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M106, M51, Abell1656 (Coma Cluster)

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#1 Jeff Young

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Posted 26 May 2009 - 02:14 PM

Had to stay up late, waiting for it to get dark. It never quite gets there this time of year, but astronomical twilight is passable for high-altitude targets.

M106 5/26/2009 0:00UT; Pickering 6, NELM 5.5, SQM 20.4

Extremely bright, non-stellar elongated core surrounded by a large elongated disk of asymmetrical brightness. NE arm considerably brighter, but fairly evenly shaded while dimmer, narrower SW arm shows some mottling.

Outer extent of disk not visible. Companion (NGC4248) keeps making me think my eyepiece is dirty.

Posted Image


I was mostly just here to sketch the next one, but I'll include an observation from last year:

M51 Whirlpool 4/30/2008 0:30UT; Pickering 8, NELM 6, SQM 20.9

Absolutely stupendous at 155x: strong E-W flaring apparent in core, with two complete revolutions of the arms, including readily apparent HII regions to the SW in the bridge arm and to the ENE and NE in the other arm. Main flare (to N) in companion direct vision, with secondary (W) and tertiary flares (NW) visible in averted. Tertiary flare quite large but very difficult (perhaps 20% in averted).

Stellar core to both members, but companion's actually appears somewhat brighter. Bottom and top of bridge direct vision; center still averted and somewhat difficult. Beautifully framed at 100x in 39T5 with ink-black background.

Editor's note: the observation was taken under far better conditions than the sketch, so the sketch fails to record the complete set of details from the observation.

Posted Image


Abell1656 Coma Galaxy Cluster 5/26/2009 1:05UT; Pickering 6, NELM 5.5, SQM 20.4

Not the best of conditions for this, but it still reveals a packed field. NGC4889 most obvious, followed by 4898 and 4865, all of which show semi-stellar condensations. NGC4911 was more difficult, with poor condensation, as were 4865, 4908 and IC4051, all showing very poor condensation.

NGC4906 and 4864 showed good condensation, but were difficult to differentiate from stars. GSC1995-01897 was misidentified as a galaxy, while NGC4882, NGC4869, IC3960, NGC4860 and NGC4907 were all misidentified as stars. Total count: 10 sketched, 14 recorded.

I'd love to have this one under darker skies, but it comes around at a bad time of year for 54°N.

Posted Image

I think I might have been able to eek a few more galaxies out of the Coma Cluster, but the dang sun was starting to brighten the horizon by 1:40 (2:40 local time).

Cheers,
-- Jeff.

#2 Bill Barlow

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Posted 26 May 2009 - 02:39 PM

Hi Jeff...

Wow...looks like you had a very good observing session. What telescope did you use to view these galaxies? Fantastic sketches as well.

Bill

#3 Jeff Young

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Posted 26 May 2009 - 02:53 PM

Bill --

They're all done with an APM 16" f/10 Mak-Cass (scope thread). And thanks for the kind words.

Cheers,
-- Jeff.

#4 Jeff Young

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Posted 27 May 2009 - 10:16 AM

Here's an annotated version of the Coma Cluster sketch:

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#5 Bill Barlow

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Posted 27 May 2009 - 10:31 AM

Hi Jeff..

Thanks for the link to your scope. Wow, what a beautiful instrument! I will have to try and find the Coma galaxy group in your sketch. Is it in the constellation Coma Bernice? I have been spending the last few observing sessions viewing some of the galaxies in Leo and Virgo with my Meade 10" ACF SCT. I am also a visual only observer. But if I remember, the galaxies in the Coma cluster are pretty far away..ie 200-300 MLY? They might be too faint for me to see in my slightly light polluted backyard.

Before you ordered the 16" from APM, did you look at the telescopes from Orion Optics in the UK? I thought that they, from what I've read, also produce some very good figured optics. But APM is also world class from what I've heard. Looking forward to future reports/sketches from your observing sessions. Take care.

