Test your eyes on M45 aka Pleiades or Seven Sisters

Test your eyes on M45 aka Pleiades or Seven Sisters

By Chris Fellows, Serenity Mobile Observatory

As winter approaches, a beautiful star cluster called the Pleiades, or the Seven Sisters, is coming into view in the early eastern night sky. This open star cluster containing middle-aged, hot B-type stars located in the constellation of Taurus, is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky.

M45, the Pleiades star cluster. Photo: NASA

M45 can be easily spotted even under poor viewing conditions from late summer to early spring. The cluster has a “dipper” shape, as you can see in the photo, and I have heard people call it the “Little Dipper.” This is incorrect, as the Little Dipper (Ursa Minor) is near the Big Dipper (Ursa Major) in the northern sky. The North Star, Polaris, is the last star in the “handle” of the Little Dipper.

Most people can spot the five brightest members of this cluster, but exceptional observers can pick out many more. Some accounts tout as many as 20 or more naked-eye observations in this cluster. I am a bit skeptical of those claims since none of them appear prior to Galileo’s description of the cluster through his telescope. In a magnified view the Pleiades contains about 1000 stars: It is 13 light-years across, and about 444 light-years from earth. [Editor: Put simply, a light-year is the distance that light travels in one year.] Scientists now believe that the nebulosity [cloudiness] associated with this cluster isn’t the cluster’s nursery nebula, as originally thought, but simply a patch of gas and dust the cluster is currently moving through. Wherever it comes from, the nebula makes this star cluster a very beautiful object in long-exposure photography.

Star map to Pleiades. Click here for larger image.

This time of year is the best time for observing the Pleiades. If you look east at around 7:30 p.m. Central/Mountain time, and about halfway up between the horizon and the zenith, you won’t be able to miss this star cluster. Unlike everything else in the sky, this group of stars glows brightly with a halo of bluish light. It is my favorite object to demonstrate averted vision on. Step outside and try this, it is really quite surprising if you haven’t seen it with your own eyes. Use the description above or this star map to locate the Pleiades. Now, look slightly away but concentrate on the cluster. Pop! Now look back, the light will diminish, now slightly away again – pop! It’s pretty cool, and once you have seen it you won’t be able to un-see it.

Galileo Galilei’s 1610 sketch of the Pleiades; from Wikipedia

The Pleiades have been known since antiquity and have many legends associated with them. They are even mentioned several times in the Christian Bible. The earliest known depiction of the Pleiades is a North German Bronze Age artifact known as the Nebra sky disk, dated to approximately 1600 B.C. Galileo Galilei was the first astronomer to view the cluster through a telescope. He is responsible for the discovery that the cluster contains many more stars than people thought. Galileo published his observations, including this sketch of the Pleiades, in 1610. Charles Messier measured the position of the cluster and included it as M45 in his now famous catalogue of not-comets, published in 1771.

The Pleiades adds another arrow to your quiver of night sky objects that you can point out to friends and family. It is a very easy binocular target and looks fantastic through a modest pair of 8X50 or even smaller. Get yourself and your people out there and look up! We live in an amazing and awe-inspiring universe – It’s worth taking a look at.

Clear Skies,
Chris Fellows, Serenity Mobile Observatory

Find Chris on Facebook (or, if you’re lucky, at your campground). (Editor: Check out his amazing photos on his Facebook page!)

 ##RVT823 

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