[Lvas] Monthly Observer's Challenge - M-13

Mon Jun 29 21:34:26 PDT 2009

MONTHLY OBSERVER’S CHALLENGE
Las Vegas Astronomical Society

Compiled by:
Roger Ivester, Boiling Springs, North Carolina
&
Fred Rayworth, Las Vegas, Nevada

June 2009
M-13 and The Propeller

Introduction
The purpose of the observer’s challenge is to encourage the pursuit of visual observing.  It is open to everyone that is interested, and if you are able to contribute notes, drawings, or photographs, we will be happy to include them in our monthly summary.  Observing is not only a pleasure, but an art.  With the main focus of amateur astronomy on astrophotography, many times people tend to forget how it was in the days before cameras, clock drives, and GOTO.  Astronomy depended on what was seen through the eyepiece.  Not only did it satisfy an innate curiosity, but it allowed the first astronomers to discover the beauty and the wonderment of the night sky.
Before photography, all observations depended on what the astronomer saw in the eyepiece, and how they recorded their observations.  This was done through notes and drawings and that is the tradition we are stressing in the observers challenge.  By combining our visual observations with our drawings, and sometimes, astrophotography (from those with the equipment and talent to do so), we get a unique understanding of what it is like to look through an eyepiece, and to see what is really there.  The hope is that you will read through these notes and become inspired to take more time at the eyepiece studying each object, and looking for those subtle details that you might never have noticed before.  Each new discovery increases one’s appreciation of the skies above us.  It is our firm belief that careful observing can improve your visual acuity to a much higher level that just might allow you to add inches to your telescope.  Please consider this at your next observing session, as you can learn to make details jump out.  It is also a thrill to point out details a new observer wouldn’t even know to look for in that very faint galaxy, star cluster, nebula, or planet.

M-13

M-13, the Great Cluster in Hercules, is an easy target for everything from binoculars to the largest backyard telescopes.  It is easy to spot, even in a finder as a fuzzy blob against a dark background.  On good nights, you may even be able to make it out with the naked eye.  If you do not know your way around the sky, it is well marked in the star charts found in Sky & Telescope and Astronomy magazines.  Just look at the summer charts, and you will see it in the “body” of Hercules.
The challenge is to see more than just a fuzzy blob.  There are a few features noted by observers over the years, starting with Lord Rosse back in the 1700’s (see Lord Rosse M13.jpg).  He noticed spider arms going out from the main body of the cluster, and also three dark lanes in the shape of a “Propeller”.
Walter Scott Houston presented this challenge in "Deep-Sky Wonder's" in Sky & Telescope, July 1953.
In 1980 John Bortle saw the lanes with his 12.5-inch reflector at 176X.  Dennis di Cicco, at Stellafane in 1981, was surprised by how easily the lanes were seen with the 12-inch f/17 Porter turret telescope at about 180X.  However, even knowing their orientation and appearance, he was unable to see them at 95X with a 12-inch that was set up nearby.  Sighting the lanes seems to depend upon a careful balance of aperture and magnification.
Both John Bortle and Dennis di Cicco commented on the importance of magnification.  Most observers note that they appear best at a magnification of about 200X.  Information compiled from "Deep-Sky Wonders" by Walter Scott Houston, selections and commentary by Stephen James O'Meara; Sky Publishing Corporation, Cambridge, Massachusetts 1999.
This month’s observing challenge includes notes and drawings from Roger Ivester, Fred Rayworth, Steve Davis, Ryan Rogers, and Jason Snyder.  Also included are photos from Rob Lambert, Frank Barrett, Jason Snyder, and Jim Gianoulakis.

Observations/Drawings/Photos

Roger Ivester (see Rogers Pictures 003.jpg):  Observer from North Carolina
Roger saw the propeller for the first time using a 12-inch reflector at 196X.  He found it very subtle and averted vision considerably improved the definition of the three dark lanes.  His location was at a dark site in the South Mountains of North Carolina, only 20 minutes N of Boiling Springs, N.C.
The conditions were very good with temperatures near 50° and very low humidity.  The naked-eye limiting magnitude was 6.5 at the zenith.  Roger was with friend and fellow observer Steve Davis, who also saw the propeller for the first time.  His sketch of the propeller using the 12-inch clearly shows all three of the dark lanes.  Both were very surprised that they had never seen the propeller before (see Rogers M13 With 12 Inch.jpg).
Roger also observed M-13 and the propeller from his backyard within the city limits of Boiling Springs, N.C. using his 10-inch reflector at 200X.  Warmer temperatures, higher humidity and ambient lighting reduced the naked eye limiting magnitude to a 5 or maybe slightly less, but the stability of the atmosphere and seeing were excellent.  He was able to use 266X, obtaining excellent resolution, but no propeller.  A magnification of 200X seemed to bring out the dark lanes.  Both Bortle and di Cicco had mentioned this in 1980 and 1981 respectively, noting their success with a magnification of near 200X.
Roger had extreme difficulty seeing the propeller from his backyard.  He could only glimpse the two inner lanes using averted vision, and could not hold them constantly.  He was unable to see the outermost lane that extends out from the cluster.  It is of Roger’s opinion that if he had observed from a dark site, he would have been able to see all three of the dark lanes using his 10-inch (see Rogers M13 With 10 Inch.jpg).

