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Notes from Observing Session on March 23

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#1 Eddgie

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Posted 25 March 2020 - 10:38 AM

The first session I have had in a long time and I am guessing that due to the far lighter than normal vehicle traffic and the lessening of the smog that generally hangs over all metro areas, it was an exceptionally nice night. It followed a clear, bright, dry day with a nice blue sky. My SQM-L reading was much better than typical being a suburban 18.6, which is about as good as I ever get. 

 

Also, this was the first opportunity for me to really use my new Mod 3 and the first time in a long time that I had galaxies well positioned.

 

My primary DSO scope is my 12" dob, and this was used for all observations.  I know that most people seem to be chasing speed, but for galaxies, I find that while I can go far faster than f/4.9, the tradeoff in image scale is (to me personally) not worth it, as long as the intensifier being used is a good high performer.  I had been having some pointing issues with the dob the last few times I used it so before I left for my travels, I did a complete tune on it paying particular attention to the saddle plate (which was indeed loose, and needs a permanent solution, which I think will be drilling a hold and pinning it in place because the screws keep loosening). Last night, the scope Go2 was as good as new with all targets falling well into the field.  This important because it gives some confidence that on busy fields with bright galaxies, the target galaxy is well placed for identification, though last night it was trivially easy identifying galaxies just from the orientation vs Sky Safari Pro. Still, I like it when the scope Go2 is good, and last night it was pretty great. 

 

All observations were made with a Lumicon Deep Sky filter (a 650nm long pass) at prime focus.

 

It was the best galaxy night I have ever had from my back yard. Now I was still not able to see Mag 15 galaxies, but down to about Mad 13 galaxies, depending on the type of galaxy, viewing was great. I must have done 30 spots in the sky (slew) with a lot of star hopping from those spots so total galaxy count had to be maybe 100?  That is pretty awesome for a 2 hour session!

 

For example, the slew to  NGC 3605 put it almost dead center, and the tiny NGC 3607 was immediately and easily identified and shown almost exactly as represented by  the picture in Sky Safari Pro (I normally do not have the pictures on but did put them on for a particular observation and left them on, and will do so in the future because it helps me confirm details that I see at the eyepiece without having to search for pictures on the web, though I like to do that after the observations so I don't cheat by knowing the feature is there already). 

 

Lots of fields showed numerous galaxies.  I tend to use Go2 to get to a field and then just hop from there to explore other galaxies around that field.

 

One of the treats for me was detecting the dust lane in NGC 3628.  This was an almost invisible galaxy even on best nights when using my C14, but with the image intensifier and the benefit of a very good night, I was able to see this lane for the first time. It was not all that prominent because the galaxy itself does not have a particularly dense core to help it stand out, but it was nice to see this feature.

M65 and M66 were very interesting in that catalog puts M66 as the larger of the two, but due to the nearly face on orientation, the arms were so faint as to be extremely difficult to see (and usually not this good from my back yard, but a good night), but the neighboring M65 was awesome! While I could not really say I was able to pick out the small dust lane, this was probably the prettiest galaxy of the night.  The perspective of tilt seemed to be quite pronounced. Absolutely the best view ever from my back yard.

 

Markarian's Chain was an easy star hop and as with almost all of these other observations, the best ever from my back yard.  

 

A nice catch for me (first observation) was the Globular Cluster NGC 4147.  Visual magnitude is 10.31 and a total fail in the past using up to the C14.  It is a tiny little thing so even in the 12" at prime focus, at 4.4 arc minutes, it simply does not have enough extension to make it a grand object, and the core, while very bright, was just merged because there was no separation there, and the halo was just a very light sprinkling of stars.  I do not know the magnitude of these stars, but I am guessing in the Mag 14 and fainter range?  I just don't know, but since it was the first time I have ever seen it, I was delighted to have logged it.  

 

 

 

I was thrilled.  I attribute this in equal measures to the uncommonly good sky conditions (for my location) and the nice performance of the newest tube. Even at f/4.9, there was practically no noise of scintillation and this made the journey particularly pleasant.  There is not much here that was new for me, but almost everything here was more enjoyable than would be typical.

