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All,<BR>
<BR>
Throughout the years, I've seen M-13 with a variety of visual differences. Even with my old 8" home built reflector, I saw spider arms going out from the center core. These arms became even more distinct with my next 16" homebuilt scope. These are not to be confused with the dark propeller, as these are bright arms of stars concentrated more in lanes going out from the core, rather than a solid mass of stars as it is in the center. I may have seen the propeller before and noted the dark "blotchy" area to the side of the core, but never recorded it as a propeller shape until recently, when it pretty much slapped me in the face at 140X. There is quite a bit more to see than just a fuzzy clump of stars!<BR>
<BR>
Fred<BR>
<BR> <BR>
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From: drivester@hotmail.com<BR>To: lvas@lvlug.org<BR>Date: Wed, 27 May 2009 01:11:54 +0000<BR>Subject: [Lvas] FW: June Observer's Challenge "Supplemental"<BR><BR>
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From: drivester@hotmail.com<BR>To: lvas@lvlug.org<BR>Date: Wed, 27 May 2009 01:07:34 +0000<BR>Subject: [Lvas] June Observer's Challenge "Supplemental"<BR><BR>
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All,<BR> <BR>I was looking for the latest <EM>Deep-Sky Wonders </EM>article by Walter Scott Houston concerning the finest globular cluster of the northern sky, M-13 and the illusive propeller. <BR> <BR>August 1992 <EM>Sky & Telescope</EM>, <EM>Deep-Sky Wonders, </EM>by Walter Scott Houston, page 225. <BR> <BR>Recently, an obscure feature of M-13 has become a visual quest for amateurs. During the middle of the last century, observers using Lord Rosse's large reflector in Ireland noted three dark lanes radiating propeller-like from a common point southeast of the cluster's center. These lanes were well enough known that the Rev. T.W. Webb mentioned their visibility with a 9-inch reflector in his classic, late-19th-century observing guide <EM>Celestial Objects for Common Telescopes. </EM><BR><EM></EM> <BR>I have the two volume set by the Rev. T.W. Webb. Volume Two: The Stars, written 1859, and revised by Rev. T.E. Espin in 1917. <EM>The Dover edition</EM>, first published in 1962, is a revised and enlarged republication of the sixth edition of the work written by the Rev. T.W. Webb. <BR> <BR>I have always found this most historical book to be invaluable as a reference source. This was one of the most used and coveted deep-sky reference books for over 100 years. <BR> <BR><EM>Celestial Objects for Common Telescopes</EM>: Volume two: The Stars, page 143.<BR> <BR>h. describes "hairy-looking curvilinear branches" well seen with 8-inch "With" mirror; E. of Rosse, who noticed this spiral tendency, detected also three dark "lanes" or rifts in the interior, beautifully seen by Buffham with 9-inch. "With" mirror. I have also perceived them.<BR> <BR>Our "Observers Challenge" for June will be M-13. We will be looking for the illusive "propeller" within M-13. Three dark lanes radiating from the central region. See my sketch of Lord Rosse's sketch of about 1850 from Ireland.<BR> <BR>WSH brought presented this challenge in "Deep-Sky Wonder's" in Sky & Telescope July 1953. <BR> <BR>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. <BR>Both 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 from <EM>"Deep-Sky Wonders" </EM>by Walter Scott Houston, selections and commentary by Stephen James O'Meara; Sky Publishing Corporation Cambridge, Massachusetts 1999. <BR> <BR>Roger Ivester<BR> <BR><BR><FONT face=Verdana size=4></FONT> <BR> <BR><BR>
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