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mikeDnight

Pleiades nebulosity

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I've just come in from a brief session observing the Pleiades. While waiting for my scope to become thermally stable, so as to try out my new 2mm Vixen HR eyepiece,  I thought I'd spend the time taking in some low power vistas. Turning my 100mm F7.4 onto M45 I thought I'd try a few different powers to see which gave the most obvious view of the nebulosity. My first choice was my Baader 35mm Eudiascopic giving me a power of X21 and within only a few seconds, so not properly dark adapted, the entire cluster showed itself to be bathed in a swath of subtle nebulosity. Using averted vision the nebulosity appeared both obvious and easily visible. Replacing the 35mm with an 18mm Ultima, giving a mag of X41, the vastness of the nebulous cloud was lost. Instead, the Merope nebula became the most visible component of the cloud, again an easy and obvious catch in the 100mm. Once I increased the power to X185 using a 4mm Nirvana, several but not all the stars displayed some nebulosity. 

I've observed this nebulosity many times but never paid any attention to which magnification gave the best views. And, although I've sketched the complexity of this nebula at medium powers in the past,  after being thoroughly dark adapted, I have to admit the low power casual view I had tonight was quite surprising. I was on the verge of starting a low power sketch but snow clouds moved in to spoil my enjoyment. This will hopefully be a subject I'll return to asap!

It would be nice to hear of the experiences other observers have had with the nebula, and what magnifications work best with your scopes. 

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I think you are very lucky Mike, I have spent long sessions on M45 at dark sites with my 18" dob and have only been able to observe precious little nebulosity, compared to what I know is there via my imaging sessions. The brightest patch of fuzz is around Merope but I have always found it difficult to make out any real form or substance other than something that looks like a dewed eyepiece on a bright star. There are a couple of bright flecks that show well in images but I have never been able to observe them visually. In fact, I commented about the disappointing views to another seasoned observer with his 24" dob and his experience was pretty much the same. My 35mm Panoptic gives just over 50X and 21mm Ethos gives about 80X.  

Maybe the quality of the sky is important, when imaging, reflection nebulosity always shows up as more defined on the most transparent nights.

One thing I do enjoy following is the "seagull in the distance" shaped line of stars that are adjacent to the cluster, and their various hues, I especially enjoy the golden stars there.

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Great post. ? I rarely get the chance to see the nebula here, except at my dark site and even then needing good transparency. I’ve found low power works best - I’ve not see any hard edges to latch onto at high power and just find myself looking through it. Even binos showed it nicely on one occasion. The Pleiades is one object that I really really wish was closer to the images through the eyepiece.

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In the early days of my astronomical interest it was generally accepted that photography was the only medium that would show nebulosity round stars of the Pleiades. Nowadays, almost anyone with good seeing conditions and a small high quality refractor seems to be able to detect it visually. Most of the times that I've "seen" it, I used to put it down to moisture in the air or on the objective, the predominance of nebulosity round Merope I put down to its greater brightness, in such conditions I have seen similar appearances around other bright stars. And yet, at other times nebulosity has looked quite convincing. I read some time ago that the nebulosity is a line of sight association with the Pleiades cluster and the stars were gradually passing through it.   ?

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Hi Mike, I prefer low power views in my widefield scopes, using the 24 ES 68 in the H130, the 20mm Lunt HDC/Nikon 17HW in the 200mm f3.8 and the 20mm Lunt in the 10" f4.8 on the Pleiades. The Merope itself takes more mag and I'll use the 14mm HW and the 12.5mm Docter UWA on it, even in the 15". Glad to see you are taking some time to view this object.

