Our challenge for August was M2, the Globular Cluster in Aquarius. The specific challenge features focused on this magnificent globular's shadows. From Stephen James O'Meara's "The Messier Objects", the cluster's outer envelope appears to have a north-south asymmetry. Shadows seemed to blow out from the center with the streams of stars, forming spidery arms. One particular shadow we were hunting slices through the northeast section of the outer halo and runs northwest to southeast. To help you find this particular shadow or dark lane, locate the obviously brighter 10th-magnitude star out to the northeast. The dark lane of our challenge lies halfway between this star and the cluster's center. O'Meara's sketch of the cluster hints at our challenge feature (see below). For imagers, you may have to experiment with different exposures to capture the dark lane. You'll have to find the balance of exposure and resolution to observe this elusive feature.

 

Interactive Sky Map- M02

Other challenge features included locating the yellow and red-giant stars within the cluster. In the future, if you have the opportunity to observe the cluster over a couple of weeks, try to locate a prominent variable star located on the eastern edge of the cluster, just slightly north of center. The variable fluctuates between 12.5 and 14-mag within about 11 days. This variable, known as Chevremont's Variable, is said to be within the range of a good 2-inch scope.

Below are the notes, sketches, and photos of participants in the August 2009 Challenge:

M2 Globular Cluster 

Compiled by:

Roger Ivester, Boiling Springs, North Carolina

and

Fred Rayworth, Las Vegas, Nevada

M-2 is the famous globular cluster located in Aquarius, one of the brighter Messier Objects, and is an easy object to see in almost any telescope. This rich cluster is often seen as smooth and fairly round. Many people never notice the additional feature that cn be revealed with careful observation and the correct magnification. One of the most interesting features from a visual basis is a curving dark lane crossing the northeast section of this very dense cluster. Many observers find this lane to be very difficult, regardless of the sie scope used.

In the Observing Handbook and Catalogue of Deep-Sky Objects, by Brian Skiff and Christian Luginbuhl: "in 25cm, a well-resolved mass of stars is visible at 200X, rising to a broad, bright center. The cluster is well resolved in 30cm, with a smooth texture due to the uniform magnitude of the stars."

Roger has been fortunate to know both Tom Lorenzin and James Mullaney personnally, and feels honored to be able to call both of these highly skilled observers and book authors friends. He has learned much from their writings over the past 20 years.

James Mullaney, Celestial Harvest, M-2: "Small glass shows a granulated aspect, the precursor of resolution. Not resolved in a 4-inch."

Tom Lorenzin, 1000+ The Amateur Astronomer's Field Guide to Deep-Sky Observing, M-2: "6-mag, 7' diameter; bright and round; just resolved at 100X, 13-mag dimmer members, 11-mag star 2' due N of core, 5' NNW of core." 

John Mallax and Evered Kreimer, The Messier Album, M-2: "4-inch Unitron Refractor. The Mallas 4-inch refractor does not resolve the cluster, except for a few bright members across the nebulous image. Visually, the most unusual feature is the dark curving lane that crosses the northeast corner of the cluster. Thought first to be an illusion in the 4-inch, this feature can also be detected in the photograph by Kreimer (12.5-inch f/7Cave reflector). 

This observing challenge includes notes and drawings from Roger Ivester, Fred Rayworth, and Jason Snyder; notes only from Tony Labude; images and notes from Rob Lambert; and photos from Frank Barrett, Jim Gianoulakis, and Ryland Ogle. 

Observation Notes, Sketches, and Images

Roger Ivester - LVAS member from North Carolina

M-2 is a bright 6.4-magnitude globular cluster that is unresolved in the 4-inch refractor. When using a 16mm University Optics Konig eyepiece and a 2.8X UO Klee for a magnification of 175X, the texture of the cluster became very granular, but without resolution. The cluster was very bright and well concentrated with a brighter middle.

A few of the brighter stars could be seen around the outer perimeter and there was the appearance of a faint halo surrounding the cluster.

 

The curving dark lane, as described by John Mallas in the Messier Album using a 4-inch Unitron refractor, proved to be difficult indeed. It required averted vision with the 4-inch at 175X and was fleeting, at best. The dark lane could not be held constantly, but during moments of steady viewing, it was an amazing sight, almost appearing surreal. It is interesting to note that Mallas himself thought it initially to be an illusion.

After countless observations of this cluster over the past 20 years, I have only observed the dark lane once, despite using a variety of telescopes, including a 10-inch reflector.

Walter Scott Houston reported seeing M-2 with the naked eye. He saw the cluster from Kansas, Missouri, Arizona, and Louisiana, but never mentioned seeing the dark lane with either the 4-inch Clark refractor or his 10-inch reflector.

Fred Rayworth - LVAS member from Las Vegas

Because of a park ranger, I never got a chance to observe M-2 for this challenge; however, going back over my notes, I've never picked out the dark lane. My most common observation, besides a soft milky glow, is a brighter foreground star within the cluster that is off to one side.

Rob Lambert - LVAS member from Las Vegas 

In observing M-2 for this month's challenge, I used my Mallicam at integration settings of 2, 7, 14, and 28 seconds. The 56-second integrations/exposures washed out too much of the globular's core to be useful. At each of these integration settings, I was able to locate the curving dark lane described in the challenge. As can be seen in all of the provided images, the dark lane is just over half-way between the brighter star on the northeast (left) edge of the cluster and the core. In these images, it looks like a parenthesis "(" left of the core, that curves back toward the core. These images are flipped horizontally and vertically. in orientation since they were captured with my 10-inch LX200GPS (SCT). North should be to the bottom left corner of the images, and East should be the upper left corner.  In the 7 and 14-second images, there is a smaller dark lane that resembles a reversed letter "C" between the curving dark lane and the core. At longer integrations/exposures, the smaller dark lane gets washed out.

2-second Mallincam Image                                                                7-second Mallincam Image 

14-second Mallincam Image                                                             28-second Mallincam Image 

These particular images seem to give the impression that the cluster is moving toward the East like a comet, trailing stars in several chains out to the West. Many of the stars in these chains and many others around the outer periphery of the cluster can be individually resolved and are red and yellow in color. I didn't have the opportunity to decrease the focal reduction to increase the magnification of the cluster. I hope to observe it again, on my next outings to Cathedral Gorge and Death Valley, at higher magnification so I can better identify the red and yellow giants that occupy the outer regions. At some time in the future, I hope to be able to identify the variable star mentioned in the challenge, since I didn't have an opportunity to view the cluster over a two week period and attempt to identify it.

Although not as large and spectacular as the Hercules Cluster, M-2 is interesting in its own right, with its dark lanes, chains of stars, and colorful stars. Look for updates to my M-2 observations in the near future.

Ryland Ogle - LVAS Member from Las Vegas

Ryland provided this image of M-2 captured with his new Mallincam.