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Martian Moons

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#51 CrazyPanda

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Posted 19 October 2020 - 08:21 AM

You have seeing so bad that it affects your naked eye observing? That would be of the order of 60-200" to affect the naked eye view. Thats a poor observing site!

 

I dont think ive ever seen worse than 15" and that was noteworthy.

New England has truly abysmal seeing, and yes, it's bad enough to affect naked eye observing. Only on nights when I can roughly see Airy patterns in my telescope do I see the faintest stars naked eye. The more concentrated the light from those stars remains, the more easily I can see them. On steady nights, that equates to about 0.3 to 0.4 magnitudes for me.


Edited by CrazyPanda, 19 October 2020 - 08:23 AM.


#52 happylimpet

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Posted 19 October 2020 - 09:45 AM

New England has truly abysmal seeing, and yes, it's bad enough to affect naked eye observing. Only on nights when I can roughly see Airy patterns in my telescope do I see the faintest stars naked eye. The more concentrated the light from those stars remains, the more easily I can see them. On steady nights, that equates to about 0.3 to 0.4 magnitudes for me.

But surely there is an enormous gulf between nights with 100-200" seeing when the stars are visibly blurred naked eye, and nights when the airy pattern is roughly visible, at maybe 2-3" or so?

 

We are getting off topic though.



#53 CrazyPanda

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Posted 19 October 2020 - 10:44 AM

But surely there is an enormous gulf between nights with 100-200" seeing when the stars are visibly blurred naked eye, and nights when the airy pattern is roughly visible, at maybe 2-3" or so?

 

We are getting off topic though.

I guess I question whether seeing actually has to be 100-200" bad for it affect naked eye visibility right at the threshold of observability. I don't think it does.

 

If you can see stars twinkling, you have bad enough seeing conditions that naked eye visibility is affected. Doesn't have to be 100-200" for twinkling to be visible.



#54 Redbetter

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Posted 20 October 2020 - 04:00 AM

I guess my point is that glow around Mars doesn't seem to be a factor for me (I'm talking about the actual glow from scatter and diffraction and atmosphere etc). There's very little of it much past about 10 arc seconds from the planet that I can see. It's not "etched", but it's quite well controlled.

 

But that's different from the actual *glare* of the planet and how that extra light impacts your vision. That glare is present whenever Mars is in the field, thus to me, it renders Deimos' separation an irrelevant factor. It could be 120" away from Mars and I still don't think that would help me see it short of moving Mars out of the field while keeping Deimos in it and letting my eyes dark adapt further.

 

Regarding seeing, I'm just replying to your early statement that if seeing is good enough for Phobos, then Deimos should be super easy (paraphrased). That has never been my experience with any faint star observing. The fainter the star, the better the seeing has to be to see it. 

 

So it could very well be that my seeing was good enough for Phobos, but not good enough for Deimos.

Some of the assertions above are not accurate from what I see.

  • Starting with the idea that there is little glow post about 10 arc seconds.  Untrue, from what I have seen.  I can see this visually just looking at the field and noticing the background grows darker away from the planet the further one goes.  This is true even if I employ an occulting bar, or an eyepiece that allows a sharp cutoff at the field edge with Mars out of the field (e.g. 3-6 TV Zoom on the 3, 4, or 5 settings.)  Phobos is still in the steeper part of this gradient, and never really leaves it, even at 20 or 30 arc seconds from the planet's surface.    
  • An occulting device, or removing Mars from the field to just outside the edge, eliminates much of the direct glare hitting the eye.  This is a useful way to improve visual contrast, but it is also reveals that the field is not a uniform dark background or uniformly illuminated as you propose.  This can be seen in images as well.  
  • When the seeing is poor, that gradient is worse.  I have noticed that many, many times.   
  • Neither Phobos nor Deimos are truly dim near opposition for medium or large aperture, as they are likely at the direct vision level...rather than averted, if not for the glare.  The reason they aren't readily visible is because of the glare from Mars, both direct and that gradient.  Deimos being further out suffers less from the glare/gradient, that is why most of us see it more easily despite being a magnitude dimmer.   Deimos generally being easier to detect is a well-known phenomenon, although there do appear to be some people such as yourself that see this differently (and I have an idea as to why that might be, which I will follow up on in a subsequent post.)
  • Poor seeing not only hurts the base contrast around the planet, it also limits the effective magnification that could otherwise be used to boost contrast for these stellar appearing objects.  But again it is not the seeing that is limiting visibility of Deimos with respect to its magnitude, it is the loss of contrast from the planet's glow combined with the seeing blurring of the points, and that contrast impact is worse for Phobos than Deimos near elongation.
  • I don't think dark adaptation is as much of a factor as we typically assume for this...another thing I will follow up on.

