Introduction:
The Pleiades (The Seven Sisters or Messier 45 (M45) is classified as an open star cluster. It is usually misunderstood that they are only a group of seven stars due to its misleading name, but it is actually composed of over 1,000 stars that are weakly bounded by gravity. It is about 445 light years away and is located in the constellation of Taurus the Bull. Due to their remarkable bluish-wispy color and their luminosity that makes them enough to be seen by the naked eye, they have always been easily recognized and distinguished in the night sky. This resulted in the fascination and marvel of countless stargazers and the birth of numerous tales. The Pleiades are a young star cluster approximately only 100 million years old. The asterism is best observed during the winter as they are winter stars. They are visible all night throughout November and December.
The cluster's major stars, known as hot B-type stars, emit enormous energy and generate considerable amounts of blue light. The exquisite wispy blue glow around the Pleiades stars is created by the surrounding nebula that is fittingly named 'Reflection Nebulae'. The interstellar dust and cloud reflect this light to cause that effect. The cluster consists of an abundance of brown dwarfs or failed stars. These celestial bodies, while larger than planets, lack the mass to spark nuclear fusion processes in their cores and explode into life as stars. The names of the infamous Seven Sisters are Alcyone, Asterope, Celeano, Maia, Merope, and Taygete. Although they are called the Seven Sisters, only six are visible to the naked eye. Merope is considered the Lost Sister due to being the faintest star from the seven and the last one to be charted.
The young age of the stars in the Pleiades cluster, combined with their brightness and distance to Earth, has made them a focal point for astronomers to study stars' early formation and evolution. Their influence in astronomy is invaluable as they allowed scientists to study the mechanics of star birth, motion, and clusters in much more detail.
Star Cluster Information:
Coordinates | RA 3h 47m 24s | Dec +24° 7′ 0″ |
Apparent Magnitude (V) | 1.6 |
Core/Central Radius and Diameter/ Tidal radius | 8 light years(core), 43 light years (diameter) |
Radial velocity / Redshift / cz | V(km/s) 5.88 [0.03] |
Proper motions mas/yr | 19.997 -45.548 [0.127 0.101 90] B |
Parallaxes (mas) | 7.364 [0.005] B |
Angular size (arcmin) | 76.86 76.86 ~ (Opt) C |

Stellar characteristics of the brightest star in the Pleiades; Alcyone:
Properties | Alcyone |
Coordinates | RA 3h 47m 29s | Dec +24° 6′ 19″ |
Parallax(π) and Distance | 8.09 ± 0.42 mas 136 pc (distance) |
Proper motions mas/yr | 19.34 -43.67 [0.39 0.33 90] A |
Radial Velocity | 5.40 km/s |
Spectral type | B7IIIe |
Surface temperature | 12,258 K |
Mass | 5.9 – 6.1 M ☉ |
Apparent magnitude | 2.85 |
Figure 2:
* Note that the two other stars were named Atlas, and Pleione for their relevance in the mythology behind the origin of their names. Asterope is also called Sterope*
Image captured by Hubble Space Telescope (2)

Birth/Origin and life expectancy:
Since M45 is a star cluster, it does not only mean that they formed around the same time but that they are also made from identical material- this makes them a stellar family. M45 was born as a result of a cloud of gas and dust collapsing due to the influence of gravity. This resulted in intensely high temperatures which allowed for the stars to form.
Most of the stars in the Pleiades are classified as young B-type stars, which burn hydrogen to generate energy. The stars consume the energy on huge scales rapidly. Unfortunately, as a result of their intensity and high temperatures, the Pleiades are expected to have a short life span expectancy. They will burn up with expected life spans of only around a few hundred million years. Depending on the mass of the B-type star, if it's sufficient enough it might go supernova and then turn into a nebula. However, if its mass is inadequate, it might enlarge into a red giant and dissipate into a white dwarf.

Mythologies and History:
The Pleiades’ mesmerizing prominent arrangement in the sky has caught not only stargazer’s attention but has also aided navigators and farmers in their tasks and lives. Although it is said that the first person that observed the asterism through a telescope is Galileo Galilei, it does not mean that the group of stars were not a keen subject of interest to ancient civilizations. The Pleiades have been recorded in what is believed to be the oldest star map in history which is called the Nebra Disk. The Nebra Disk dates back to the bronze age; it proves the significance of these stars as it aided in deciding when to synchronize the lunar and solar years. This happened by adding a leap month when both the Pleiades with the crescent on the disk (three-and-a-half-day-old moon) were visible together.

