Date: May 13, 2009
Title: Messier’s First Unique Find – Globular Cluster M3
Podcaster: RapidEye Observatory
Organization: RapidEye Observatory
Description: A brief overview of Globular Clusters, discuss Charles Messier and his list (brief), and observing Messier’s first unique find, M3.
Bio: I’ve been captivated by astronomy ever since I was a kid, living in NW Colorado where the Milky Way was bright enough to read by. I can be found most clear nights in my pasture with either my 4.5″ Dob, 10″ Dob, or my binoculars.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Valcato Hosting. To celebrate the International Year of Astronomy, Valcato Hosting is offering one year of free web hosting for any and all astronomy web sites! All accounts come with tools to make it easy to set up blogs, forums, photo galleries, and more. Sign up now, and start sharing your astronomy experiences with the rest of the world! For more information, please visit www.valcato.com/iya
Transcript:
After studying the object in his telescope carefully, the observer records an entry into his logbook “Nebula discovered between Bootes and one of Hevelius’s Hunting Dogs. It does not contain any stars, the center is bright, and its light decreases imperceptibly; it is circular. Under a good sky it can be seen with a one-foot telescope. It is plotted on the chart of the comet observed in 1779, Memoires de l’Academie for that year.” The date was May 3rd, 1764 and the “observer” was none other than “the Comet Ferret” himself Charles Messier.
It wasn’t the first “nebula” Messier had recorded. Several years earlier in 1758 he had found a “Nebula above the southern horn of Taurus, which does not contain any stars. Its light is whitish and elongated like a candle flame.” He had found that particular comet impostor while observing the comet of 1758. But this first Nebula had already been observed and charted by English astronomer Dr. Bevis 27 yrs earlier. We know now it as M1, or the Crab Nebula.
It also wasn’t the first globular cluster Messier had recorded; however, he didn’t know that at the time. Two years after recording his first “nebula” he found a “Nebula without a star in the head of Aquarius. The center is bright, surrounded by circular luminosity; it resembles the beautiful nebula that lies between the bow and head of Sagittarius.” He found this particular comet impostor while sweeping for a comet in 1760. This nebula had also been previously recorded by fellow French astronomer Jean-Dominique Maraldi 14 years earlier. We now know this as M2, one of the Fall’s finest Globular Clusters.
But it wasn’t until that night in 1764 that Messier recorded his first unique non-comet object. He didn’t realize at the time, but he was beginning to create a catalog of some of the northern hemispheres most impressive and beautiful deep sky objects, or DSO’s for short. Depending on who you listen to that list currently stands at 109 or 110 objects (a topic for another podcast). Many were found by his assistant Pierre Mechain, while others were added later through historical reviews of his notes. It contains some of the best in class objects for each of the different DSO’s amateur observers hunt for today which is why completing the Messier list is typically one of the first tasks undertaken by most amateurs and serves as the gateway to more difficult and challenging lists.
While Messier was very competitive in his searches for comets, his list of “embarrassing objects” where just that: things that might be mistaken for a comet through their primitive telescopes although they didn’t move across the sky like a comet – they were static that interfered with his hunt. He openly acknowledged Bevis and Maraldi’s earlier observations of M1 and M2 and at the time didn’t appear to be in competition with anyone to find the most nebulas. No, his passion and claim to fame was in finding comets, of which he found plenty. He is credited with finding 13 of his own, co-discoverer on 7 more.
Messier had no way of knowing it because he did not have sufficient optics to observe it, but Messier’s Nebula without any Stars is actually a globular cluster that is made up of approximately half a million stars packed into an ball about 180 – 200 light years across. Because the cluster is almost 34,000 light years away, even an object with 500,000 stars only appears as a small dot about magnitude 6, right at the edge of human vision at a dark site. It wasn’t until 1784 that William Herschel and his larger and more capable telescope were able to resolve that 19 arc minute fuzzy ball into individual stars.
Globular clusters are so interesting because they are comprised of hundreds of thousands of stars packed into, galactically speaking, small spheres. All that we’ve studies are about 13 billion years old, close to the age of our own Milky Way Galaxy and universe itself. Other than galaxies themselves, no other DSO’s have that type of durability. Open clusters tend to disperse after tens of millions of year as they orbit around the Milky Way. Planetary Nebulas and Super Nova Remnants rapidly expand and disperse to the intergalactic media, like a ripple from a rock thrown into a large lake. And beautiful emission nebula and reflection nebulas are actually blown apart and scattered by radiation pressure from the very stars that illuminate them. While the stars inside the cluster have moved around within M3 and its location in the Milky Way has moved around, M3 probably looks pretty close to the same now as it did 1 or 2 billion yeas ago.
Most globular clusters are thought to be the central cores of smaller galaxies that were adsorbed and consumed by our bigger Milky Way galaxy. Through the billions of years of orbiting our galaxy, most of the outer stars have been stripped from the smaller galaxies, leaving only the small, tightly packed cores. This would explain why some, like Omega Centauri are thought to contain black holes at their centers.
