The Pleiades (M45), also known as the Seven Sisters, is one of the most striking and recognizable star clusters in the entire night sky. Visible from every part of the planet, from the North Pole to below the southernmost tip of South America, it has also captivated the imagination of stargazers for centuries and holds significant cultural importance across various civilizations.
Let’s explore some more fascinating facts about this celestial wonder:
Quick Facts
- Coordinates: RA 03h:47m:24s, Dec +24°07’
- Constellation: Taurus
- Distance: 444 light-years
- Magnitude: 1.6
- Star Type: Blue (B8IVpe)
- Mass: 800 solar masses
- Designations: Pleiades, Messier 45 (M45), Melotte 22, The Seven Sisters.
1. Star Cluster Status
The Pleiades is an open star cluster, meaning it is a group of stars that formed from the same giant molecular cloud and are loosely bound by gravity. The age of the Pleiades cluster is estimated to be around 100 million years old, making it relatively young in astronomical terms. Of the 1,000+ stars this cluster contains, most are of the hot blue luminous variety, although only a handful are visible to the naked eye.
2. Located in Taurus Constellation
The Pleiades is relatively close to Earth compared to other star clusters, lying at a distance of about 444 light-years away in the constellation of Taurus. Stargazers can easily locate the Pleiades by imagining a line running through Orion’s belt, past the red star Aldebaran in the constellation Taurus onto this beautiful open cluster of blue stars. In the northern hemisphere, the Pleiades are associated with the winter months, but can be seen from autumn all the way through to April. In the southern hemisphere, it can be seen during late spring and summer.
3. Five Brightest Stars
Despite its nickname, the Pleiades actually consists of more than seven stars. However, only five stars are typically visible to the naked eye under optimal conditions. These stars in order of magnitude of brightness are — Alcyone (2.86); Atlas (3.62), Electra: (3.70), Maia: (3.86), and Merope (4.17). In ancient times, being able to discern the individual stars of the Pleiades cluster was considered a measure of one’s visual acuity. In 1610, Galileo first observed the cluster through a telescope, and could see more than forty stars using his refractor.
4. Mythological Roots
In Greek mythology, the Pleiades were seven sisters, daughters of the titan Atlas and the sea-nymph Pleione. The sisters’ names were Alcyone, Maia, Electra, Merope, Taygeta, Celaeno, and Sterope (also known as Asterope). They were pursued by the hunter Orion, and to protect them, Zeus transformed them into stars. However, one sister, Merope, married a mortal man, and her fainter appearance among the visible stars is said to represent her shame.
5. Cultural Significance
The Pleiades hold cultural significance across many civilizations throughout history. In Japanese folklore, it is known as Subaru, which inspired the name of the automobile manufacturer. Indigenous peoples of North America also have myths and stories associated with the cluster, often regarding it as a group of siblings or a camp of celestial beings. Similar stories can be found in the indigenous cultures of Australia and New Zealand, as well as India and China.
6. Structure of the Pleiades
Spread out over an area of around 13 light years, the cluster is made up of two distinct regions, one being a central, almost spherical core that contains around 100 stars over an area of just more than 4.5 light years, and the other is an outer, less densely populated region. The Pleiades itself is made visible by 14 or so hot blue stars with luminosities that range between 40 and 1,000 times the Sun’s luminosity. Other stars found in this cluster include a large number of brown dwarfs, and several white dwarfs.
7. Blue Reflection Nebula
The Pleiades reflection nebula is a faint blue haze surrounding the cluster’s brightest stars, particularly Merope. It is visible due to the scattering of starlight by dust grains in the interstellar medium. These dust particles are illuminated by the stars within the cluster, causing them to reflect and scatter light, predominantly in the blue wavelengths. The wave like appearance of the cloud is the result of the interaction of multiple factors, including the action of Merope’s solar wind on the different constituents of the cloud.
8. The Pleiades and the Hyades
The Pleiades and the Hyades are both star clusters located in the constellation of Taurus. While they appear close together in the sky, they are actually two distinct clusters and are not physically related to each other. They simply appear close together from our perspective on Earth. The Hyades is located just 153 light-years away, is older than the Pleiades at around 625 million years old, and is composed of hundreds of stars. One of the most prominent stars in the region of the Hyades is Aldebaran, which is often mistaken for being part of the Hyades cluster but is actually much closer to Earth and not gravitationally bound to the cluster.
Conclusion
The Pleiades stands as a testament to the dynamism of the universe, showcasing the birthplaces of stars and the interconnectedness of cosmic phenomena. Whether observed through a telescope or revered in myth and legend, the Pleiades remains a beacon of cosmic beauty, inviting us to ponder the mysteries of the cosmos and our place within it.