I don't know if you have any eyepieces of a type that could be employed with some sort of occulting bar/disk/semi-circle.  You need an eyepiece with an external field stop--I use and old TV Plossl.  If you do, and they can be used in a desired magnification range, that could help your observations.  

 

As far as observations go, the majority of folks that find either of the moons locate Deimos (Allan has done it with a 130mm Tak.)    Some of us have seen each of these moons dozens of times over multiple oppositions, sometimes in more than one aperture.  While you aren't seeing Deimos, a number of us are, and consider it the easier to locate most of the time.  You and I are trying to understand what is different about our experiences.  I am learning some things about this as I try new ways of observing the moons (and I have learned that several magnitude of smoke dimming sometimes has some unexpected positive consequences for this sort of thing.)



#55 Redbetter

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Posted 20 October 2020 - 05:32 AM

CrazyPanda,

 

Now for the follow up portion.   Based on your comments and some observing I did Sunday night, I think some of the difference might be in the way we actually observe/or in the way our eyes' specific sensitivities to direct/indirect (averted vision) detection and background glare.  For me it is natural to detect faint objects in averted vision, even when well-separated from where I am focused.  For me even "direct" vision tends to be rather indirect when observing--including for finding the most detail in planetary features.    

 

I did some observing on Sunday night at my dark site (~21.45 MPSAS at the time), and interrupted DSO observing for over an hour to do some tests with the 20" with and without an 8" off-axis mask with and without the occulting bar. The seeing was not as steady as hoped, with some cool but very light breeze keeping things disrupted enough that planetary viewing was unsatisfactory, even with the 8" mask.  So while I could use 278x to some effect, and even 338x with the occulting bar this was all pushing it.  Pickering wise it was about 3/10 in the 20" at best, with continuous fluctuation of focus.

 

I knew that Phobos and Deimos were nearing elongation during the time I set aside for Mars observing, on opposite sides of the planet.  Upon focusing on the planet with full 20" aperture at 278x I immediately noticed Deimos in peripheral vision, while staring at the planet.   Phobos was not so readily seen.  I had to hunt for it for a time, waiting for some better seeing/focus to finally give it away in the glare.  After that I could find it more readily, although not like Deimos.  Neither of the moons were in the spider vane diffraction rays initially.  

 

I then put the 8" mask on (so clear aperture with no vanes.)  This smaller aperture helped somewhat in steadying Mars, but focus was still drifting with the very light breeze, and the seeing was not good enough for sketching, even with #25 filter.  The breeze was most noticeable for about 20 minutes when I was using the 7.4mm with occulting bar (338x) trying to detect the moons with 8".  While I could get Deimos at times, I had real trouble with Phobos, even though I knew where it was.  I could not get it by drifting and tracking with the bar perpendicular to the motion (needed too much precision.)  I finally was able to turn the occulting bar in a way that the planet ran partially down its length, allowing Phobos to be caught moving along its edge when the seeing would sharpen. 

 

As the seeing recovered somewhat I dropped down to 278x to see I could detect the moons in 8" without the occulting bar's help.  This proved interesting, because I was again picking up Deimos very weakly in averted vision at moments.  However, this time when I would direct my gaze toward the glint of Deimos I would nearly always lose it, and have to turn back to the planet to pick it up again.  I then found Phobos very weakly, but could hold it in moments of better seeing.  Looking directly at the planet I could see both moons simultaneously in indirect vision. 

 

Finally, after doing some filtered observing of the planet with and without the mask, I turned back to the moons unfiltered at 278x with the full 20".  Now both moons had rotated relative to the vanes and were essentially in the very center of the spider vane diffraction rays.  What I noticed was that I could pick up Deimos immediately in averted vision, then look at it essentially directly or with scant offset.  Phobos was a little different in that it showed up more weakly in averted vision.  However, if I stared directly at the spot I knew it to be in, I could lock on after a time and hold it, somewhat better than I had in indirect vision.  Again I could see both moons simultaneously in averted vision when looking at the planet when the seeing was more settled, even though they were in the diffraction rays.

