The Pleiades: One of the Best Naked-Eye Deep-Sky Objects

~5 min
The Pleiades: One of the Best Naked-Eye Deep-Sky Objects

The Pleiades (M45, the Seven Sisters) is an open star cluster located at a distance of about 444 light-years from the Earth. It is the nearest Messier object to our planet and one of the most prominent deep-sky objects (magnitude 1.6). To the unaided-eyed observer, it usually appears as a smaller copy of the Big Dipper surrounded by a cloud of dust – a blueish six-star pattern. But why do we call it “the Seven Sisters” then? Let’s figure out where the seventh star is and how to spot the Pleiades in the sky.

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Where is the Pleiades star cluster?

The Pleiades can be found in the constellation Taurus. In the Northern Hemisphere, it’s best to look for it in January and February. In the Southern Hemisphere, the cluster is best seen from December to March.

How to find the Pleiades?

First, find Orion’s Belt and draw an imaginary line through its three stars towards Orion’s bow. The next bright star you’ll see in this direction is Aldebaran – the brightest star of the constellation Taurus and the eye of the celestial bull. Continue the line in this direction, and eventually, you’ll find the Pleiades – a dim blue patch around Taurus’ shoulder.

Where are the Pleiades tonight?

Since the trajectory of the Pleiades is close to the ecliptic, it can be observed from any point except for the Antarctic Circle. To check the position of the star cluster, use the stargazing app Sky Tonight: launch the app and tap the magnifier icon at the lower part of the screen. Then type “Pleiades” in the search bar and tap on the target icon opposite the corresponding search result. The app will show the cluster’s current position in the sky, so you can see if it is visible now in your location.

The stars of the Pleiades

In total, the cluster contains about 1,000 members. Its brightest stars are named after the Greek myth’s characters: the Pleiades themselves – Alcyone, Electra, Maia, Merope, Taygeta, Celaeno, and Asterope (Sterope) – and their parents, Atlas and Pleione. Find them sorted by magnitude in the list below:

  • Alcyone (25 Tauri): 2.86
  • Atlas (27 Tauri): 3.62
  • Electra (17 Tauri): 3.7
  • Maia (20 Tauri): 3.86
  • Merope (23 Tauri): 4.17
  • Taygeta (19 Tauri): 4.29
  • Pleione (28 Tauri): 5.09
  • Celaeno (16 Tauri): 5.44
  • Sterope I (Asterope, 21 Tauri): 5.64
  • Sterope II (22 Tauri): 6.41

How many stars are visible in the Pleiades?

Naked-eyed observers usually spot six stars at a glimpse. However, the longer you look, the more stars you see, given an acute vision and clear skies without light pollution. An American astronomer Robert Burnham Jr. claimed to see 20; most people see no more than 14. Binoculars can give a better view of the cluster and the nebulosity surrounding it. All the brightest stars can be found within a 1° field of view; telescopes with high magnification will help see the fainter ones.

What star is missing?

If most people see the cluster as a six-star pattern, why is it called the Seven Sisters? The reason is that the sky looked different in ancient times when the name was made up. Back then, naked-eyed observers could instantly see seven stars of the cluster. Over time, one of them disappeared from view. Our ancestors noticed and reflected it in myths, which we will discuss later.

The change was caused by Pleione, the seventh-brightest star of the cluster. It is a shell star that varies in brightness; it used to be more prominent but faded below the naked-eye visibility. One more explanation is that Pleione’s position in the sky changed over time, and it came so close to Atlas that the two stars began to look like one to the naked eye.

Myths about the Pleiades

Many cultures have similar stories about the origin of the Pleiades star cluster, possibly inspired by the star's disappearance. Some scientists believe they were made up 100,000 years ago! When the seventh star vanished, ancient people tried to explain that through myths.

For example, the Australian legend tells about the seven sisters who fled into the sky from the old man chasing them; one of the women was captured and saved later. Native Americans had various myths about the seven brothers who rose to the sky while running or dancing in a circle. According to the Cherokee version, one of the boys was caught by his mother and failed to make it to the sky.

The Greek myth is the most popular version of the story. According to it, the Pleiades were daughters of the titan Atlas and the nymph Pleione. After a chance encounter with the sisters, the hunter Orion fell in love and started chasing them. Zeus decided to protect the girls from the unwanted attention and turned the sisters into doves, so they could fly up and become the stars. Before ascending to the sky, one of the sisters, Merope, was married to a mortal, King Sisyphus. When the gods condemned him to roll a boulder forever, she was so ashamed of him that she hid her face and disappeared from the night sky.

Interestingly, in the myth, it is Merope that is referred to as “the lost Pleiad”. But in fact, the missing star that gave rise to the creation of the myth is not Merope, but Pleione, named after her mother.

4 things you probably didn’t know about the Pleiades

  • The Pleiades were mentioned in the Bible three times – all three times along with the constellation Orion.

  • In ancient times, many cultures used the Pleiades as a calendar. By its appearance in the sky, the farmers knew when to start harvesting or planting crops, and the sailors understood when it was time to open the navigation season (the name “Pleiades” was possibly derived from the Greek word meaning “to sail”).

  • The cloud of interstellar dust surrounding the Pleiades is not a part of the cluster. It was believed to be the remnants of the material from which the stars were born. But it turned out that the nebulosity is independent and just happens to be near the Pleiades.

  • The Pleiades inspired the name and the six-star logo of the Japanese car-manufacturing company Subaru (the Japanese name for the cluster). You might have thought the creators wanted to be astronomically accurate and made it look like the Pleiades on the actual night sky. But in fact, the logo illustrates the company's history. In Japanese, “subaru” also means “united”, and the stars represent five small companies that merged into one big – Fuji Heavy Industries, Subaru’s parent company.

F.A.Q.

Who found the Pleiades?

Galileo Galilei was the first to observe the Pleiades through a telescope. However, the star cluster was known long before that: its “origin story” may date back to 100,000 BC. The name of the first who saw the Pleiades in the sky has not been preserved in history.

How old are the Pleiades?

The answer depends on the age-measuring method. For example, if we compare the Hertzsprung-Russell diagram for the Pleiades and theoretical models of stellar evolution, we get figures from 75 to 150 million years.

When can you see the Pleiades?

In the Northern Hemisphere, it’s best to look for it in January and February. In the Southern Hemisphere, the cluster is best seen from December to March.

Can you see the Pleiades with the naked eye?

The Pleiades are in the top 3 best naked-eye star clusters. Most people see it as a group of six stars, but if you have good eyesight and it's dark enough outside, you can spot up to 14 stars.

Thanks for reading our article about the Pleiades star cluster! Now you know when to observe it and how to see more than six (or even seven) stars. You’ve also learned why people see six stars in the Seven Sisters star cluster and that the myth about the lost Pleiad has an astronomical background.

We wish you clear skies and happy observations!

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