Sky & Telescope - December 2021 - 45

Evenings with the Stars by Fred Schaaf
Seeing
the Seven
Sisters
One of the sky's finest
open clusters has quite
a tale to tell.
T
he Pleiades, or the Seven Sisters as
they're also called, is more than just
the loveliest star cluster for naked-eye
observers. The sight is so distinctive
that it has been mentioned in countless
legends and great literature throughout
history, and it has even appeared in
modern advertising.
About two millennia ago, the Druids
used the date of the cluster's sunset
rising to mark the beginning of their
year and the Celtic holiday Samhain,
which later evolved into Halloween
( " All Hallows' evening " ). You may be
reading this column around Halloween,
but whenever the Pleiades are above the
horizon you should have little trouble
finding them - so long as your sky isn't
washed out by urban light pollution,
bright moonlight, or both!
The Pleiades are shown high above
the eastern horizon on the Sky Chart
presented on pages 42 and 43, which
depicts the evening sky at different
times from late October to the end of
December. At the chart times given,
the cluster floats directly above orange
Aldebaran and the Hyades - all three
sights residing in the constellation
Taurus, the celestial Bull. Below Taurus
is the low, tilted form of brilliant
Orion, with its conspicuous three-star
Belt spanning 3°. But unlike the Belt
asterism, the Pleiades are a true cluster
of stars gravitationally bound to each
other as they travel through space.
How far away are the Pleiades?
Back in 2009, the International Year of
Astronomy commemorated the 400th
anniversary of the year Galileo first
pALL THAT GLITTERS The stars of the Pleiades cluster are moving through space together and
passing through a cloud of dust, creating the picturesque haze surrounding the brightest Pleiads in
this photo by Alan Dyer.
aimed his telescope skyward. In 2009,
estimates pegged the cluster's distance
at 400 light-years - a coincidence I took
advantage of when I showed the Pleiades
to the public. I was able to tell them
that the light they were seeing began its
journey in 1609, as Galileo was making
his monumental observations, Kepler
was publishing his first two laws of
planetary motion, and Shakespeare was
nearing the end of his brilliant career.
Now, in 2021, the latest research places
the cluster a little farther away, at 446
light-years (see S&T: Mar. 2019, p. 26).
The cluster represents the Seven
Sisters of Greek mythology, and is so
lovely and delicate that it's associated
in legends with maidens, doves, or even
a mother hen with its brood of chicks.
The geometric shape formed by the
cluster's brightest stars is most often
pictured as a tiny Dipper - a design
that will be especially familiar to owners
of Subaru cars.
The number of naked-eye Pleiads
visible to the person with average
eyesight under average sky conditions
may be seven, but is more likely to be
just six. This disparity has led to the
legend of " the Lost Pleiad. " In his poem
" The Good Night " the 19th-century
English writer Alfred Austin alluded
to the missing star in his beautiful
lines, " The Sister Stars that once were
seven/Mourn for their missing mate in
Heaven. "
Part of the reason some observers
see fewer than seven stars is the tight
pairings of several cluster members. For
instance, the stars of the tiny dipper's
handle, named for the Seven Sisters'
parents, Atlas and Pleione, shine at
magnitudes 3.6 and 5.1 but are only
about 5′ apart. The bowl of the tiny
dipper is formed by stars named for the
individual Sisters. Working counterclockwise
from 2.8-magnitude Alcyone
(the brightest Pleiad) they are: Merope,
Electra, Celaeno, Taygeta, Maia, and
Asterope, which is a wide double star
just north of Maia.
A total of nine Pleiades stars are
magnitude 5.6 or brighter, but under
excellent sky conditions careful observers
can observe several more without
resorting to optical aid. The eagleeyed
Stephen James O'Meara has seen
17 Pleiads, and the record is held by
the great Walter Scott Houston, who
counted 18.
¢ FRED SCHAAF was able to glimpse 12
individual Pleiads with the unaided eye
in his youth.
sk yand tele scope .o r g * DECEMBER 2021 45

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Sky & Telescope - December 2021

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