The Seven Sisters were also commonly used in astronavigation, known as celestial navigation. Where it was crucial in determining their current position, this was most beneficial for sailors. They also were instrumental in the timing of seasonal activities like harvesting and planting crops with their observable rising and setting patterns. The Pleiades have been included in various cultures and mythologies, further emphasizing its effect on not only astronomy but also cultural aspects. They have been featured in almost every ancient civilization’s story, including the Greeks, Romans, Hindus, Mayans, Māori, Egyptians, Chinese and many more.
● Greek Mythology: The current stars are named after those who appear in the myth of the Seven sisters, a story that includes the origin of the Pleiades. Alcyone, Asterope, Celeano, Electra, Maia, Merope and Taygete were daughters of the Titan Atlas and the Oceanid nymph Pleione. The myth tells that the sisters were pursued by the giant huntsmen Orion. Atlas who was unable to protect his daughters was cursed by Zeus to hold up the heavens on his shoulders. Zeus took pity on Atlas’s daughters and transformed them into the stars that make up the Pleiades cluster.
● Hindu Mythology: In India, the Pleiades are all referred to as Krittika, the spouses of the seven wise men known as the 'Seven Rishis' or 'Seven Sages', or the six mothers of the battle deity Murugan, who developed six faces, one for each. They carry immense value in Vedic and Hindu astronomy, astrology, and culture. Celebrations involving the stars are an integral part of the Hindu calendar, such as the Karthika Deepam festival celebrated in Tamil Nadu.
● Māori culture: In the Māori culture, the Pleiades are seen as a 'celestial net' or 'the net of Māui' and are associated with fishing and cultivation. They are called Matariki which represent the seven stars. The appearance of the stars before dawn in mid-winter marks the New Year for the Māori. Matariki symbolizes a time of peace, happiness, togetherness and remembrance. It is a moment for communities to unite and celebrate.

Conclusion:
Stars are timeless capsules that hold billions of both told and untold stories. The Pleiades, to many people, are more than just a cluster of young hot stars - they are stories and tales that have been constant in the night sky throughout time immemorial. Whether you look up on a clear winter's night and see the sisters shine brightly or catch only a glimpse through the clouds, there is no doubt that they will continue to captivate and fascinate future generations to come. Their astronomical prominence and their symbolic significance in cultures worldwide, speaks to the profound impact the Pleiades have had on humanity. For both an astronomer and a stargazer Messier 45 or the Seven Sisters will always be a sight to behold.
References:
What are the Pleiades? (n.d.). Royal Museums Greenwich. Retrieved from https://www.rmg.co.uk/stories/topics/what-are-pleiades
Messier 45 (The Pleiades) - NASA Science. (n.d.). Retrieved from https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-45/
Bernard, S. (2024, January 4). Alcyone - Star facts - Online Star Register. Online Star Register. Retrieved from https://osr.org/blog/astronomy/alcyone/
ThePlanets.org. (2024, March 27). Alcyone star: Facts about the brightest star in the Pleiades. Retrieved from https://theplanets.org/stars/alcyone-star/
Pleiades. (n.d.). SIMBAD. Retrieved from https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=Pleiades+&submit=SIMBAD+search
The Nebra Sky Disk. (n.d.). Retrieved from https://www.celticnz.co.nz/NebraSunDisk/NebraSunDisk.htm
Archaeology Magazine. (2024, May 30). Mapping the past - The Nebra Sky Disc - Archaeology Magazine - May/June 2019. Retrieved from https://archaeology.org/issues/may-june-2019/collection/maps-germany-nebra-sky-disc/mapping-the-past/
MYTHS AND LEGENDS | Lucinda Riley. (n.d.). Retrieved from https://lucindariley.co.uk/myths-and-legends/#:~:text=The%20Western%20Mono%20Indians%20believed,the%20sky%20and%20become%20stars
Karthigai Festival | Tiruvannamalai District, Govt. of Tamil Nadu | India. (n.d.). Retrieved from https://tiruvannamalai.nic.in/karthigai-festival/#:~:text=Another%20legend%20links%20karthigai%20Deepam,after%20by%20six%20krittika%20stars
McClure, B., & McClure, B. (2024, November 14). The Pleiades – or 7 sisters – known around the world. EarthSky. Retrieved from https://earthsky.org/favorite-star-patterns/pleiades-star-cluster-enjoys-worldwide-renown/
Hubble Refines Distance to the Pleiades Star Cluster. (n.d.). HubbleSite. Retrieved from https://hubblesite.org/contents/media/images/2004/20/1562-Image.html
International Astronomical Union | IAU. (n.d.). The Pleiades. Retrieved from https://www.iau.org/public/images/detail/ann22042ab/
information@eso.org. (n.d.). The Pleiades. European Southern Observatory. Retrieved from https://www.eso.org/public/images/b11/#:~:text=The%20cluster's%20central%20region%20spans,estimated%20at%2043%20light%2Dyears
-Authored by: Lilian Jan from The Eunolia.
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