North Hawaii News Articles from CFHT
Six Stars, Seven Sisters
Their names are Maia, Electra, Alcyone, Taygete, Asterope, Celaeno and
Merope. They are the seven sisters. They are the Pleiades. Their
mother is Pleione, the Oceanid. Their father is Atlas, one of the
twelve Titans, supporting the world at arms length. That's according
to the Greek Mythology, of course! But one day, a long time ago, it
is said that the Pleiades were travelling with their mother when they
met Orion, the mighty hunter. Orion immediately fell in love with the
beautiful women and started chasing them. The chase lasted for several
years until Zeus, the king of Heaven and Earth and of all the Olympian
Gods, helped them escape by changing them into doves. The doves flew
into the sky and became the stellar cluster we see today, the
Pleiades, still beautiful at 20 million years old, laced with ice-blue
glowing interstellar dust.
The Pleiades are located in the constellation Taurus, the bull, whose
head has a dinstinctive V-shape visible with the naked eye and
featuring the bright and reddish Aldebaran. As expected, Orion can
also be seen nearby, although slightly further East and to the South,
still chasing them. (see the night sky map for February in the
Jan. 27th issue of NORTH HAWAII NEWS )
Since Antique times, people from various cultures, from all over the
world, have assigned myths to the seven stars. Often their appearance
is the signal for a change of seasons. For us living in the Northern
Hemisphere, Makali'i, the Pleiades, become visible at dusk on the
eastern horizon in the fall and signals the arrival of winter. To the
opposite, for people living in the Southern Hemisphere, the Pleiades
rise at dusk in the spring and signal the proximity of the rain
season. To us here and now, and although they have lost a bit of their
mythical influence, the Pleiades still signal winter. They also remain
one of the most recognized stellar cluster in the sky and one the most
beautiful to look at.
The Pleiades can be seen very easily these days, near the zenith
(right above your head!) in the evening, at 20h00. The stars are
fairly bright and together they look like a small version of the Big
Dipper. Six of the stars are clearly visible with the naked eye, seven
if you have a very good vision (I don't!). If you are very patient and
willing to use binoculars, you could probably see a few more. But this
is only the tip of the iceberg. With large telescopes, like those
located atop Mauna Kea, the Pleiades were discovered to actually
contain hundreds of stars, forming what the astronomers call an open
stellar cluster, a group of stars loosely bound together that will
eventually disperse. Today, the cluster spreads over many degrees in
the sky. The seven sisters themselves covering a smaller area, about
half a degree, the size of the full moon.
In Hawaii, the Pleiades are often studied in greater details with the
state-of-the-art instruments of the Mauna Kea Observatories. For
example, recent observations show that a large fraction of the stars
in the cluster are actually twins, binaries. What we thought were
mostly single stars turned out to be mostly close pairs, two stars
orbiting rapidly around one another, a bit like the Earth and the Moon
although with two stars. That's the case for more than half the stars
in the Pleiades!
Another discovery that was made by astronomers (or is it really the
case?) is that a few members of the Pleiades cluster are also well
known for their large variations, their brightness fades and increases
by large factors over the years. The ancients obviously knew that
before us as they claim that Merope, one of the sisters, was so
ashamed to have had a mortal husband, Sisyphus, that she vanished,
deserted her sisters. That's why we only see six of the seven Sisters
today... without a telescope that is.
Francois Menard
Visiting Scientist
Canada-France-Hawaii Telescope Corporation