 

I am eager for us to see our way past the scourge of disease that has gripped our planet but mankind's severe impact on the environment is being lessened if at least temporarily, and during this time, I am hoping my sky conditions hold out just a few more days so I can get the Coma galaxies higher in the sky.   I rarely do a past 11:00 PM session, but if I have similar or better conditions tonight (we started a lock down at midnight last night) I will make an exception and stay up tonight for a rare-for-me post midnight session!

 

Stay safe.  I worry as much for the brave medical professionals and non-covid 19 patients as I do for myself.  They medical professionals are the true heros in this story.  I don't know if it is bravery or just an intense desire to help people, but whatever it is, they have my absolute admiration as being the greatest resource we have at this moment in time. If you are anyone you know is a medical professional dealing with this, make sure you express your gratitude and If you are one, you have mine.  Thank you for being on the front lines in spite of a system that is failing you. That is courage or devotion. I don't know which, but thank you for reaching deep for it. 


Edited by Eddgie, 25 March 2020 - 10:38 AM.

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#2 Tyson M

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Posted 25 March 2020 - 10:54 AM

I did a complete tune on it paying particular attention to the saddle plate (which was indeed loose, and needs a permanent solution, which I think will be drilling a hold and pinning it in place because the screws keep loosening).

Do you mean the finder bracket?  I am a bit confused on your saddle plate for your dob.  

 

Are you able to use lock nuts/lock washers?  Or loctite? 



#3 Eddgie

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Posted 25 March 2020 - 11:37 AM

It is the saddle plate that is mounted on the altitude drive shaft.   This accepts the rail that is on the side of the telescope.


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#4 Tyson M

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Posted 25 March 2020 - 11:54 AM

It is the saddle plate that is mounted on the altitude drive shaft.   This accepts the rail that is on the side of the telescope.

Sorry my mistake, I don't have the 12" GOTO dob.  



#5 Eddgie

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Posted 25 March 2020 - 12:38 PM

Sorry my mistake, I don't have the 12" GOTO dob.  

No worries. It was a good question and I can tell that your intention was to be helpful and there should never be an apology expected for trying to help someone. I appreciate that. 

 

Be safe. 


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#6 chemisted

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Posted 25 March 2020 - 01:37 PM

If you get the chance add a 2X barlow for your viewing of NGC 4147.  You will be treated to pinpoint stars throughout the cluster.  The same will be true for NGC 5634.



#7 Jeff Morgan

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Posted 25 March 2020 - 02:32 PM

A nice catch for me (first observation) was the Globular Cluster NGC 4147.  Visual magnitude is 10.31 and a total fail in the past using up to the C14.  It is a tiny little thing so even in the 12" at prime focus, at 4.4 arc minutes, it simply does not have enough extension to make it a grand object, and the core, while very bright, was just merged because there was no separation there, and the halo was just a very light sprinkling of stars.  I do not know the magnitude of these stars, but I am guessing in the Mag 14 and fainter range?  I just don't know, but since it was the first time I have ever seen it, I was delighted to have logged it. 

 

The Uranometria Deep Sky Field Guide list the brightest member stars as magnitude 14.5, with the horizontal branch at 16.9.

 

From SQM 18.5 skies and a 12.5" scope I would say that resolving some of those stars is an impressive catch!



#8 Eddgie

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Posted 25 March 2020 - 03:17 PM

If you get the chance add a 2X barlow for your viewing of NGC 4147.  You will be treated to pinpoint stars throughout the cluster.  The same will be true for NGC 5634.

Well, I should have gone in for my Barlow but I was not intending to do any Globulars.. It was close to where I was at the time so I hopped over to it just to see what I could see.  I was just to lazy to go in for a Barlow. Maybe tonight.



#9 Eddgie

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Posted 25 March 2020 - 03:26 PM

The Uranometria Deep Sky Field Guide list the brightest member stars as magnitude 14.5, with the horizontal branch at 16.9.

 

From SQM 18.5 skies and a 12.5" scope I would say that resolving some of those stars is an impressive catch!

