10 ASTRONOMY • JANUARY 2022
8 The Pleiades
Visible to the unaided eye as a tiny congregation of stars due west of
Taurus’ V-shaped head, the Pleiades (M45), also known as the Seven
Sisters, is one of the sky’s premier open star clusters. Under typical
suburban skies, you might be able to count five or six stars set in the
shape of a tiny dipper. Move to darker skies, though, and that number
could double or even triple.
One reason the Pleiades puts on such a grand show is because it
is only about 445 light-years away. That makes it one of the closest
clusters to Earth. Just how many stars belong to the Pleiades depends
on the source you quote. Some will say about 200, while others will
claim more than 1,000. Studies suggest that Pleiades’ stars are roughly
100 million years old — mere infants compared to the Sun.
Photographs of the Pleiades show they are immersed in blue
reflection nebulae. Originally, astronomers believed that the nebulosity
was leftover material from the cluster’s formation. Recent studies,
however, show that the nebulae and the cluster are moving throughspace at two different velocities, proving these objects are indepen-
dent and just happen to be currently passing each other on their
separate journeys through the cosmos.
The Pleiades spans nearly 2°, making binoculars and wide-field
telescopes best for taking in the view. There are several striking
binary and multiple stars within M45. The star Atlas, shining at
magnitude 3.7, together with Pleione, which varies in brightness
from magnitude 4.8 to 5.7, form a wide pair that marks the eastern-
pointing handle of the shrunken dipper’s bowl. Asterope is also a
wide pair of stars, while Alcyone, the brightest Pleiad, is a quadruple
star system.
Given an exceptionally clear evening, look closely for soft gos-
samer wisps of the dust surrounding some of the Pleiades’ brighter
stars. The brightest portion of the cluster's nebulosity is identified
as NGC 1435 and sits near Merope, the southeastern star in the
Pleiades’ bowl. — P. H.