 

As I have seen many times before, the more marginal/poor the seeing, the harder it is for me to see Phobos.  Deimos doesn't fade out as easily, and when well separated from the planet it pops into view by comparison.  However, the interesting difference in this is that I was doing some direct vision searching for Phobos and seeing it better than I normally do in averted vision...but only if I was looking right at the spot (in this case a well known spot during the session.)  Averted vision was still stronger for locating Phobos in the first place.  Deimos was not helped by truly direct vision, and was in some ways hurt or lost by attempting the direct vision approach.

 

I think this might indicate differences in the way we habitually search the visual field for such objects and lock on to them.  Whether or not it reflects any physiological sensitivity differences or just habit/technique I  don't know.  (Although your either not seeing the gradient or not considering it noticeable enough to be a factor, and so far not seeing Deimos, has me suspecting some sensitivity differences across extended fields.  Direct or near direct sensitivity/acuity might be the same or even better for you.)  I know that if the seeing cooperates, I can locate both moons with averted vision search techniques.  One moon, always relatively near the bright planet responds to direct for me (if I employ it), the other does not.


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#56 CrazyPanda

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Posted 20 October 2020 - 11:14 AM

Starting with the idea that there is little glow post about 10 arc seconds.  Untrue, from what I have seen.  I can see this visually just looking at the field and noticing the background grows darker away from the planet the further one goes.  This is true even if I employ an occulting bar, or an eyepiece that allows a sharp cutoff at the field edge with Mars out of the field (e.g. 3-6 TV Zoom on the 3, 4, or 5 settings.)  Phobos is still in the steeper part of this gradient, and never really leaves it, even at 20 or 30 arc seconds from the planet's surface.

 

Maybe we have different optics or different levels of transparency, but aside from some obnoxious reflections and flaring from my Meade #140 barlow, when Mars is outside the field of view, it's very difficult to detect *where* outside the field of view it is, using the gradient around it. The gradient is certainly not strong enough to obscure Phobos even at 12 seconds in.

 

But what's also interesting is Phobos and Deimos will be optical point sources, meaning their brightness increases by the square of the aperture. The surface brightness of all other light in the field is based on the exit pupil. Maybe there's some optimum between magnification, aperture, and exit pupil as it relates to how easy or hard it is to separate Phobos from whatever glow might be present around Mars.

 

 

 

Averted vision was still stronger for locating Phobos in the first place.

 

This is my experience as well. Each time I noticed Phobos it was because I was either looking at Mars or still positioning Mars in the view (I actually find that sometimes deliberately inducing motion makes things much easier to see, since that's how human vision is wired), but then I could lock in on it in direct vision.

 

 

 

I knew that Phobos and Deimos were nearing elongation during the time I set aside for Mars observing, on opposite sides of the planet.  Upon focusing on the planet with full 20" aperture at 278x I immediately noticed Deimos in peripheral vision, while staring at the planet.   Phobos was not so readily seen.  I had to hunt for it for a time, waiting for some better seeing/focus to finally give it away in the glare.  After that I could find it more readily, although not like Deimos.  Neither of the moons were in the spider vane diffraction rays initially.

 

278x in 508mm aperture is a 1.82mm exit pupil. In contrast, the last time I was easily able to spot Phobos (at about maybe 17-18" separation), it was 246x and 1.54mm exit pupil.

In terms of surface brightness, that's a difference of (1.82/1.54)^2 = 1.4x brighter surface brightness.

 

In terms of magnitude increase, that's (20/15)^2 = 1.76x point source brightness increase.

 

So it's interesting that in your 20" at 278x, Phobos would have had proportionally *better* contrast against the surface brightness of any glow, than in my 15" at 246x, and yet you didn't find it as easy to notice.

 

So either:

 

1. For whatever reason, there is more glow around Mars at the time of your observation (differences in scope contrast, optical quality/cleanliness, transparency, cornea/retinal differences)

2. The extra size of Mars combined with the slightly higher apparent surface brightness in your scope introduced more glare for your eye that overcame the proportionally brighter point source of the Moon. But based on *my* experience, that extra glare would render Deimos just as hard to see (and again, I'm differentiating glare - which is the flooding of the retina with light from Mars - from *scatter* which is a visible glow around Mars that's present even when Mars is not in the field).

 

I'm still not convinced that seeing conditions can make "scatter" (e.g. glow around Mars) so substantially worse that it would make Phobos (at elongation) harder to see. That doesn't track logically for me and I've never observed that phenomenon to such a degree on any planet. Transparency I get, but seeing conditions would have to be so bad that the sky is basically behaving like frosted glass. And if seeing conditions are truly that bad, then the fainter light of Deimos should have been erased into a blur.