Bill

#6 Jeff Young

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Posted 27 May 2009 - 04:32 PM

Bill --

Yes, the Coma cluster is right next door to the Virgo supercluster in our sky (not sure where they stand distance-wise).

The Coma cluster members are certainly dimmer than the Messier components and some of the brighter NGC galaxies of the Virgo supercluster, but at least a couple of them should still be within reach or your 10" ACF, and you might be surprised and get a bunch. Let us know how you get on with them....

I did look at Orion Optics, and yes, their optical quality appears very good (although perhaps a bit behind the Intes Micro optics in my APM). Their mechanical quality, though, lags more significantly -- which saves you some coin at the smaller-aperture end of the spectrum, but struck me as counter-productive at the larger-aperture end.

Cheers,
-- Jeff.

#7 Scott K

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Posted 30 May 2009 - 02:49 AM

Jeff,

Thanks for the great report. Because of it, I gave Abell 1656 a shot tonight, and it was well worth it. LOTS of galaxies, just wow! I ended up switching between a 13mm and 7mm Nagler. I didn't try the 31mm, which I sort of regret now. Still, I really enjoyed the feeling of looking out into infinity. (Well, err, for small values of infinity anyway! ;))

#8 Jeff Young

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Posted 30 May 2009 - 08:02 AM

Scott --

Excellent! (I'll bet you bagged a few more of them than I did with that beast of yours.)

Cheers,
-- Jeff.

#9 tatarjj

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Posted 30 May 2009 - 01:56 PM

Hey Jeff,
Nice sketches! I notice that in your annotated version, several "stars" from the first sketch turned out to be galaxies. Was the seeing pretty bad, smearing the stars up, or what factor caused the mistake? Just curious. I've personally had really bad seeing make it difficult to distinguish faint galaxies from stars, but typically its for galaxies smaller and fainter than the Coma Cluster members. I notice you were only using 131X- could that have been the problem? That's seems like a very low power to use for faint galaxy observing. But I guess if you had used higher power, and had been sketching only a single eyepiece field, then you wouldn't have much to sketch if you had gone to higher power!

Anyway, I wish I could sketch like that. Do you have a link/or could explain how you do it?

#10 Bill Barlow

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Posted 30 May 2009 - 03:27 PM

Jeff...

I will try to view Abell 1656 in a few weeks after the moon begins to rise later in the evening/night.

I found out that this super cluster of galaxies is some 250-300 MLY away...way out there! Will let you know if I can at least see the two brightest members NGC 4889 (mag 11.4) and NGC 4874 (mag 11.8) with my Meade 10" ACF SCT.
Clear skies.

Bill

#11 Dave Mitsky

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Posted 30 May 2009 - 03:50 PM

Yes, the Coma cluster is right next door to the Virgo supercluster in our sky (not sure where they stand distance-wise).


One source lists the distance to the Coma Cluster as being 320 million light years, some 5 times farther than the Virgo Cluster.

Using the NED redshift data for Abell 1367 and Abell 1656 results in distances of about 285 and 299 million light years (Ho=74.2).

There's more at http://www.atlasofth...superc/com.html

Dave Mitsky

#12 Jeff Young

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Posted 30 May 2009 - 04:56 PM

John --

I should probably indicate which magnifications I used during a sketch, rather than just the magnifcation which resulted in the field size I drew.

I used 235X and 335X to resolve individual galaxies in the Abell1656 sketch. The biggest problem was that the surface brightness on many of them faded to nothing at 335X, although I suppose that could also be seeing-related. I suspect, though, that that should have been my clue -- any "star" that disappeared with higher magnification was almost certainly a galaxy, right? Even under bad seeing, a star should have stayed visible even if it turned into somewhat of a blob.

I'll have to experiment with that a bit in future observations.

One other thing going on here is that when drawing a galaxy cluster I tend to draw dim sources as stars if I can't tell the difference. Call it vestigial defense against "averted imagination". ;)

Jeremy Perez has some good tutorials on his website (http://www.perezmedia.net/beltofvenus/). I find galaxy clusters one of the easiest things to sketch as there's usually no detail in the individual galaxies -- those with central condensations are simply drawn as stars and then smeared with a blending stump, and those without are smudged in directly with the blending stump.

