinct cultures, separated by geography and by time, apparently having independently derived the myth of the hunter (Orion) chasing 7 maidens, or six maidens and their mother (the Pleiades).
Does any further anomalous factor stand the Pleiades cluster apart from other constellations?  
Thanks

Answer
Hi Tony,
Well, first a definition is in order... a constellation is a defined area of the sky.....no inclusion of a man, animal, etc.  is now required.  Just like the states of the USA, they are simply defined areas of the sky as designated in 1930 by the IAU (International Astronomical Union) for location and identification purposes only, and there are 88 of
them, of which about 40 are visible from the N. Hemisphere.

Now the shocker to you because you seem to indicate
that the Pleiades is a constellation....it is not.
The Pleaides (or 7 Sisters) or Messier 45 (M 45) or Subaru
in Japanese....is simply an open star cluster, probably the closest one, IN the constellation of Taurus.  
(Actually there are two Messier objects in Taurus...besides
M-45, Taurus also contains M-1, the Crab Nebula.)

And yes, you are correct, in fact with most open star clusters,
(and the Pleiades are one of the brightest and best in our
night sky), are certainly loosely gravitatonally bound.
And true, most constellation stars are not gravitationally
bound, but simply a line-of-sight arrangement as seen from
the Earth.  But like most open star clusters, in a few million
years some of the stars of the Pleiades will have close approaches to each other, and some will be ejected from the open cluster.

{It is widely thought that the sun also formed up in a similar
small open cluster, which eventually broke up as stars were
ejected from the primordial open cluster.}

But back to M-45....I was not aware of any "mystery"
surrounding the Pleiades....there is good agreement between
the very young, hot,  blue white stars composing this cluster
and their stated distance of only...somewhere between 410
and 425 light years.   And I am not aware of any "anomalous"
factors with regards to this open cluster.  These are large, hot, young, energetic, blue-white stars, much brighter and
larger and hotter than our sun, so naturally they shine so
brightly from that distance of around 400 light-years.

The biggest debate which still goes on, to some extent, involves the nebulosity surrounding the entire group.  At first,  thought to still be the primordial gas and dust in which the cluster first formed up only a few tens of millions of years ago.....or does the cluster just happen to be currently passing through an interstellar dust cloud accounting for the surrounding blue nebulosity?
Most astronomers have switched 180 degrees, and we now
think it just happens to be a passing  interstellar dust cloud causing the nebulosity.  (The brightest part called the Merope Nebula on your star chart).

Sorry, but I'm not up on, or ever been interested in, the
mythology of the night sky.  You'll have to consult with
a different "historical" astronomer with regards to mythology
because I go in for the science, whereas mythology is
non-science.....a "matter of opinion subject"
more a humanities or fine arts subject, of which I have
little or no interest.  I can only think in terms of black and
white with very little grey areas.
Plus, I care less about what the ancients thought of the night sky as in most cases, scientifically speaking, they were wrong (or they just didn't know) on all counts. To me, Orion is not a "hunter" but a specific bound area (like a state) composed of Betelguese, Rigel, the Belt Stars, and two Messier objects, the Great Nebula in Orion (M-42) and the double starred cloud called M-78.  I can only think in terms of science, and no other way.

I do know that "their mother" is one of the Pleiads, but
so is their "father" with the name of Atlas...the
two stars named Atlas and Pleione are the so-called father
and mother of the rest of the Pleiades (it's the two stars
in the 'handle' of what I call the "little sauce pan").
{ I hate to use the word dipper as too  many people confuse
the open cluster with the real "Little Dipper" or Ursa Minor, which starts up by Polaris. } Then the rest of the Pleiads are
the daughters of same, in Mythology.  That's about as far
as I can get you...for more see the website...
http://www.naic.edu/~gibson/pleiades/

Does any further factor stand the Pleiades cluster apart from
............other open clusters?  Only thing I can think of is that
the Pleiades are the only open cluster mentioned in the
Christian Bible...Job 38:31  "canst thou bind the sweet
influences of the Pleiades, or loosen the cords of Orion?"
Other than that, other than being our closest and brightest open cluster, I see no other different factors, except M-45 is one of the youngest and newest of the open clusters in our
night sky.
I doubt if the dinosaurs (65 million years ago) ever saw the
Pleiades because they are so young, but others might
disagree with me.
Hope all this helps, at least to some extent,
Clear skies,
Tom Whiting
Erie, PA