 

Concerning my seeing conditions, this is a typical night for me: https://www.youtube....h?v=hSGGZMzOAU8

 

This is one of the best nights I've ever had - better than most of my Mars sessions: https://www.youtube....h?v=kHc3Nkys1XI (which is still poor compared to say, this: https://www.youtube....?v=RavpiN0Axj4)

 

I have VERY, VERY, VERY bad seeing conditions most of the time. A few nights I get decent result, but they are still poor compared to most other locations.

 

On the very best nights, I can see about 2-3x the number of stars in M13 than I can on typical nights. The fainter the point source of light, the more susceptible it is to bad seeing.


Edited by CrazyPanda, 20 October 2020 - 11:17 AM.


#57 happylimpet

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Posted 20 October 2020 - 11:57 AM

 

But what's also interesting is Phobos and Deimos will be optical point sources, meaning their brightness increases by the square of the aperture. The surface brightness of all other light in the field is based on the exit pupil. 

Based on the square of the exit pupil, and also the square of the aperture.


Edited by happylimpet, 20 October 2020 - 11:58 AM.


#58 CrazyPanda

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Posted 20 October 2020 - 12:58 PM

Based on the square of the exit pupil, and also the square of the aperture.

This is not correct. The apparent surface brightness of objects is governed *solely* by exit pupil.

 

Meanwhile the brightness of optical point sources (those whose angular size is below the resolving power of the telescope) is governed solely by aperture and not exit pupil (until your magnification is so great you're actually just magnifying the Airy pattern and spreading its light out against a greater area on your retina - then the surface brightness of the Airy pattern will decrease). But that requires magnifications well beyond any normal practical limit.


Edited by CrazyPanda, 20 October 2020 - 01:00 PM.


#59 happylimpet

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Posted 20 October 2020 - 02:28 PM

This is not correct. The apparent surface brightness of objects is governed *solely* by exit pupil.

 

Meanwhile the brightness of optical point sources (those whose angular size is below the resolving power of the telescope) is governed solely by aperture and not exit pupil (until your magnification is so great you're actually just magnifying the Airy pattern and spreading its light out against a greater area on your retina - then the surface brightness of the Airy pattern will decrease). But that requires magnifications well beyond any normal practical limit.

I suppose I wasnt very clear. Those arent independent variables.

 

For the same scope, double the exit pupil, and the surface brightness of the sky or any other extended source goes up by a factor of 2^2 or 4; point source is unchanged.

 

Double the aperture, maintain everything else, and the surface brightness and/or point source brightness go up by a factor of 4.



#60 Redbetter

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Posted 20 October 2020 - 05:58 PM

Maybe we have different optics or different levels of transparency, but aside from some obnoxious reflections and flaring from my Meade #140 barlow, when Mars is outside the field of view, it's very difficult to detect *where* outside the field of view it is, using the gradient around it. The gradient is certainly not strong enough to obscure Phobos even at 12 seconds in.

 

But what's also interesting is Phobos and Deimos will be optical point sources, meaning their brightness increases by the square of the aperture. The surface brightness of all other light in the field is based on the exit pupil. Maybe there's some optimum between magnification, aperture, and exit pupil as it relates to how easy or hard it is to separate Phobos from whatever glow might be present around Mars.

 

 

278x in 508mm aperture is a 1.82mm exit pupil. In contrast, the last time I was easily able to spot Phobos (at about maybe 17-18" separation), it was 246x and 1.54mm exit pupil.

In terms of surface brightness, that's a difference of (1.82/1.54)^2 = 1.4x brighter surface brightness.

 

In terms of magnitude increase, that's (20/15)^2 = 1.76x point source brightness increase.

 

So it's interesting that in your 20" at 278x, Phobos would have had proportionally *better* contrast against the surface brightness of any glow, than in my 15" at 246x, and yet you didn't find it as easy to notice.

 

So either:

 

1. For whatever reason, there is more glow around Mars at the time of your observation (differences in scope contrast, optical quality/cleanliness, transparency, cornea/retinal differences)

2. The extra size of Mars combined with the slightly higher apparent surface brightness in your scope introduced more glare for your eye that overcame the proportionally brighter point source of the Moon. But based on *my* experience, that extra glare would render Deimos just as hard to see (and again, I'm differentiating glare - which is the flooding of the retina with light from Mars - from *scatter* which is a visible glow around Mars that's present even when Mars is not in the field).

