The Pleiades is one of the most recognized sights in winter’s night sky. It was recorded long before the first telescopes by the Chinese and is mentioned in the Bible.
Also known as the Seven Sisters, Charles Messier included it in his catalog of Messier Objects, which is why it also has the more boring designation of M45.
However, on your binoculars or telescope, this is far from a boring sight. It is a beautiful, tranquil, and entirely mesmerizing object and, in this article, we’re going to help you find the Pleiades and enjoy observing it.
The Pleiades – Vital Statistics
|R.A. (2000.0)||03h 47m 00s|
|Dec. (2000.0)||+24° 07′ 00″|
|Apparent Size||120 arcminutes|
What are the Pleiades?
The Pleiades is an open cluster of stars. The stars all travel through space together because they were formed from the same huge cloud of gas and dust.
Their birth is believed to have happened around 125 million years ago. We’re not sure how many of them there are, but it’s at least 800 and may be as many as 3,000.
The brightest nine stars are named after the seven sister nymphs and their parents Atlas and Pleione. And they are bright stars, hundreds of times brighter than our Sun. The brightest star in the cluster, Alcyone, shines over 1000 times brighter than the Sun.
To put that into context, Alcyone has a visual magnitude of +2.9. If we were to fly out to Alcyone and look back at the Sun from there, we would see it shining at a dim magnitude +10.
The stars in M45 are so bright because the fusion process at their core is taking place at a ferocious rate. Other than making the stars bright, this intense burning of their fuel also means they will have short lives for a star. They are expected to die in a few hundred million years, living in total for less than 10% of our Sun’s predicted lifespan.
When we observe the Pleiades, we are seeing what they looked like over 400 years ago because they are about 430 light-years away from our planet, in the constellation of Taurus.
In total, the cluster spans more than 40 light-years from edge to edge, but the brightest part that we can see with the naked eye is just 8 light-years wide. In our sky, that roughly equates to a 2° field of view, or four times the width of the full Moon.
The Brightest Stars of the Pleiades
There are nine stars in the Pleiades brighter than magnitude 6.0 and technically visible to the naked eye under dark skies. See each of them labeled in the diagram below. Click it for a larger version.
All of the stars are hot class B, with temperatures in excess of 12,000 Kelvin. Let’s look at them in a little more detail from brightest to dimmest.
Alcyone (Eta/25 Tauri) – This is the brightest of the Pleiads and the third brightest star in Taurus.
Alcyone is a multiple star with four orbiting companions shining at magnitude 2.9, 6.2, 8.3, and 9.1. The D component is also believed to be a double and the A star is a triple.
Atlas (27 Tauri) – The second-brightest star shines at magnitude 3.6 and is also a double. Its companion is a faint magnitude 13.2 and is 95″ away.
Electra (17 Tauri) – Also a double, the main component shines at magnitude 3.7, the companion is 99″ away shining at magnitude 13.0.
Maia (20 Tauri) – The fourth-brightest Pleiad shines at magnitude 3.9 and has a companion 113″ away which is magnitude 13.7.
Merope (23 Tauri) – Another bright star with a faint companion. Separated by 110″, the two stars shine at magnitude 4.2 and 14.4 respectively
Taygeta (19 Tauri) – Continuing the stream of doubles, the two components of Taygeta shine at magnitude 4.3 and 11.0. They are 72 arcseconds apart.
Pleione (28 Tauri) – This is the seventh-brightest star in the Pleiades and shines at magnitude 5.1. And, yes, it too has a companion. The B star is magnitude 12.0 and 168 arcseconds from the A.
Celaeno (16 Tauri) – There are two stars in this system as well, separated by 88″. The brighter of the two is magnitude 5.5, the fainter in magnitude 13.2.
Sterope, Asterope (21 & 22 Tauri) – Interchangeably known as Sterope or Asterope, this ninth-brightest Pleiad gives a full-house of doubles. The two components are both bright, at magnitude 5.8 and 6.4 respectively, and are 150 arcseconds apart.
Nebulosity in the Pleiades
The whole cluster is shrouded in nebulosity, which shows wispy blue tendrils in astrophotography images like that towards the bottom of this page.
For a long time, it was believed that the nebulosity was the remains of the gas and dust field that had given birth to the individual Pleiads, but we now believe that is not the case.
Scientists now think that the cluster is passing through a region of space that is denser with dust and gas. The light from the stars reflects off the dust and creates a reflection nebula.
You’ll have to discover for yourself how much nebulosity you can see, which is dependant on the quality of your sky, equipment, and observation skills. Our observation guide at the end of this article tells you what to look for.
When Can We See the Pleiades?
Since it rides so close to the path of the Sun, and we can all see the Sun from anywhere on Earth, it follows that the Pleiades can also be seen from practically anywhere on the planet. The only place it is never visible is inside the antarctic circle.
The flip side of most of us being able to see it is that it is not circumpolar but seasonal, i.e. it is only above the horizon at certain times of the day. The table below shows when the Pleiades is in the sky for mid-latitudes of the northern hemisphere.
