07-15-2009 - clusters nebulae galaxies

How to see it

The Pleiades star cluster – also known as the Seven Sisters or M45 – is visible from virtually every place where humanity inhabits the globe. This tiny dipper of stars can be seen from as far north as the north pole, and farther south than the southernmost tip of South America. If you’re familiar with the constellation Orion, draw a line through the three stars of Orion’s Belt to find the bright star Aldebaran, which depicts the eye in the constellation Taurus the Bull. A bit past Aldebaran, you’ll see the Pleiades cluster, which marks the Bull’s shoulder.

Aldebaran, Arabic for follower, is thought to be in reference to this star 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 – like at South America’s Tierra del Fuego – where the Pleiades rise a short while after Aldebaran rises.

In our northern hemisphere, the Pleiades cluster is associated with the 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 often called the month of the Pleiades, because it’s at this time that the Pleiades shine from dusk till dawn. Beyond November, the Pleiades cluster continues to adorn the evening sky well into April.

The Lost Pleiad

Most people see 6, not 7, Pleiades stars in a dark country sky. However, the story about the lost 7th Pleiad harbors a universal theme. The astronomer Robert Burnham Jr. finds the lost Pleaid myth prevalent in the star lore of European, African, Asian, Indonesian, Native American and Aboriginal Australian populations. Moreover, Burnham suggests the “lost Pleiad” may have basis in fact. After all, modern astronomy has found that the 7th brightest Pleiades star – Pleione – is a complicated and hard-to-understand “shell star” that goes through numerous permutations. These changes cause this star to vary in brightness.

The number of Pleiades stars visible to the unaided eye is open to question. Claims go up as high as 20 stars. Miss Agnes Clerke reports that Maestlin, the tutor of Kepler, mapped out 11 Pleiades stars before the invention of the telescope. However, you must be willing to spend time under a dark, moonles sky to see more than 6 or 7 Pleaides stars. Stephen O’Meara, a dark-sky connoisser, claims that eyes dark-adapted for 30 minutes are 6 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.

Calendar History and Modern Science

Historically, the Pleiades have served as a calendar for many civilizations. The Greek name “Pleiades” probably means “to sail.” In the ancient Mediterranean world, the day that the Pleaides 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. It was believed that the veil dividing the living from the dead is at its thinnest when the Pleaides 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 considered to be sibling stars. Astronomers say the Pleiades 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. Many of these Pleiades stars shine hundreds of times more brightly than our sun.

Written by Bruce McClure

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