 

I'm still not convinced that seeing conditions can make "scatter" (e.g. glow around Mars) so substantially worse that it would make Phobos (at elongation) harder to see. That doesn't track logically for me and I've never observed that phenomenon to such a degree on any planet. Transparency I get, but seeing conditions would have to be so bad that the sky is basically behaving like frosted glass. And if seeing conditions are truly that bad, then the fainter light of Deimos should have been erased into a blur.

 

Concerning my seeing conditions, this is a typical night for me: https://www.youtube....h?v=hSGGZMzOAU8

 

This is one of the best nights I've ever had - better than most of my Mars sessions: https://www.youtube....h?v=kHc3Nkys1XI (which is still poor compared to say, this: https://www.youtube....?v=RavpiN0Axj4)

 

I have VERY, VERY, VERY bad seeing conditions most of the time. A few nights I get decent result, but they are still poor compared to most other locations.

 

On the very best nights, I can see about 2-3x the number of stars in M13 than I can on typical nights. The fainter the point source of light, the more susceptible it is to bad seeing.

You seem to be only understanding pieces of what is being said, or cherry picking and ignoring the whole. I will summarize some key points that merit your consideration/reconsideration:

  • Unless I have missed it somewhere, you still haven't seen Deimos.  I and others have done it frequently around opposition (some of us over various oppositions).  It might just be that we have some idea what we are talking about.
  • Allan has found Deimos with a 130mm refractor.  I have seen it multiple times now using 8" of aperture via off-axis mask.  Others find it with 10" and 12" scopes, etc.   
  • Those of us who have seen it have found it more readily than Phobos. (This was true even at the time of its discovery.)
  • Reported Phobos observations are generally rarer, despite it being 1+ magnitude brighter and (if seen) it would be more readily recognized as belonging to Mars than Deimos which is further away and dimmer.
  • Perhaps if you employed an occulting bar the glow around Mars would be more apparent to you.  

Perhaps I am wasting my time trying to break someone out of circular logic, but I'll make a (hopefully) final pass at it:

 

1.  You said, "The gradient is certainly not strong enough to obscure Phobos even at 12 seconds in."  This is false.  Whether you can see the gradient or not, it is there (and images show it, even outside of the overexposed zone closest to the planet.)  If it was not enough to obscure Phobos, then we could see Phobos frequently, through a wide span on either side of the opposition date.  All one would need was an occulting bar and enough aperture to show objects down to roughly 12th magnitude, and there Phobos would be whenever it was 12 arc seconds away from the planet.  Instead, it goes missing in large aperture even at elongation on close approaches of Mars whenever the seeing is insufficient.  [The occulting bar would only be necessary to remove glare to the eye, not the optics.]  Yet even with an occulting bar Phobos is missing much of the time, and more so in poor seeing.  This cut off isn't in 12 arc second level seeing ...it is down in the 2 arc second range or somewhat better.  2 arc second is typical at my dark sky sites and I typically see down into the low 17's in such conditions with the 20".  

 

2.  You went into an optical point sources and surface brightness discussion but missed some of the most basic considerations.  You overlooked that I also used 8" of aperture for the sightings, 0.73mm exit pupil result.  That is 4.45x lower surface brightness than your 15" provides in your example.  And yet I could see Deimos this way, even without an occulting bar.  So there is a huge problem in your theory about the differences, trying to lay it on optical quality, etc.  

 

3.  You dismiss seeing, but it is the biggest factor I have found.  You described one of your 3 Phobos sightings as Pickering 6 in a 15".  That is very good seeing, sub-arc second.  Phobos is easy in those conditions.  It is more challenging in seeing that is about 3x wider in arc second rating (e.g. Pickering 3 in the 20".)    The glow around things gets broader in poor seeing, tighter in good seeing.  In addition, Phobos and Deimos are no longer truly point sources as the seeing declines and magnification increases.  Their contrast relative to the background gradient declines because they are spread out as well.  Certainly that is the case in the 250 or 300x range with seeing that is closer to 1.5 arc seconds.  

 

4.  About transparency...surprisingly, I have found that to be the smallest factor with this sort of observation.   That point was driven home when I was observing both moons in my red zone backyard (bright skies) through several magnitudes of smoke dimming.  Phobos proved easy for the 20" when seeing was the most stable and the smoke was thick.  Over a few minutes time as the smoke was thinning and some stars could actually be seen overhead, the seeing began to suffer and Phobos became hard to spot.  It isn't transparency or dark skies that matter most for this, it is stable seeing. 

