UpDate - Vol. 11, No. 17, Page 7
January 23, 1992
Sky High; Legendary Seven Sisters recognized by Homer, Job

     So small, so faint and yet so famous! When you look high
overhead these January evenings, that tiny, but very distinctive,
group of stars, so small that your thumb at arm's length will cover
them, has had a special place in human imagination throughout all
of recorded history.
     The Pleiades, the Seven Sisters, the legendary daughters of
Atlas and Pleione, rank right up there with the Great Bear and the
giant, Orion.
     Yet the Pleiades do not, themselves, constitute one of the 88
constellations as presently defined by international agreement.
Such stellar configurations, that are not constellations as the
term is now used but are given a separate identity because of their
apparent association together in the sky, are called asterisms.
     Our western tradition puts the Seven Sisters within the
zodiacal constellation of Taurus, but in legend they are often
associated also with the more prominent Orion who pursues them
across the sky. References to the Pleiades are found in the oldest
extant writings: Homer, Job, Egyptian Hermetic books, Chinese
annals from 2357 B.C. Many people are familiar with the biblical
passage where the Lord points out to Job his many mortal
shortcomings: "Canst thou bind the sweet influences of the Pleiades
or loose the bands of Orion?"
     Part of the enchantment that we feel in knowing the sky well
enough to be able to recognize old constellations and asterisms,
such as Orion and the Pleiades, is a communion with those of the
past who also knew the sky. Wherever our ancestors lived on the
world, excepting Antarctica, there were those among them who knew
the Pleiades. At night, when our modern surroundings are vignetted
by darkness, we can look up to see virtually the same sky they saw
and delight in tracing the same constellations they knew.
     Of course the names by which they were known in various
cultures differed. They were Mata-riki, the "Little Eyes," to the
Polynesians, who had a charming story that they were once a single
star, the most brilliant in the sky. This star's boastfulness
annoyed the god Tane who was in charge of the four pillars of
heaven.
     Tane threw Aldebaran at the boastful star, breaking Mata-riki
into the fragments that we now see. The legend has a triumphant
ending for vanity when the fragments see themselves reflected in
the oceans and realize that they are more alluring as a cluster of
stars than they were as a single, bright star.
     To the Mongols, the group was the Monkey; the Finns and
Lithuanians called it the Sieve with holes in it. In Arabia, it was
the Herd of Camels and, in many places, it was known as the Hen
with Her Chicks. Some of the names are more descriptive of the
arrangement of the stars. We hear it described as a "little
dipper," which, although a true enough rendering of its shape, is
confusing because this is not the official Little Dipper, that
being the constellation Ursa Minor, the little bear, that contains
Polaris in the northern sky.
     Because an automobile manufacturer has adopted this cluster as
a logo, the Japanese name for the Pleiades, Subaru, is known to
many Americans. I have been unable to trace any mythology behind
this name. If any readers can help me out, I would be pleased to
hear from them.
     Surprisingly often, diverse legends identify these stars with
women or girls. But, most strangely, the number specified is
frequently seven. What makes this remarkable is that the number of
stars readily seen today is only six. Look for yourself. If you are
favored with a clear, dark sky and excellent farsightedness (or
recently prescribed eyeglasses), you may see more than six. But, if
you do, you will see more than seven, for several stars are tied
for the status of seventh brightest star.
     Actually, and unlike almost all constellations, the Pleiades
is a group of stars physically associated together in space, not
just an accidental assemblage of near and far stars that appear
together because they are seen in the same direction. Astronomers
call such a group an "open" cluster because of the loose way it is
spread out without a high concentration of stars at the center.
     With binoculars (highly recommended for viewing the Pleiades)
you will see many more stars. Use the enlarged insert at the lower
right of the sky map to judge how many Pleiads you can detect with
the naked eye and/or with binoculars. The number will depend
strongly on how bright the sky background is. Open clusters often
contain a hundred or more stars, and this is true also of the
Pleiades. With the naked eye, we see only the handful of most
luminous members. Most star clusters are too far away to be seen at
all without binoculars or a telescope.
     However, here in Taurus, there are TWO open clusters near
enough for the unaided eye to discern individual stars. The second
is the Hyades, in myth the daughters of Atlas and Aethra and, thus,
half-sisters of the Pleiades. The Hyades are closer than the
Pleiades and appear more dispersed in the sky. Incidentally,
Aldebaran is not physically a member of the cluster but stands
about half way between us and the Hyades cluster.
     So, why don't the myths agree on the number of stars in the
Pleiades? Some say six, some say seven, and some even relate that
there are seven but one has gone away or is hiding! Perhaps one of
the fainter stars was once brighter. Stars are known to change
their brightness, but, generally not on the time scale that we
infer from the mythology. If a faint member of this cluster was
once bright for an extended period of time, astronomers would love
to know which one.
                                          - Richard B. Herr
                               Associate Professor of Physics and Astronomy