From a rural location, even in modest light pollution, finding M3 is fairly straight forward and easy. Start by finding Arcturus or Alpha Bootes. It is one of the brightest stars in the spring and summer skies and this time of the year, around 9PM local time, it should be seen halfway up from the horizon in the east. 25 degrees higher in the sky and further north you should be able to pick out Cor Caroli or Alpha Canes Venatici. Draw a line between the two stars and M3 resides about 40% of the way up from Arcturus to Cor Caroli, next to a magnitude 6 star that is easy to see in a pair of binoculars or a small finder scope. From darker skies, there is an even easier way to find M3. If you can see the 3 brightest stars in the constellation Coma Berenices, follow the line created by Beta and Gama approximately the same distance to the east and M3 should be in the FOV of your finder scope. This is a relatively sparse area of the sky and the 6th magnitude star next to M3 really stands out.
Through a finder scope or an average pair of small binoculars, M3 is easily visible as a smaller hazy patch next to that unrelated nearby field star. Like most globular clusters, typical binoculars and finder scopes reveal little detail and no structure – very similar to a small comet without a tail. Its not hard to see why Messier and his relatively low power instruments could confuse this for a comet and similarly, not have any idea of what it was he was looking at.
Although the view gets bigger and brighter through small telescopes like a 60mm or 80mm refractor, it isn’t until you get to the 4″ range at powers above 65X that M3 starts to reveal its nature. At first glance it has a grainy texture to it and with averted vision individual stars around the edge of the cluster pop in and out of view. Pushing the power to closer to 175X
helps to show that indeed, M3 is a small ball of stars, packed so tightly together one is hardly distinguishable from the next.
As is frequently the case in astronomy, bigger is better, and through a 10″ telescope at 175X the view is outstanding. The core is too dense to resolve anything more than a few twinkling points in bright wash of backlight, but as you move out from the center, more and more individual stars are resolved. While M3 is about the same size as its nearby neighbor in Hercules, M13, it isn’t quite as bright and doesn’t have the long arcing loops of stars that make M13 so distinctive at the eyepiece. None the less, several bands of stars and lanes loop lazily across the face of the cluster.
But if the view is outstanding in a 10″ telescope, nothing can prepare you for viewing M3 through a 20″ telescope. At a recent star party here in Central North Carolina, we used a friends 20″ Obsession telescope to show M3 to several hundred boy scouts, most of which were having their first views through a telescope. Several almost fell into the telescope they were so engrossed in the view while others would clutch the ladder they were standing on in order to steady themselves. Most of the scouts that saw Saturn that night for their first time could be heard to say “wow” or “awesome”, but most that looked at M3 through that gigantic telescope were struck mute. The few that tried to actually articulate what they saw would whisper “so many stars”, “diamonds”, or just “beautiful”.
My impressions were similarly impressive: The field of view just explodes with stars to the point that your eye gets lost in the view. Little structure can be seen because there is just too much to take in all at once. The cluster can be resolved all the way to its core and several small hollows pop in and out of view. Could these be the dark spots first reported by Lord Rosse in Ireland using his Leviathan 72-inch telescope in the mid 1800’s?
I don’t pretend to be as dedicated an observer or even in the same league as Lord Rosse, Charles Messier, or William Herschel, but rather, I’m fortunate enough to live in a time where even with our light polluted skies we have access to affordable equipment that would have made professional astronomers of the previous generations green with envy. While I haven’t found any new comets nor do I expect to find any in the future, M3 was also my first original DSO found by myself using my small 4.5″ F/9 Dobsonian Reflector from my yard in Rural NC. The small ghostly glow at 90X hooked me for life: Globular Clusters are still to this day my favorite DSO’s in the sky.
See the show notes at the 365 days of astronomy website for links to reference books and materials used in the creation of this podcast: For if I have seen a little further it is by standing on the shoulders of Giants.
Show notes:
All Sky Map – Chart to find M3:
http://skymaps.com/downloads.html
M3 Details:
http://www.maa.clell.de/Messier/E/m003.html
Deep Sky Companions by Stephen James O’Meara:
http://books.google.com/books?id=jis4evHuuzUC&dq=deep+sky+companions+the+messier+objects&source=bn&ei=MgT_SY6gAZ6xtgeB58mSDA&sa=X&oi=book_result&ct=book-ref-page-link&cad=one-book-with-thumbnail&resnum=4
Atlas of the Messier Objects: Highlights of the Deep Sky by Ronald Stoyan, Stefan Binnewies, Susanne Friedrich, and Klaus-Peter Schroeder
http://books.google.com/books?id=4SiNPQAACAAJ&dq=atlas+of+the+Messier+Object+Highlights+of+the+Deep+Sky&ei=rhf_SZ3mKIKEygSC-tSCCw
More Details on Wolf-Rayet Stars:
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980603a.html
End of podcast:
365 Days of Astronomy
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