 

5.  At max elongation, Deimos is roughly 3x further from the planet's surface than Phobos.  You dismiss this as inconsequential with respect to the background gradient, yet visually it is apparent to me.  Calcs I already provided suggest that the background glow provided by Mars could be around 9x weaker at this separation than at Phobos' separation.  By comparison Phobos is less than 3x brighter than Deimos, so the contrast impact is 3x more in Deimos favor.  It is no wonder that Deimos is more readily observed and reported.  This would also explain why I found very poor transparency (in the form of smoke in bright sky) had little impact and was instead overwhelmed by very good seeing.  

 

6.  You say that you don't see the seeing effect with respect to glow/scatter around other planets.  I see it all the time with a range of apertures, including targeting Enceladus with the 110 refractor or 127 Mak.  In the 20" Mimas is one of the best seeing indicators.  It pops right into view when the seeing is good.  If the seeing is mediocre it doesn't matter how dark or transparent the sky is, Mimas goes missing.  This is also apparent with Neptune/Triton, and with Uranus and its four brightest moons.  The two inner ones are very hard to pick up when the seeing is mediocre/poor or very poor.  


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#61 CrazyPanda

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Posted 20 October 2020 - 06:42 PM

You said, "The gradient is certainly not strong enough to obscure Phobos even at 12 seconds in."  This is false.

 

So how was I able to spot it fairly easily (unprompted, without looking for it) even in mediocre seeing? And yes, Pickering 6 is mediocre seeing at best.

 

You dismiss seeing, but it is the biggest factor I have found

 

I don’t dismiss seeing, but I categorically reject the notion that Phobos needs better seeing than Deimos and I caterogically reject the notion that bad seeing causing more light scatter from Mars is why Phobos is harder to spot, and not the bad seeing obscuring Phobos *itself*.


Edited by CrazyPanda, 20 October 2020 - 06:48 PM.


#62 Redbetter

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Posted 20 October 2020 - 08:59 PM

So how was I able to spot it fairly easily (unprompted, without looking for it) even in mediocre seeing? And yes, Pickering 6 is mediocre seeing at best.

This is drifting way off topic.  There is nothing consistent about what you are saying, other than the inconsistency of it.  You went on about how awful your seeing was normally, yet earlier said it was Pickering 6 in your 15" for the observation and called it mediocre.   None of that adds up.  Having a decent diffraction pattern in a 15" (Pickering 6) is very good seeing.  The Pickering rating system was actually developed using a 5" scope.  Even by that scale with a 5" -- 3x less sensitive than the same rating in a 15"-- it is listed as "fair to good"--not "mediocre at best".   The disconnect here is orders of magnitude.

 

I don’t dismiss seeing, but I categorically reject the notion that Phobos needs better seeing than Deimos and I caterogically reject the notion that bad seeing causing more light scatter from Mars is why Phobos is harder to spot, and not the bad seeing obscuring Phobos *itself*.

Bad seeing doesn't obscure Phobos itself near opposition.  It is 11th magnitude!!!  That is visible in bright skies with medium aperture in awful seeing absent a bright nearby planet, let alone a 15" scope in any seeing.  It however is not visible near an extremely bright planet in poor seeing.

 

So it isn't seeing alone that is the issue, it is the proximity to the planet and the glow surrounding the planet, which decreases with distance.  Seeing impacts both the moons and the background.   Again, an occulting bar will reveal how much of a factor this is, because it eliminates the direct glare of the planet, but leaves the halo not covered by the bar.  The surprising thing is that the bar only helps in a limited way when the seeing is poor.

 

Anyway, you haven't found Deimos; and you are convinced that separation plays virtually no part in visibility of the moons...well other than at 12 arc seconds or so where a switch is flipped in your basis.  Meanwhile, people who have observed Deimos generally have the opposite impression of visibility.  It appears that no amount of reason I can provide is going to inform your opinion, so I don't know why I even bothered.


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#63 CrazyPanda

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Posted 20 October 2020 - 09:34 PM

It appears that no amount of reason I can provide is going to inform your opinion, so I don't know why I even bothered.

 

My opinion will be informed by own personal observations thank you very much.

 

Those observations show scatter around Mars being significantly better controlled than your description of it. Why? I can't say. It just is.

 

Those observations are Phobos 3 times unprompted (with separations of roughly ~12", ~20", and ~17"), Deimos 0 times actively looking. Bad timing for Deimos observations maybe, or for *my eyes*, the glare from Mars combined with seeing conditions is too much for them to detect 12th mag Deimos.