Well, even under typical conditions I typically see 14.5 stars so I guessed they were 14 or less, but I did not know how much less.  I think on a similar night using the Micro with ULT tube I got down to 16.8 or 16.9 a couple of times. It is hard to know because I have to have really excellent position stars to validate and often it seems as if I can't get my charts to perfectly agree with the observed field. 

 

Also, we have to constantly remind ourselves that when using image intensifiers, redder stars can appear brighter than the catalogs suggest and the use of a long pass filter will slightly attenuate the blue stars so it really does make it somewhat hard to me to be confident when doing limiting magnitude reports. 

 

Anyway, thanks for the info.  I thought they were 14 or dimmer, but I just did not have anything with me to look it up. I have not used a conventional eyepiece in so long that I don't even know where the case is hiding.



#10 DanDK

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Posted 25 March 2020 - 04:28 PM

Eddgie, back in December I posted my plan for a new scope + NV, inviting suggestions, and you and several other helpful people steered me toward a dob rather than the SCT I was considering .  I got the 10" version of the Orion Go2 scope last month and have been very happy with it and its bright, sharp views.  Televue NV arrived last week.  My first peek at the night sky (through narrow cracks in the overcast) with the monocular alone was unforgettable. So was last night's strikingly bright view of M42 with the scope and Ha filter.

 

I like to galaxy hunt and I've had pretty good success, by my standards, with the new scope by itself.  You promised that night vision is quite good on galaxies, and since last week I'm a believer -- they're brighter and much easier to see.  M82 shows obvious structure I've never seen before, and I've had nice views of almost all of the brighter NGC galaxies I've looked for.

 

I have a question about magnification.  I ended up getting 3 Televue eyepieces: 55, 35, and 27 mm, which I believe gets me up to about 44X.  I'd like to go a bit higher for the smaller DSO's.  How high can I go and still get the NV benefit?

 

Again thanks to you and everyone else who helped me get started with NV.


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#11 The Ardent

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Posted 25 March 2020 - 04:45 PM

Not a Galaxy, but this was afocal with 6mm eyepiece giving 300x . Single iPhone handheld image cropped and inverted. 
I think it was the PVS7 Night Vision, not sure. From a few years ago. 
 

PN IC 4997 in Sagitta

 

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#12 Lukes1040

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Posted 25 March 2020 - 06:24 PM

Great session! I am hoping to stay up late enough to get my first glimpse of the coma galaxies with NV. This is going to be my first moonless clear night in months. Hoping for a memorable one.

#13 Gavster

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Posted 25 March 2020 - 07:29 PM

Eddgie, back in December I posted my plan for a new scope + NV, inviting suggestions, and you and several other helpful people steered me toward a dob rather than the SCT I was considering .  I got the 10" version of the Orion Go2 scope last month and have been very happy with it and its bright, sharp views.  Televue NV arrived last week.  My first peek at the night sky (through narrow cracks in the overcast) with the monocular alone was unforgettable. So was last night's strikingly bright view of M42 with the scope and Ha filter.

 

I like to galaxy hunt and I've had pretty good success, by my standards, with the new scope by itself.  You promised that night vision is quite good on galaxies, and since last week I'm a believer -- they're brighter and much easier to see.  M82 shows obvious structure I've never seen before, and I've had nice views of almost all of the brighter NGC galaxies I've looked for.

 

I have a question about magnification.  I ended up getting 3 Televue eyepieces: 55, 35, and 27 mm, which I believe gets me up to about 44X.  I'd like to go a bit higher for the smaller DSO's.  How high can I go and still get the NV benefit?

 

Again thanks to you and everyone else who helped me get started with NV.

I have just been comparing my 55mm plossl, 41mm panoptic, 27mm panoptic and 18.2mm delite with an f5 scope on m13, m82, needle galaxy and Leo triplet. Personally, I wouldn’t go any lower than the 27mm, the 18.2 just didn’t give as good views imo despite the extra image scale.


