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Finally Nailed Messier 91 & 98

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#1 Richard1949

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Posted 13 May 2012 - 06:06 PM

I thought I would never nail these two. But last night the sky had top notch transparency where I live. (5/5 on ClearSky chart) So I tried again. Both were about 60 degrees elevation, and I used the 8" with 51x. At first I couldn't see anything, so I looked at Mars and Saturn for awhile and looked at some other DSO's. After about half an hour I went back to M91 and 98 and looked and looked. Finally each one popped into view with averted vision,,,then pop out again, and back in. Barely visible. Going up to 75x helped a little. Wow, were they difficult. I`m so used to most of the other Messier objects being so bright. A lot of the Hershel 400 objects are easier to spot than M91 and 98. :jump:

#2 IVM

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Posted 14 May 2012 - 12:22 AM

Congratulations. Messier commented on the extreme faintness of these objects, even though he knew where to look because Mechain had discovered them from a darker location with a larger telescope. I first saw both from the legendary Star Hill Inn (good green zone) with the 24-inch Ritchey-Chretien (the retired professional… does anyone know what became of it?). I do not have any clear recollection of their appearance on that night, though. Most likely I saw no detail because even in the scope that size it should be subtle and I did not give it enough time. Later I saw them with my 4” from the blue zone and found them faint and featureless aside perhaps from M98’s elongation. I have now almost completed the (first round of) comparatively careful re-observation of the non-elliptical Messier galaxies, and M98 was one of the three objects I observed last week. The transcript and sketch from my field journal follow. The Messier galaxies offer a wealth of detail, but the details require effort to see, at least for me, both in terms of actual observing and logistically in terms of getting a large enough scope to a dark enough site.

Cherry Springs [blue zone, elevation 2400 ft]. 16” [f/4.5]. Front with showers passed by astronomical twilight. 10 degrees C. Above average and 55% according to Clear Sky Clock, but both transparency and humidity seem worse. 21.6-21.7 SQM-L. Ethos 13 mm and Pentax 8-24.

Companion NGC 4186. Diameter as the distance between the bright star in the group of 3 and the one next to it, slightly elongated in the direction of the bright star. Companion UGC 7223 invisible (“X” on the sketch).

M98 is overall brighter, and is looking wider to the NW than SE. Bright starlike nucleus. Overall appearance crab-like at 8 and 13 mm [225 and 138x]. The dark gap NW of nucleus is pronounced and deeply invaginated from N. In comparison the gap SE of nucleus is only pronounced near the nucleus; farther away to the SE it looks rather “filled”. The SE enhancement is more parallel to the long axis; NW one is more orthogonal. SE tip beyond the enhancement looks pointed; NW one broad. NW enhancement is farther away from nucleus than SE one. Observation 00:00-00:50.

EDIT: The appearance is caused primarily by the dust clouds along the N edge which is nearer to us. The "object" on the lower right is not Hanny's Voorwerp or anything uncharted. It is a flower print on the page of the notebook I borrowed from my SO once upon a time and never returned.

Attached Thumbnails

  • 5221231-M98 2012-05-10 processed.jpg


#3 IVM

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Posted 14 May 2012 - 03:12 PM

Here is the sketch of M91 that I made last month with my 12" Orion XT Classic Dob. The CSC forecast for Cherry Springs that night was "transparent" and 55% humidity, 0 deg C. The observation was from 03:25 till astronomical twilight at 04:05, and the sketch is the composite of the views obtained with the 8-24 mm Pentax zoom (63-188x).

Attached Thumbnails

  • 5222243-M91 2012-04-28 IVM 12-inch XT Classic.jpg


#4 Richard1949

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Posted 15 May 2012 - 07:14 AM

Good sketch.


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