Jim's Corner Blog

M45 The Pleiades, Maia Nebula, and Merope Nebula

Unlike most of the other deep sky objects that are either faint or invisible to the naked eye, the Pleiades are a bright sight during the winter and can be seen without any optical aid.

An amateur astrophoto of M45 (John Livermore)

M45 The Pleiades
Alternative Nomenclature: Melotte 22, Seven Sisters, Subaru
Constellation: Taurus
Right Ascension: 03h 47m 24s
Declination: +24º 07′ 00”
Magnitude: 1.6

Maia Nebula
Alternative Nomenclature: NGC 1432
Constellation: Taurus
Right Ascension: 03h 47m 24s
Declination: +24º 07′ 00”

Merope Nebula
Alternative Nomenclature: NGC 1435, containing Barnard’s Merope Nebula IC 349
Constellation: Taurus
Right Ascension: 03h 46m
Declination: +23º 54′ 00”
Magnitude: 13 (IC 349)

Hubble image of the Pleiades reflection nebula near Merope
(NASA and The Hubble Heritage Team (STScI/AURA)

This star cluster has been known to mankind since before the written word. Descriptions and mentions of the Pleiades permeate human culture more than any other deep sky object in this book.

The Pleiades are among the first stars mentioned in written form, with the Chinese writing about the star cluster in 2350 BC.

The Greek myth of the Pleiades tells the story of the Titan, Atlas, who was forced to carry the heavens on his shoulders. Orion began to pursue all of the Seven Sisters, and Zeus transformed them first into doves, and then into stars to comfort their father Atlas and the sea nymph Pleione. The constellation of Orion still pursues them across the night sky to this very day.

Any early mention of the Pleiades can be found in Homer’s Iliad, from about 750 B.C., and the Odyssey, about 720 B.C. From the Iliad:

He made the earth upon it, and the sky, and the sea’s water, and the tireless sun, and the moon waxing into her fulness, and on it all the constellations that festoon the heavens, the Pleiades and the Hyades and the strength of Orion and the Bear, whom men give also the name of the Wagon, who turns about in a fixed place and looks at Orion and she alone is never plunged in the wash of the Ocean.
Iliad 18. 483-89 (translated by R. Lattimore)
Besides the Chinese and the Greeks, the Pleiades appears in the legends and lore of cultures in every inhabited continent on Earth.

The storytelling of the Kiowa tribe in North America tells of the legend of seven maidens transported to the sky by the Great Spirit. The Navajo, the Western Mono Indians, the Inuit, Cheyenne, Cherokee, Hopi, Lakota, Nez Perce and Blackfoot tribes also told their stories relating to this star cluster.

The star cluster appears in the mythology and cultures of the Norse, Celtic, Ukraine, Incas, Aztecs, India, Indonesia, Japan, Philippines, Thailand, Australia, Hawaii, and New Zealand. The star cluster appears in the Swahili language and Sesotho language of Africa.

Even in today’s world, the Pleiades appears in song, literature, and more recently science fiction. Characters and plot lines in Isaac Asimov’s Foundation Trilogy and the television series Star Trek have referenced the Pleiades. A look at the emblem of a Subaru sports-utility vehicle is revealing. The Japanese name for the M45 star cluster is Subaru, and the emblem of the SUV is the Pleiades (or Subaru if you wish!).

The nine brightest stars of the Pleiades are named for the Seven Sisters of Greek mythology: Sterope, Merope, Electra, Maia, Taygete, Celaeno, and Alcyone, along with their parents Atlas and Pleione. As seen in Fig. 8.8 and 8.9, nebulosity accompanies the stellar members of the cluster. American astronomer Vesto Slipher discovered the true nature of the nebulosity in 1912. He noted that the light from the nebulae around the Pleiades had the same features in its spectrum as the light from the Pleiades stars themselves. Hence, the Maia Nebula and the Merope Nebula are reflection nebulae, and the light was being reflected. The nebulae are blue in color because of the light scattering process, similar to the Rayleigh scattering that makes Earth’s sky blue.

Astronomers first believed the dust and gas was left over from the formation of the cluster. However, the proper motions of the stars and of the nebulosity are not the same. The Pleiades are actually moving through a cloud of interstellar dust. Studies show that the dust responsible for the nebulosity is not uniformly distributed, but is concentrated mainly in two layers along the line of sight to the cluster.

The Pleiades open star cluster is estimated to be between 390 to 480 light years away from Earth. There has been much controversy over the distance measurement for the Pleiades. Using the long standard trigonometric parallax methods for determining astrometric distance measures for deep space objects less than 1,000 light-years away, the distance to the Pleiades was determined to be 135 parsecs or 440 light-years away. In 1989, the European Space Agency launched the Hipparcos satellite, designed to perform space distance measurements with great accuracy. The Hipparcos data established the distance as 118 parsecs. This measurement was in conflict with ground-based trigonometric parallax measurements, as well as with Hubble Space Telescope measurements of between 135 and 140 parsecs. The discrepancy has been argued in professional papers, with some resolution appearing after measurements taken with the Very Long Baseline Interfometry (VLBI) and data from the Gaia satellite, which has resulted in a value to 136.2 parsecs, or 444 light-years.

The Pleiades contains over 1,000 stars, many young, hot blue stars. The ages for the Pleiades stars range from 75 to 150 million years.

M45 is moving in the direction of the constellation Orion. Astronomers have determined that within 250 million years, the Pleiades cluster will disperse because of stars being ejected from the cluster due to close encounters with other member stars, tidal gravitational fields moving the stars outside the cluster, and eventual gravitational interactions with the Orion Molecular Cloud Complex.

The Pleiades is the easiest deep sky object to find with the unaided eye. M45 can be seen in almost any suburban location, barring standing in the middle of a brightly lit parking lot. It is an ideal object for binoculars. Use a low power, wide field eyepiece when using a telescope. To see the nebulosity of the Maia Nebula and Merope Nebula, dark skies and larger apertures are required. An eight inch telescope and a nebula filter is quite adequate for the task under suburban skies. The combination of a dark country sky, 4-inch refractor and a broadband nebula filter can also accomplish the task.