Cheers,
-- Jeff.

#13 F.Meiresonne

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Posted 30 May 2009 - 06:40 PM

As allways those are great sketches.
That of M51 looks alot just like i see it in the eyepiece.

Indeed unfortunately it does'nt get real dark anymore.
Still i was able to catch hickson 68 en Arp 185 last night from my backyard...

#14 tatarjj

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Posted 30 May 2009 - 08:30 PM

That's odd Jeff. To me, it seems that faint galaxies only get MORE visible as you increase the magnification. In fact at 540X, I can see galaxies that are completely invisible at 140X or 300X. Some brighter galaxies look better at lower powers though. Seeing has to be truely horrendous before it will really affect galaxy observing- so horrendous, I've never seen it that bad. But.. each observer observes differently. I wonder if some other factor is involved?

#15 Scott K

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Posted 30 May 2009 - 11:43 PM

I used 235X and 335X to resolve individual galaxies in the Abell1656 sketch. The biggest problem was that the surface brightness on many of them faded to nothing at 335X, although I suppose that could also be seeing-related. I suspect, though, that that should have been my clue -- any "star" that disappeared with higher magnification was almost certainly a galaxy, right? Even under bad seeing, a star should have stayed visible even if it turned into somewhat of a blob.


Wow, that is weird Jeff. I was observing at 265x (13mm) & 493x (7mm). I can't say whether or not seeing had an affect, because it was quite good for a change last night. I found the 7mm eyepiece worked really well - I could definitely make out a lot more of the members of the cluster. The view with the 13mm was neat - I could observe several galaxies at once, but sometimes there were "hmmm, do I see anything there or not?" type of moments. The 7mm pretty well settled all those questions.

I did see quite a lot of galaxies in this cluster, but it gets fully dark here at night, well, at least after the moon sets. I'm enjoying the CDK-20 a lot!

I'll definitely revisit this cluster - it was a lot more approachable than I'd imagined. (That's one reason I appreciate the sketches so much - it really helps set my expectations.)

#16 F.Meiresonne

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Posted 31 May 2009 - 04:52 AM

That's odd Jeff. To me, it seems that faint galaxies only get MORE visible as you increase


That does not work for me either. Last Friday i observed Hickson 68 and tried some of the members. Best views were with a N9T6 giving about 230x.
If i barlow my N13T6 most of the time that seems to much , loosing contast. I don't know why that is but it just seems too much.
This said i really did not study that effect at our dark site where galaxies are noticably brighter.It may be that and the fact that the scopes cooles down to slow. This weekend i am installing a bigger fan.I am also planning to get me a 7 mm widefield eyepiece, i don'tlike to barlow the T6 and even that may have something to do with it...
OTOH :
I don't see that effect on globs. M13 or a smaller glob in a barlowed N13T6 even N9T6 with a properly cooled mirror and descent seeing is astounding...or at least a far better sight
One another thing that comes to my mind. Jef and I live in about thesame climat and that is wet wet wet. Wet moisture is allways in the air and dims the views. In ohter words transparency is allways a concern. In the Provence is it about as dark then at our dark site over the Dutch border yet the views are alot better in France. But there in the summer the sky is sooo dry resulting in very clear skies.Galaxie light is probably the first that gets dimmed, stars like in globs can get easier through...IMO

#17 Jeff Young

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Posted 31 May 2009 - 08:54 AM

Very interesting. I'm glad John called me on my comments, becuase they don't turn out to jive with my prior observations either. Here's what I found in older notes:

