The Pleiades star cluster – – famously known as the Seven Sisters or, to some, M45 – is visible from virtually every part of the globe. It’s seen from as far north as the North Pole and farther south than the southernmost tip of South America. It looks like a tiny misty dipper of stars.
If you’re familiar with the famous constellation Orion, it can help you be sure you’ve found the Pleiades. See the three stars in a row in Orion? That’s Orion’s Belt. Draw a line through these stars to the V-shaped pattern of stars with a bright star in its midst. The V-shaped pattern is the Face of Taurus the Bull. The bright star in the V – called Aldebaran – depicts the Bull’s Eye. A bit past Aldebaran, you’ll see the Pleiades cluster, which marks the Bull’s Shoulder.
In our Northern Hemispheres skies, the Pleiades cluster is associated with the coming winter season. It’s easy to imagine this misty patch of icy-blue suns as hoarfrost clinging to the dome of night. Frosty November is the month of the Pleiades, because it’s at this time that the Pleiades shine from dusk until dawn. But you can see the Pleiades cluster in the evening sky well into April.
The star name Aldebaran comes from an Arabic word for follower. It’s thought to be a reference to this star’s forever chasing the Pleiades across the heavens. As a general rule, the Pleiades cluster rises into the eastern sky before Aldebaran rises, and sets in the west before Aldebaran sets.
The only exception to this rule happens at far southern latitudes – for example, at South America’s Tierra del Fuego – where the Pleiades rise a short while after Aldebaran rises.
However, the story about the lost seventh Pleiad appears universal. The astronomer Robert Burnham Jr. found the lost Pleaid myth prevalent in the star lore of European, African, Asian, Indonesian, Native American and Aboriginal Australian populations.
Moreover, Burnham suggested that the “lost Pleiad” may have basis in fact. Modern astronomy has found that the seventh-brightest Pleiades star – Pleione – is a complicated shell star that goes through numerous permutations. These changes cause this star to vary in brightness.
Plus, people with exceptional eyesight have been known to see many more stars in the cluster. Claims go up as high as 20 stars. Agnes Clerke, an astronomer and writer in the late 1800s, reported that Michael Maestlin, the mentor of Johannes Kepler, mapped out 11 Pleiades stars before the invention of the telescope.
To see more than six or seven Pleiades stars, you must have very good eyesight (or a pair of binoculars). And you must be willing to spend time under a dark, moonless sky. Stephen O’Meara, a dark-sky connoisseur, claims that eyes dark-adapted for 30 minutes are six times more sensitive to light than eyes dark-adapted for 15 minutes. The surest way to see additional Pleiades stars is to look at this cluster through binoculars or low power in a telescope.
The Pleiades cluster as a calendar
Historically, the Pleiades have served as a calendar for many civilizations. The Greek name Pleiades probably comes from a word meaning to sail. In the ancient Mediterranean world, the day that the Pleiades cluster first appeared in the morning sky before sunrise announced the opening of the navigation season.
The modern-day festival of Halloween originates from an old Druid rite that coincided with the midnight culmination of the Pleiades cluster. People believed the veil dividing the living from the dead is at its thinnest when the Pleiades culminates – reaches its highest point in the sky – at midnight.
On a lighter note, the Zuni of New Mexico call the Pleiades the Seed Stars, because this cluster’s disappearance in the evening sky every spring signals the seed-planting season.
In both myth and science, the Pleiades are sibling stars. Modern astronomers say the stars were born from the same cloud of gas and dust some 100 million years ago. This gravitationally bound cluster of several hundred stars looms some 430 light-years distant, and these sibling stars drift through space together at about 25 miles per second (40 km/sec). Many of these stars shine hundreds of times more brightly than our sun.
Pleiades photo gallery
Bottom line: The Pleiades – or Seven Sisters – is a star cluster that’s a popular target for observers in the late fall and winter in the Northern Hemisphere.
Bruce McClure served as lead writer for EarthSky's popular Tonight pages from 2004 to 2021, when he opted for a much-deserved retirement. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also wrote and hosted public astronomy programs and planetarium programs in and around his home in upstate New York.
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