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#14 Jeff Morgan

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Posted 25 March 2020 - 08:41 PM

Well, even under typical conditions I typically see 14.5 stars so I guessed they were 14 or less, but I did not know how much less.  I think on a similar night using the Micro with ULT tube I got down to 16.8 or 16.9 a couple of times. It is hard to know because I have to have really excellent position stars to validate and often it seems as if I can't get my charts to perfectly agree with the observed field. 

 

Also, we have to constantly remind ourselves that when using image intensifiers, redder stars can appear brighter than the catalogs suggest and the use of a long pass filter will slightly attenuate the blue stars so it really does make it somewhat hard to me to be confident when doing limiting magnitude reports. 

 

Anyway, thanks for the info.  I thought they were 14 or dimmer, but I just did not have anything with me to look it up. I have not used a conventional eyepiece in so long that I don't even know where the case is hiding.

 

There are certainly some thorny issues in estimating just how deep one is going with a NVD. The device showing so many stars being one of them! Reliable charts and data being very close behind. Oh, and it tends to be tedious work instead of relaxation at the eyepiece.

 

I am not certain how big the color issue is. Of course stars like Betelgeuse and Aldebaran (to name two) are "over sampled" by the nature of the detector. But all stars - even the blue ones - emit across the entire visual spectrum (and beyond).

 

I am liking the Globular Cluster method though. When resolving stars within a cluster, I can be absolutely confident I'm getting the brightest members (at a minimum). Professionally derived quantitative magnitude data is available to establish the magnitude reached.

 

Globulars are also plentiful and provide a relatively small search area (very convenient). OTOH, finding deep magnitude data for individual stars and matching up larger star fields is difficult in practice. SkySafari Pro only goes down to magnitude 15.

 

True there could be random line-of-sight issues with foreground stars, but there are large numbers of globulars (many in star-poor areas of sky) to factor that out.

 

And if one argues that we really not seeing cluster members but instead seeing foreground stars (which are not visible conventionally by the way!), that assertion by itself also indicates we are reaching impressive depths for a given aperture.

 

In the end whether it is Red, Blue, two magnitudes, three, or four the performance gain is impressive and I am a happy camper!



#15 The Ardent

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Posted 25 March 2020 - 08:55 PM

NV is especially good for globulars because 1. Faint stars are amplified at the best efficiency because they are the highest surface brightness DSO’s  2. Red stars are amplified the better because the black body curve syncs with NV sensitivity  3. Globulars contain mostly old, red stars. 

Chemisted can correct my hypotheses. 



#16 a__l

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Posted 25 March 2020 - 09:18 PM

All observations were made with a Lumicon Deep Sky filter (a 650nm long pass) at prime focus.

 

 

What benefits will have Lumicon Deep Sky Filter - 2" # LF3015 before Lumicon Night Sky Hydrogen-Alpha Filter - 2" # LF3090?

You will see better contrast with this SQM? The issue is relevant for galaxies and stars. The difference in the price of filters is ~ 2.5 times. Has the meaning?

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Edited by a__l, 25 March 2020 - 09:22 PM.


#17 Jeff Morgan

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Posted 26 March 2020 - 12:28 AM

What benefits will have Lumicon Deep Sky Filter - 2" # LF3015 before Lumicon Night Sky Hydrogen-Alpha Filter - 2" # LF3090?

You will see better contrast with this SQM? The issue is relevant for galaxies and stars. The difference in the price of filters is ~ 2.5 times. Has the meaning?

 

It would be nice to have a "Silver Bullet" filter for galaxies as we do for emission nebula. But galaxies emit across the spectrum.

 

While the Deep Sky cuts out prominent light pollution lines, street lights are not monochromatic (except perhaps the newer LED's?). They may peak at a particular line (mercury, sodium, whatever) but still produce signal across the spectrum. As a test, take any nebular filter you have handy and hold it up in front of a streetlight.

 

And of course there are many other artificial light sources present in a city.

 

A year or two ago I tried a similar strategy with the DGM GCE (Galaxy Contrast Enhancer) filter under my 20.5 skies. I could not see a noticeable improvement.