 

Those observations tell me that just because seeing is good enough to see Phobos, it is not a guarantee that it's good enough to see Deimos (which is the opposite of your claim).

 

If I ever do finally have the opportunity to observe both at optimum separation, I will make my own determination as to which is the easier of the two (I'm going to bet it's still Phobos wink.gif )


Edited by CrazyPanda, 20 October 2020 - 09:35 PM.


#64 happylimpet

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Posted 21 October 2020 - 06:00 AM

My opinion will be informed by own personal observations thank you very much.

 

 

Or in your case of Deimos, lack of.

 

Odd how youre such an expert on something you havent done and yet those who have done it are all wrong.

 

I know Im as guilty as anyone, but its a shame whats happened to this thread.

 

Shall we go back to discussing our observations?


Edited by happylimpet, 21 October 2020 - 06:01 AM.

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#65 CrazyPanda

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Posted 21 October 2020 - 08:01 AM

Or in your case of Deimos, lack of.

 

Odd how youre such an expert on something you havent done and yet those who have done it are all wrong.

 

I know Im as guilty as anyone, but its a shame whats happened to this thread.

 

Shall we go back to discussing our observations?

A lack of an observation of something you were trying to observe is a a valid observation in itself.

Why is it that *you* get to be an expert about what I should or should not be seeing through *my* telescope, through *my* eyes, through *my* observing conditions?


Edited by CrazyPanda, 21 October 2020 - 08:01 AM.


#66 happylimpet

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Posted 21 October 2020 - 10:48 AM

A lack of an observation of something you were trying to observe is a a valid observation in itself.

Why is it that *you* get to be an expert about what I should or should not be seeing through *my* telescope, through *my* eyes, through *my* observing conditions?

 

Valid, but it carries little weight as there could be all manner of reasons why you didnt see it. You might have got the date wrong on the simulator. You might have forgotten to flip the simulation. There might have been a dead fox in the telescope.

 

You might have failed to see it for any number of reasons. Therefore I dont think your failure to see it should be taken as a rock solid data point. Not compared to those who have seen it. I'm surprised you find this contentious.

 

Im off to start a thread about how best to climb K-2 based on the fact ive never done it. So that applies some quite useful contraints, doesnt it?


Edited by happylimpet, 21 October 2020 - 10:49 AM.


#67 Pcbessa

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Posted 21 October 2020 - 01:12 PM

Crazy Panda, I think you still have to try a few more nights. Eventually you will spot Deimos in your 15".

Most nights I do not see Deimos, though for some funny reason I tend to catch Deimos at maximum elongation. This is when seeing is average (which means not so good in Scotland) If seeing is good (needs specific weather conditions such as a blocking high and a stable atmosphere), then Deimos is "easy".
I mean in those nights I could even see it on and off without Mars being hidden.

Phobos is downright difficult for my 10" (I had only a suspected glimpse in one good night after long waiting) but perhaps I still need to try it under excellent seeing which is a rarity at this time of the year in Scotland.

To give an example, last 7 nights have seen consistently heavy rain. Not a single glimpse of sky. By December the weather usually becomes better here but by then Mars is already much further from us and Phobos will be probably impossible in my 10" aperture.

#68 Pcbessa

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Posted 21 October 2020 - 01:16 PM

And the only reason I can think for your observations Crazy Panda is if in those 3 nights you spotted Phobos, you catch Deimos always closer to Mars. If both are near Mars, Phobos is technically easier to see and Deimos would be even harder to see.

I also experienced the weird phenomena in one the nights I saw Deimos at max elongation. Some clouds (thin stratocumulus) would dim Mars and strangely both features of Mars and Deimos became then more easily to see. This mirrors the reports here in the forum that smoke makes Mars and it's moons easier to see.

 

My sense is still that seeing (a stable atmosphere) seems to help with both Mars features and seeing it's moons. Same when Mars gets higher in the sky.


Edited by Pcbessa, 21 October 2020 - 01:18 PM.


#69 GeneT

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Posted 21 October 2020 - 04:57 PM

I had no idea that you could see the moons of Mars with a 12 inch telescope--under certain conditions. I wish I had known this years ago.



#70 Redbetter

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Posted 21 October 2020 - 05:06 PM

When someone describes Pickering 6 seeing in a 15" as "mediocre at best" and passes that off as a reason they don't see Deimos, it indicates a lack of realistic calibration/judgement of conditions, and the realization that their statement of conditions cannot be taken at face value.  (This is not unlike frequent Bortle scale & NELM discussions with new members where things don't in any way match up--after a few questions it becomes apparent what the conditions actually are.)  It also calls into question subjective claims of something being "easy" when one realizes that a person's evaluation of a known scale is so far off the mark. 

