Messier 52 – the NGC 7654 Open Star Cluster

The location of the Messier 52 open star cluster, located in the direction of the southern constellation Cassiopeia. Credit: Wikisky

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the open star cluster of Messier 52. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is Messier 52, an open star cluster that can seen in proximity to the northern constellation Cassiopeia. Located about 5000 light years from Earth, this star cluster is easily spotted in the night sky because of its association with Cassiopeia’s familiar W-shape. It can viewed with binocular and telescopes, and will appears as a hazy, nebulous patch of light.


Located roughly 5000 light years away, this 35 million year old cluster of stars has around 200 members – one of which is a very peculiar Of star. According to A.K. Pandy (et al), M52 is an interesting cluster in which to study star formation history. As they stated in their 2001 study:

“The colour magnitude diagrams show a large age spread in the ages. Star formation was biased towards relatively higher masses during the early phase of star formation whereas most of the low mass stars of the cluster were formed during the later phase. The star formation seems to have been a gradual process that proceeded sequentially in mass and terminated with the formation of most massive stars.”

The Messier 52 open star cluster. Credit: Wikisky

Indeed, M52 has been very studied for its star structure, including a search for variables. As S.L. Kim (et al), wrote in a 2000 study:

“We have performed a long-term project of CCD photometry of open clusters. Its primary goal is to search for variable stars, in particular short-period (less than a few days) pulsating stars such as Delta Sct, Gamma Dor, and slowly pulsating B-type stars (SPBs). These pulsating stars are recognized as important objects in studying stellar structure and testing evolution theory of intermediate-mass main sequence stars. Thus these clusters are ideal targets to investigate whether Gamma Dor type variability occurs in old open clusters or not.”

And it’s not just the structure they’re looking at – but the time frame in which they formed. As Anil K. Pandey wrote in her 2001 study:

“The distribution of stars in NGC 7654 indicates that the star formation within the cluster is not coeval and has an age spread -50 Myr. We found that star formation took place sequentially in the sense that low mass stars formed first. The star formation history in NGC 7654 supports the conventional picture of star formation in cluster where ‘low mass stars’ form first and star formation continues over a long period of time. The star formation within the cluster terminates with the formation of most massive stars in the cluster.”

History of Observation:

M52 was an original discovery of Charles Messier, captured on the night of September 7th, 1774. As he wrote in his notes at the time:

“Cluster of very small stars, mingled with nebulosity, which can be seen only with an achromatic telescope. It was when he observed the Comet which appeared in this year that M. Messier saw this cluster, which was close to the comet on the 7th of September 1774; it is below the star d Cassiopeiae: that star was used to determine both the cluster of stars and the comet.”

Atlas Image mosaic of Messier 52, as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/UPAC/Caltech/NASA/NSF

Sir William Herschel would also observe M52, but he would keep his notes private. As he wrote on August 29th, 1873:

“All resolved into innumerable small stars without any suspicion of nebulosity. 7 ft., 57. In the sweeper, 30, shews nebulosity, the stars being too obscure to be distinguished with its light tho’ considerable.” and again on December 23, 1805: “Review. Large 10 feet. This is a cluster of pretty condensed stars of different sizes. It is situated in a very rich part of the heavens and can hardly be called insulated, it may only be a very condensed part of the Milky Way which is here much divided and scattered. It is however so far drawn together with some accumulation that it may be called a cluster of the third order.”

Herschel’s son John would also add it to the General Catalog a few years later with less descriptive narrative, but it was Admiral Smyth who described M52’s beauty best when he said:

“An irregular cluster of stars between the head of Cepheus and his daughter’s throne; it lies north-west-by-west of Beta Cassiopeiae, and one third of the way towards Alpha Cephei. This object assumes somewhat of a triangular form, with an orange-tinted 8th-mag star at its vertex, giving it the resemblance of a bird with outspread wings. It is preceded by two stars of 7th and 8th magnitudes, and followed by another of similar brightness; and the field is one of singular beauty under a moderate magnifying power. While these were under examination, one of those bodies called falling stars passed through the outliers. This phenomenon was so unexpected and sudden as to preclude attention to it; but it appeared to be followed by a train of glittering and very minute spangles.”

May it glitter and spangle for you!

The location of Messier 52 in proximity to the constellation Cassiopeia. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 52:

In the rich star cluster fields of Cassiopeia, M52 is distinctive for its size and brightness. It’s not hard to find! Begin by identifying the W-shape of Cassiopeia and focus on its two brightest stars – Alpha and Beta. Because this constellation is circumpolar, remembering to look at the side that has the brightest stars or the steepest angle, will help you remember how to find this great open cluster. Now, just draw a mental line between Alpha, the lower star, and Beta, the upper.

Extend that line into space about the same distance and aim your binoculars or finderscope there. In binoculars M52 will show clearly as a beginning to resolve star cloud and a hazy patch in a telescope finderscope. Even the smallest of telescopes can expect resolution from this multi-magnitude beauty and the more aperture you apply, the more stars you will see. M52 is well suited to urban or light polluted skies and stands up well to fairly moonlit conditions and hazy skies.