  • I used 450X and 630X on two different nights on Stephan's Quintet to resolve NGC7317. So clearly higher power works for me on galaxies sometimes. Both nights were much better transparency than I had for the Coma cluster, but similar seeing. (But I did misidentify 7320C as a star in my Stephan's Quintet sketch.)
  • On the Deer Lick Group, I used 450X to get three of the fleas, but couldn't get the fourth at any power. Again, all 3 observations of this one were under better transparency, but indifferent seeing.
  • Similar to Freddy, I used 260X on HCG68, but my notes don't mention why. Excellent transparency (best ever recorded at my site), indifferent seeing.
  • I used 450X on HH1 and HH2. Excellent transparency that night, so-so seeing, and they were quite difficult.
  • Ahh... here's a good one: on a night of decent transparency, Mrk205 was difficult at 375X but moderately easy at 630X. I also used 630X on Mrk421, which was visible at lower mags but more swamped by the glare of the bright field stars.
OK, so I think it's clear that under normal conditions, I do find more mag helps with small, dim objects. What I remember with the Coma cluster, however, is that at 375X I got that gray-and-black blotchy field that my eye/brain tends to generate when the S/N goes to hell. Normally, that takes at least 450X with an OIII or 600X with a UHC -- I can't remember getting it with no filter.

The main thing that was different here was astronomical twilight. Perhaps that was killing the S/N more than my light pollution normally does? (It doesn't even get to astronomical twilight until several hours after I'd normally start observing -- perhaps tired eyes and/or brain were also a factor?)

Freddy --

Do you find that you often use more magnification during the darker nights of winter, or is the effect more-or-less constant for you?

-- Jeff.

#18 tatarjj

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Posted 31 May 2009 - 09:49 AM

Jeff, maybe that grey-black blotchy field was all the galaxies popping out of invisibility! Probably not, because you know your own vision, but just a thought.

As far as the seeing goes, personally, I find it has almost no effect on the highest usable power for galaxy/extended DSO observing. Bad seeing only spreads light out over like 5", which is alot smaller than almost all DSOs. Furthermore, since you are using adverted vision to view DSOs, and adverted vision has MUCH lower resolution than direct vision, then it only makes sense that the high usable power for SOLAR SYSTEM objects that require DIRECT VISION does not apply at all to DSOs.

All small and many of the brighter and larger galaxies look best for me in my 5mm regardless of seeing. Often, I use my 7mm Nagler due to its wider field making things easier to track. I would try out my 2.5mm to see what the effect of that is, but it gets tough to manually track at that power, and the objects rush by so quickly that your adverted vision hardly gets a chance to get a fix on them. Maybe someday if I can make my Servocat work (dang thing STILL doesn't work) I can try out my 2.5mm on galaxies. The only effect of seeing I really ever encounter on galaxy objects is sometimes, if seeing is very bad, faint stars will be spread out and fuzzed so much you have a hard time telling them apart from tiny, distant, high surface brightness galaxies.

I wouldn't THINK that astronomical twilight would have an effect on how power effects galaxy visibility- I can't see how. BUT, causes often have unexpected effects, and I never observe under astronomical twilight.

Oh, as far as a observing under a wet environment- those are my NORMAL observing sites. I often have puddles of dew that have dripped off my telescope at the end of a night of observing- or can make "snowballs" out of the frost I scrape off the scope. Sometimes my PRIMARY mirror frosts/dews over. I make extensive use of dew heaters, a 12V hair dryer, and even a fish tank air pump to keep my optics dew free. That picture of my 25" dob in the desert with mountains in the background for my avatar was from a vacation I took. So anyway, I don't think humidity is a factor.

Personally, I think the biggest factor is that not everyone's eye/brain works the same way. Maybe Jeff is right and astronomical twilight plays a role too.

#19 F.Meiresonne

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Posted 31 May 2009 - 04:14 PM

Do you find that you often use more magnification during the darker nights of winter, or is the effect more-or-less constant for you?