Northern Hemisphere Visibility
Let’s take a look at when is the best time of year to point your telescope towards the Pleiades in the northern hemisphere.
This table shows when you can best see the Pleiades from the mid-latitudes of the northern hemisphere. Times shown are approximate local times for mid-month using a 24hr clock.
Times shown underlined are during hours of darkness
As you can see from the table, the Pleiades are best observed in the evening in winter. In November, for example, the Seven Sisters is visible from sunset until dawn.
Indeed, this beautiful cluster offers great evening viewing from October until April. If you’re more of a morning astronomer your viewing opportunities are more limited because of shorter summer nights, but you can still enjoy finding the Pleiades from June to September.
The only time of the year when we can’t really see the Pleiades is when it gets too close to the Sun during May and June.
How to Find The Pleiades
M45 is such an obvious sight that, once you’ve found it for the first time, you’ll always be able to pick it out again without much trouble.
However, the first time you try to locate it, it is easier to use an obvious starting point and move from there to the Pleiades in a process known as star-hopping.
Fortunately for all of us, our starting point is the unmistakable constellation of Orion the Hunter. More specifically, we’re going to use the hunter’s belt to point the way for us. It is circled in the SkySafari 6 picture below.
The star Aldebaran is also highlighted with a green arrow because this very bright star in the constellation of Taurus is part of the star-hop which takes us to the Pleiades.
Imagine a line that follows Orion’s belt from its lowest to highest side. Extend it to run to Aldebaran, then continue it until it hits a bright but fuzzy patch of stars. That fuzzy mass is the Pleiades, a.k.a the Seven Sisters, a.k.a M45.
Let’s put all of that into the simple chart below, which you can click on for a full-screen version.
Now you know how to locate them, where exactly do you need to look if you’re observing in summer, fall, or winter?
Where to Look for the Seven Sisters
The images below show where to look for the Pleiades in winter evenings and late summer/fall mornings. Stars are shown to magnitude 6.0 and the images are taken from SkySafari 6.
Each image can be clicked on to open a full-screen version in a new tab.
In the image above, you can see the Pleiades are about 50° over the eastern horizon at 10pm in the middle of November, which is about midway between the horizon and overhead point.
This is the scene for observers in the mid-US latitudes. If you are further north, the cluster will be lower in the sky and vice versa if you are further south.
The next image shows the position as spring begins. The Pleiades is highest in the sky as dusk fades, which is why this image shows where to look at 8:30pm in the middle of April.
Finally, let’s take a look at a morning view of the Pleiades, which is the best time of day to see it in late summer and early fall.
On a mild but crisp morning in late September, the Seven Sisters is riding almost overhead and is a beautiful summit to the canopy of pre-dawn stars.
What Can You See When You Look at the Pleiades?
Although it’s called the Seven Sisters, there is a large variety in the number of stars that can be seen with the naked eye.
As we saw earlier, nine stars are brighter than magnitude six, meaning they should be visible to anyone with decent eyesight in a dark sky location.
However, many observers only report seeing six stars, causing the dimmest of the sisters, Pleione, to be nicknamed ‘the lost pleiad’. Other observers have recorded seeing eleven or more, including Michael Maestlin who saw up to fourteen before telescopes (or street lighting) were invented.
There’s an adage in astronomy that applies well here: the more you look, the more you’ll see. Put simply, as you study this cluster more and become more familiar with it, new details will become clearer to you and you will see more stars. Make sure to spend time outside letting your eyes adjust to the dark first though.
What else can you expect to see when observing the Pleiades? Let’s answer that question based on the equipment you’re using to study them.
To the naked eye, the Seven Sisters appears as a tight cluster of stars wrapped in a cloudy nebulosity.
Depending on the quality of your skies and eyes, you may see the brightest stars in the pattern of a mini dipper.
How many individual stars can you make out within the cluster?
Astronomy binoculars provide some of the best views of the Pleiades. Their low magnification delivers a wide field of view which is needed to fully appreciate the splendor of this cluster.
Although binoculars have low magnification, it is more than enough to reveal many more stars in the cluster than you can see with the naked eye alone.
There’s a dilemma to face when using our best telescope to look at the Pleiades.
We either need to keep the magnification on the lower end and enjoy the panorama of blue-white diamonds densely littering the sky, or we need to push in hard and hunt for fainter members of this group.
Most observers prefer a lower magnification, but you can push this if you have a wide field of view eyepiece. The starfield you’ll see will doubtless take your breath away.
Take your time to study the brightest stars in the group, all nine of which fit inside a 1° field of view, as shown below in blue. In between these stars, can you spy the nebulosity wrapping itself around some of the main characters?
Merope is the star with the brightest nebula twisting around it but you should also see tendrils of ghostly gases around Alcyone, Maia, and Electra.
The Pleiades is one of the most famous sights in the winter night sky, and with good reason: it is beautiful!
Whether you try and pick out as many stars as you can with the naked eye, or you zoom in for more detail with binoculars or a telescope, you will be awestruck by the beauty of this cluster.
Written by Adam Kirk