Object Name: Messier 52
Alternative Designations: M52, NGC 7654
Object Type: Open Galactic Star Cluster
Constellation: Cassiopeia
Right Ascension: 23 : 24.2 (h:m)
Declination: +61 : 35 (deg:m)
Distance: 5.0 (kly)
Visual Brightness: 7.3 (mag)
Apparent Dimension: 13.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier ObjectsM1 – The Crab Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.


How Big Is The Big Dipper?

How Big Is The Big Dipper?

The Big Dipper is big. Come on, it’s right there in the name. But how big is the Big Dipper if you could see it from all angles?

Ask someone to name a constellation and they’ll usually say the Big Dipper. Anyone living in the Northern hemisphere who can draw a spoon generally can recognize it in the sky.

I am about to shake the foundations of your reality with a level of pedantry that at bare minimum should earn me a solid shaking and possibly even a face punch or two. The Big Dipper is not, and never will be a constellation.

It’s an asterism, a familiar pattern of stars in the sky. There are 88 constellations, and the Big Dipper isn’t one of them. It’s a part of the constellation of Ursa Major. In fact, the handle of your familiar spoon is actually the tail of the great bear.

Now that I’ve lulled you to sleep with some painfully uninteresting specifics, which you can bust out to make yourself unpopular at your AV Club pop and chip parties whenever someone refers to the “Big D” as a constellation. I strongly suggest whatever it is you tell them, you start off with *ACTUALLY….*

And now that you’ve made it this far, I shall reward you with what you’re seeking. Just how big is that Big Dipper? There are a couple of ways to skin this bear’s tail. We can say its size relative to the amount of sky real estate it occupies, or we can do the end to end Kessel run.

This chart shows the constellation of Carina (The Keel) and includes all the stars that can be seen with the unaided eye on a clear and dark night. This region of the sky includes some of the brightest star formation regions in the Milky Way. The location of the distant, but very bright and compact, open star cluster NGC 3603 is marked. This object is not spectacular in small telescopes, appearing as just a tight clump of stars surrounded by faint nebulosity. Credit: ESO
This chart shows the constellation of Carina (The Keel) and includes all the stars that can be seen with the unaided eye on a clear and dark night. Credit: ESO

You might be surprised to know how much of the sky it takes up. Astronomers measure the sky in degrees. 360 degrees takes you all the way around the sky, and our Moon measures half a degree across.

Dubhe and Merak are the pointer stars in the Big Dipper. You could put 11 full Moons side to side in the gap between them. And about 40 full Moons from bottom corner of the Dipper to the end of its handle. So, the Big Dipper measures about 20 degrees.

Here are some easy ways to measure sizes. Your pinkie nail, held at arm’s length is half a degree. 3 fingers is 5 degrees, your fist is 10 degrees. Rocking out with devil horns are 15 degrees and hang loose or the inspector gadget phone is 25 degrees.

Trekkers and Trekkies may prefer to use the Vulcan live long and prosper measurement, which is about the same number of degrees you are from getting a romantic companion.

Big Dipper Past. Credit: Alexander Meleg
Big Dipper Past. Credit: Alexander Meleg

So, stem to stern, how big is our giant celestial ladle? I know you know those things aren’t in anything resembling a straight line. Some of the stars are closer, and some of the stars are further out. If you could make a box that completely surrounded them, how big would it be?

The closest star in the asterism is Megrez at 58 light years. and the most distant is Dubhe at 124 light-years. And yet, they all look roughly the same brightness. This means that Dubhe is a much brighter star than Megrez, and it’s just further away. Because these stars are moving in the sky what we see as a Big Dipper today didn’t always look this way. 150,000 years ago, the Big Dipper looked like this (above).

Big Dipper Future. Credit: Alexander Meleg
Big Dipper Future. Credit: Alexander Meleg

And in 150,000 years from now it’ll look like this (left). Less dipper, more plow-like. Or maybe a shoe form? Shoes are kind of like ladles, right? Super gross, terribly unhygenic ladles.

Our brains keep from exploding by being pattern making machines. We see collections of stars in the sky and turn them into shapes. But it’s all just a matter of perspective. You’ve got to be right here and now to see the sky we do. Unless you’re looking for a giant “W” in which case you’ll always find one of those. It may not be the constellation Cassiopeia, but it’ll still be a pattern in the stars.

What’s your favorite asterism? Tell us in the comments below.

ISS and Cassiopeia by Adrian New

Astrophoto: ISS and Cassiopeia by Adrian New
ISS and Cassiopeia. Credit: Adrian New

On the morning of September 21, 2011, the International Space Station made a beautiful pass over San Antonio, Texas through the constellation of Cassiopeia. The pass was caught by Adrian New using his Nikon D200 camera and 18-70mm lens. The camera was set at ISO 200 and 30 second exposure.

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