 

It's worth a shot I suppose, under your local conditions you may like the result.


Edited by Jeff Morgan, 26 March 2020 - 12:30 AM.


#18 a__l

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Posted 26 March 2020 - 02:49 AM

I'm a little about something else. If you look at the red band of these two filters, it is the same. Adds extra contrast availability blue-green band at the Deep Sky filter? Or worsens (due to light pollution)?



#19 chemisted

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Posted 26 March 2020 - 08:33 AM

NV is especially good for globulars because 1. Faint stars are amplified at the best efficiency because they are the highest surface brightness DSO’s  2. Red stars are amplified the better because the black body curve syncs with NV sensitivity  3. Globulars contain mostly old, red stars. 

Chemisted can correct my hypotheses. 

Your points are good ones, Ray.  I would add a fourth: very many summertime globulars also have interstellar dust blocking their light and this makes the visual magnitude of their stars dimmer by 1-5 magnitudes.  The generation 3 intensifiers have peak sensitivity in the near infra-red and these frequencies are less affected by dust so more of those photons make it to the telescope than visual photons.  So the combination of two effects (a preponderance of red emitting stars and increased numbers of photons relative to visual wavelengths) make globulars the ideal targets for NV devices.  With my current equipment I can see 18th visual magnitude stars in the most dust blocked clusters even though I only have 10" of aperture.


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#20 Jeff Morgan

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Posted 26 March 2020 - 12:58 PM

Your points are good ones, Ray.  I would add a fourth: very many summertime globulars also have interstellar dust blocking their light and this makes the visual magnitude of their stars dimmer by 1-5 magnitudes.  The generation 3 intensifiers have peak sensitivity in the near infra-red and these frequencies are less affected by dust so more of those photons make it to the telescope than visual photons.  So the combination of two effects (a preponderance of red emitting stars and increased numbers of photons relative to visual wavelengths) make globulars the ideal targets for NV devices.  With my current equipment I can see 18th visual magnitude stars in the most dust blocked clusters even though I only have 10" of aperture.

 

Good point. I was only thinking of the stars themselves, not the intervening dust and the reddening effect of it.

 

Just like a volcanic sunset, red get through with less attenuation, shifting the perceived color balance.



#21 a__l

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Posted 26 March 2020 - 04:12 PM

Your points are good ones, Ray.  I would add a fourth: very many summertime globulars also have interstellar dust blocking their light and this makes the visual magnitude of their stars dimmer by 1-5 magnitudes.  The generation 3 intensifiers have peak sensitivity in the near infra-red and these frequencies are less affected by dust so more of those photons make it to the telescope than visual photons.  So the combination of two effects (a preponderance of red emitting stars and increased numbers of photons relative to visual wavelengths) make globulars the ideal targets for NV devices.  With my current equipment I can see 18th visual magnitude stars in the most dust blocked clusters even though I only have 10" of aperture.

This is not true. Dust absorption decreases approximately in proportion to 1/lambda (wavelength). The sensitivity of the Gen3 sensor decreases sharply after 800 nm (see my post graph above).

 

Besides, in this case, you are observing the photospheres of stars, not own dust light.

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#22 chemisted

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Posted 26 March 2020 - 05:55 PM

This is not true. Dust absorption decreases approximately in proportion to 1/lambda (wavelength). The sensitivity of the Gen3 sensor decreases sharply after 800 nm (see my post graph above).

 

Besides, in this case, you are observing the photospheres of stars, not own dust light.

Tell it to the editors of Sky & Telescope.  They published my article:  Seeing Through the Dust by Ed Mihelich, S&T2017, July issue, pages 57-59.



#23 a__l

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Posted 26 March 2020 - 10:54 PM

Is it scientific research, confirmed for the range 800-900 nm Gen3 for 1-5 magnitudes (dust)?
Is there a rebuttal to empirical formula 1/lambda absorption for dust? You should probably refer to a peer-reviewed scientific magazine.


Edited by a__l, 26 March 2020 - 10:58 PM.


#24 star drop

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Posted 26 March 2020 - 10:56 PM

Let us get back on topic please.




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