Fred Rayworth (see Fred At Sawmill.jpg):  Observer from Nevada
He was not able to get out in June, but got a good representation of M-13 in mid May. He used a Meade 16-inch, f/4.5 LightBridge.  His eyepieces were an Orion Q-70 26mm (70X), a borrowed Nagler 20mm type 5 (91X), and an 18mm Bertele (101.5X).  He observed from Sawmill Trailhead, Lee Canyon, Nevada (7400 feet).
            On May 16, 2009 at Sawmill Trailhead, despite the much higher altitude, the sky was not very dark and an annoying cold wind hampered his observations by making his eye water constantly as he tried to look through the eyepiece.
He started with 70X, and M-13 was just a fuzz ball with a few individual stars and the spider arms (which are not the same as the propeller).  He then tried the Nagler 20mm at 91X but saw no significant difference, except the field was flatter.  Then he boosted the magnification to 140X with the 26mm and a Barlow, and saw the propeller flashing in and out.  When he increased magnification to 203X by using the 18mm Bertele and Barlow, he saw the propeller better, but had trouble keeping it in the field because of the gusty winds, blurring in and out of focus, and his eye watering.  Another observer, Ryan Rogers, looked at it and Fred asked him to describe what he saw.  Ryan also saw the propeller.  Fred then knocked the magnification back down to 140X and had no trouble seeing it from then on, though it was still a bit erratic because of the sky conditions.  He did a drawing of what he saw at 140X (see Freds M13.jpg).

Rob Lambert:  Observer from Nevada
Rob observed from Kaibab Lodge, at the entrance to the Grand Canyon.  The conditions were not anywhere near perfect.  He had to look between some clouds and it was also quite breezy.  He couldn't get consecutive image captures because the wind was strong enough to rock the scope with the Mallincam on it.  After showing about 20 people some of the night sky wonders earlier in the evening, he was able to view M-13.  Unfortunately, since it was at the zenith, he couldn't use the LX200 with its Alt/Az mount.  At zenith, the optical path with an extension tube and the Mallincam was too long to go between the arms of the scope to point straight up.  Instead, he had to use only the ST120, but reduced the focal reduction to get a larger image (see Robs M13.jpg).
Even with the less than ideal conditions, he was able to see the propeller.  The two blades extending into the cluster were obviously more prominent, but the one extending outward was definitely there, just not as long in length as the other two.  The core was still somewhat washed out, so the next time, he will turn the gain down even more.  He was somewhat embarrassed to send a representative image, since with the wind, the focus was horrible.  However, it gives everyone an idea of what he saw on those moments when the wind let up just for a brief moment.
For the first time while observing through the Mallincam, he was able to observe color in the stars not contained in the core.  He noted yellow and bluish-purple stars (clearly visible in the accompanying image).  One should also notice another dark lane on the lower side of the image, opposite the propeller blades that extend into the core.  It reminded him of the "T" that TeleVue uses in their logo.  In the image, it looks like a wide bar with a significant bump left of center.  There are chains of stars extending from the cluster that suggest M13 may have had a more spiral structure in its past.  Without any supporting research, the image suggests the cluster had a counterclockwise spiral.  He was sure it had undergone significant change in its 13-billion year life.

Frank Barrett:  Observer from North Carolina
Frank allowed us to present his outstanding photo of M-13 from his web site Celestial Wonders celestialwonders.com/ (see Franks M13.jpg).  It clearly shows the propeller.  Also note the multi-colored stars.  The image was taken with an Orion 80mm ED, 600mm f/7.5, with an SBIG ST-2000XCM camera and a Losmandy G11 mount, from Gastonia, North Carolina.

Jim Gianoulakis (see Jim Gianoulakis.jpg):  Observer from Nevada
He was in Bryce Canyon National Park, as a volunteer for the astronomy outreach program for the last two weeks, with little access to communication.  It was unseasonably warm and cloudy, but they had a few decent nights.  The skies were magnificent.  It is said the skies there were mag 7.4, and it is striking compared to the light dome of Las Vegas.  He shot an image of M13 between the clouds.  He noted that now that he knows what to look for, he can't help but see the propeller (see Jims M13.jpg).

Jason Snyder:  Observer from Nevada
M-13 was at his zenith and the seeing was fair, with considerable light dome from N. Las Vegas, NV up to about 45 degrees.  He was using his LX200 GPS/8" scope with a 15 mm eyepiece.  There was a light breeze and the temp was around 86 degrees.  He tried using a Parks blue filter to bring out some detail, but switched to a yellow one instead.  He could not pick out the dark lanes or the "propeller". He had to use averted vision to see any stars available because of the light from the city.
He made a drawing of what M-13 looked like with the few stars he could see at 00:00 hrs. (L) (see Jasons M13 Drawing.jpg).  Later in the evening, approx. 01:39 hrs. (L), he took the following pictures.  The first one was taken with a Rebel EOS, XT bulb setting, 20 sec. exposure through Lumicon GEG, through F-10 LX-200 8" scope (see Jasons M13 Photo 1.jpg). The second one was taken with a Cannon, Rebel EOS, XT.  Exposure was a 15 sec. bulb through a Lumicon GEG through F-10 LX-200 8" scope (see Jasons M13 Photo 2.jpg).  The seeing was better, but he moved onto other targets for a brief session.

References

(Submitted by Roger Ivester)

Sky and Telescope Magazine
Deep-Sky Wonders by Walter Scott Houston, Selections and Commentary by Stephen James O’Meara, Sky Publishing Corporation, Cambridge Massachusetts 1999.
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