To me the effect is indeed constant. I never use high magnification on galaxies. I don't do this in my 8" scope either.
Last week we were at our dark site looking at M51. The best view was again in a 13 Ethos or 10 mm XW or N9T6 If i recall right. More was too much, loosing contrast and detail.
That was the overall consensus of 3 observers

#20 tatarjj

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Posted 31 May 2009 - 09:20 PM

Well, I can understand how you might find that increasing the power much more than like 200X on M51 might not provide you with a pleasing view. You tend not to need very high power on very big and bright galaxies to see alot of detail. Personally, I do not like my 5mm on M51- my most pleasing views come with my 7mm and 9mm Naglers. It's fainter galaxies I'm talking about needing very high power. Even the NGCs with my 25"- most of them are small enough to look best in my 5mm (540X). It has to do with the angular size of the galaxy- if they're much smaller than a certain threshold, pump the power up as much as possible, IMO.

#21 F.Meiresonne

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Posted 01 June 2009 - 05:29 AM

Ok, John, I try this out in the future. But i guess we are talking here about faint and small or did i get that wrong. That's true i mean i noticed it that small galaxies get visible if you cranck up the magnification.

#22 Jim Curry

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Posted 01 June 2009 - 07:19 AM

I think John's got it right that high power can bring out the fainter galaxies. I know you guys are talking about big glass but even with mine I've noticed that there are some galaxies that are undetectable at lower powers. While 95% of my observing takes place in the 100x - 133x range, when I'm pushing things during good transparency nights 166-200x will reveal objects at the very limits of detection. THat's why to me I don't worry about the formulas I see tossed around for brightness, exit pupil, on and on. It doesn't cost anything to put the next ep in to see what it will do. THat said, I don't bother chasing 14th mag stuff either.

Jim

#23 Jeff Young

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Posted 01 June 2009 - 03:58 PM

Yes, this is all starting to ring some bells.

Pumping up the power decreases the signal (by spreading it over a larger area), but that's not the whole story. The other half goes something along the lines of: if a few rods get a weak signal, the brain will throw it out, but if lots of rods get an even weaker signal, the brain will pay attention.

So for very small and dim targets, retinal coverage (image scale) can be more important than signal strength (image brightness).

But Jim really boils it down: it doesn't cost anything to try a combination already in your kit. The only thing I'd add (especially to self) is: record your results!

Cheers,
-- Jeff.

#24 tatarjj

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Posted 01 June 2009 - 09:09 PM

Yes, this is all starting to ring some bells.

Pumping up the power decreases the signal (by spreading it over a larger area), but that's not the whole story. The other half goes something along the lines of: if a few rods get a weak signal, the brain will throw it out, but if lots of rods get an even weaker signal, the brain will pay attention.

So for very small and dim targets, retinal coverage (image scale) can be more important than signal strength (image brightness).

Cheers,
-- Jeff.


Yes, this is exactly right. As magnification is increased, the brain is able to perceive details better and better up to a certain magnified detail size, DESPITE the fact that increasing magnification also decreases image brightness. I don't have the data with me, so I can't remember exactly what it is, but I believe it's about 2-10 degrees (apparent detail size) where the benefits of magnifying even more sorta plateau out. Past like 10 degrees, magnifying more only decreases the visibility of the specific detail. Keep in mind, this is for FAINT objects, using ADVERTED vision, and does NOT apply to planets. Also keep in mind that I say "details" not objects. This is why it's benefitual to use high power on big galaxies, to tease out small DETAILS. A "detail" could also be a very faint, round, featureless galaxy.

Oh by the way, keep in mind that CONTRAST is never changed when increasing/decreasing magnification, as contrast is strictly defined as object brightness/background brightness, both of which are affected equally by magnification changes. HOWEVER, the eye/brain PERCEIVES that the contrast is improved at higher magnification. Why this perception works this way, who knows, but it's part of the reason I personally prefer such high magnification all the time.

#25 Dave Mitsky

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Posted 01 June 2009 - 09:56 PM

Roger Clark was one of the pioneers in studying what he calls the Optimum Magnified Visual Angle.

http://www.clarkvisi...mva1/index.html

http://www.clarkvisi...-mag/index.html

Dave Mitsky






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