 

Then there is the experience side of things, weighing a few non-sightings by one individual (at least one non-sighting was in a period in which Deimos was poorly placed) vs. folks who are actually catching Deimos regularly with 8 to 10", not to mention Allan's sighting with 130mm.

 

When someone continues doubling down on a bad position, dismissing all explanations and making easily refuted claims about the theoretical and practical aspects, it becomes apparent that reason and logic are no longer part of the discussion.  There is too much emotional investment at that point, which clouds judgement.  As per my sig:  "Reasoning will never make a man correct an ill opinion, which by reasoning he never acquired." Jonathan Swift



#71 Redbetter

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Posted 22 October 2020 - 03:24 AM

Okay, had elongation occurring for both moons on opposite sides of Mars tonight and was stuck in the backyard due to smoke haze that keeps hanging about.  So I brought out the 25 year old 8" SCT (not the 20" with an 8" mask) to see if I could bring in either/both of the moons.  Spoiler #1:  yes, I got both of them.  Spoiler #2:  Deimos was far less difficult and certain.  However both were difficult and only seen when using the occulting bar (actually some extremely thin blackened copper wire that is a little greater than a Mars diameter wide at opposition.)

 

Conditions:  The weak smoke haze and mild temps made for relatively stable skies for a few hours.  However, this was in the suburbs and the poor transparency resulted in 18.2 MPSAS overhead.  In the 8" SCT this was perhaps as good as Pickering 7 early on or in the best moments, declining to Pickering 6 as a slight breeze started late in the session (about the time I turned to a star to do the seeing rating), and was down to about a 5 when I packed it in.  (This sort of decline has been about the norm with these smoke haze moderated conditions.)  

 

I had let the scope sit out for about an hour to thermally acclimate.  I used a 9mm T6 Nagler with 2" TV mirror diagonal for about 244x initially.  Looking at Mars unfiltered showed that the conditions were not perfect, but were good enough for the attempt.  I had no luck on Deimos (Phobos was far too close) so I switched to the 7.4 TV Plossl with occulting bar (~297x.)  After getting best focus dialed in and experimenting with the best orientation, I picked up Deimos at 11:35 PM, (6:35 UTC 10/22/20), at about 58 arc seconds from the planet's surface (per Stellarium measurement.)   After a time and as I had begun searching for Phobos, I found I could frequently hold Deimos continuously.  It was indirect only in these conditions, but it could be found.

 

I badly wanted Phobos, but initially it was only about 10-11 arc seconds from the planet and completely invisible in the wide glow around the planet, even with the occulting bar blocking Mars' disk.  I kept trying and rechecked positions with Stellarium as it passed 12 and 15 arc seconds separation.  There were a few times I caught a weak glint at ~15 arc seconds, but I never could relocate it in a reasonable window to confirm.  I changed the occulting bar orientation somewhat, experimented with direct and indirect searches, etc. but there was just too much glow in the way.  I had some more hints off and on as time progressed, and kept experimenting with the occulting bar angle.  Finally, at 18 arc seconds separation at 7:22 UTC 10/22/20 I was able to get a series of locks on Phobos.  After that I could find it frequently, although still far more difficult than Deimos which had widened to about 61 arc seconds.  Phobos had been quite a challenge.   I did some rechecking with the 9mm and a 7mm with no occulting bar, but had no hints of either moon this way.  



#72 Pcbessa

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Posted 22 October 2020 - 01:01 PM

RedBetter your observations mirror mines with a 10" Dob, in a striking similar way. I used also a Barlowed Nirvana 7mm for 350x. My skies are however considerably darker than yours. I think the difference is that I could see sometimes Deimos without the occulting bar (it's a larger aperture so that's expected) and I didn't spent as much time as you did with Phobos, so my observation of Phobos was only a "weak glint" as you mentioned first.

#73 Allan Wade

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Posted 24 October 2020 - 12:39 AM

I had no idea that you could see the moons of Mars with a 12 inch telescope--under certain conditions. I wish I had known this years ago.

I think it’s quite amazing what is observable in amateur telescopes. I’ve come to realise what is written in most texts is probably aimed at your average level observer. No doubt many exceptional authors are probably not themselves exceptional observers, and telescope aperture required to see objects is largely overstated. That’s why I like to read first hand references of what experienced observers have achieved.


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