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21 hours ago, mikeDnight said:

I've just come in from a brief session observing the Pleiades. While waiting for my scope to become thermally stable, so as to try out my new 2mm Vixen HR eyepiece,  I thought I'd spend the time taking in some low power vistas. Turning my 100mm F7.4 onto M45 I thought I'd try a few different powers to see which gave the most obvious view of the nebulosity. My first choice was my Baader 35mm Eudiascopic giving me a power of X21 and within only a few seconds, so not properly dark adapted, the entire cluster showed itself to be bathed in a swath of subtle nebulosity. Using averted vision the nebulosity appeared both obvious and easily visible. Replacing the 35mm with an 18mm Ultima, giving a mag of X41, the vastness of the nebulous cloud was lost. Instead, the Merope nebula became the most visible component of the cloud, again an easy and obvious catch in the 100mm. Once I increased the power to X185 using a 4mm Nirvana, several but not all the stars displayed some nebulosity. 

I've observed this nebulosity many times but never paid any attention to which magnification gave the best views. And, although I've sketched the complexity of this nebula at medium powers in the past,  after being thoroughly dark adapted, I have to admit the low power casual view I had tonight was quite surprising. I was on the verge of starting a low power sketch but snow clouds moved in to spoil my enjoyment. This will hopefully be a subject I'll return to asap!

It would be nice to hear of the experiences other observers have had with the nebula, and what magnifications work best with your scopes. 

It's interesting to read what Wikipedia.org has to say about the nebulosity that surrounds the Pleiades (M-45).....>

"The cluster is dominated by hot blue and luminous stars that have formed within the last 100 million years. Reflection nebulae around the brightest stars were once thought to be left over material from the formation of the cluster, but are now considered likely to be an unrelated dust cloud in the interstellar medium through which the stars are currently passing"....> https://en.wikipedia.org/wiki/Pleiades

Klitwo

 

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The only time I can be confident of seeing the nebulosity was when using my 20x80 binoculars. 

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Thanks for your replies gents,

Looking at Walter Scott Houston's DEEP SKY WONDERS, the author mentions on page 263 that the German astronomer Wilhelm Temple reportedly observed the nebulosity surrounding Merope using a 4" refractor in 1859. Walter S Houston mentions that his 4" refractor showed it readily, yet his 10" reflector failed. He goes on to say that a 5" Apogee telescope succeeded, and a 6" reflector readily showed it too. It was also observable without averted vision in a 16". Intererestingly, O'Meara notes in his book The Messier Objects, that Lewis Swift saw it in a 2" refractor at 25X and that the great double star observer S. W. Burnham could not see it in an 18" refractor.

It seems that increased aperture may not be the way to go for getting the best from this nebula on an average night, but there does seem to be an increased chance of catching a glimpse of it more easily in smaller scopes with low powers and reasonably wide fields. Curious!

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Is this another "ashen light" type observation target I wonder ?

https://britastro.org/node/13867

For what it's worth I have observed what I have taken to be nebulosity around the brighter stars of the Pleiades group quite often with my scopes. Usually the effect is more noticable at lower powers.

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I have always found it a little puzzling that some seasoned observers seem so doubtful about the visibility of nebulosity around the Pleiades.  Generally, though I have owned and used many scopes greater than six inches over the years, most of my telescopes have been between three and six inches.  I like nice quality optics which can easily give fields of 2 degrees or more because I particularly like looking at extended objects and wide field views of star fields, asterisms and open clusters.  With dark and transparent skies I find the nebulosity fairly easily visible more often than not in scopes between 3-6 inches.  To me it is very different from 'false' nebulosity seen surrounding stars when seeing conditions are affected by moisture in the air and misting on optical surfaces.    In addition the nebulosity around some members of the Pleiades has regular structure, very different from the 'false' nebulosity seen around stars in damp observing conditions etc.   For any competent observer using 3- 6 inch aperture scopes on the Pleiades on a good night at the Kelling Autumn star party, I would be very surprised if they couldn't see the nebulosity.  I do tend to use refractors as I find them mostly to have better contrast than other telescopes and I'm also a keen planetary and Lunar observer so my scopes have to be of good optical quality.

 

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Nice report Mike, it seems the skies have been veru transparent simce thw rains washed them clean; Paul's HH and your M45 nebula observation seem to back this up. I'm sure transparency is the key.

I'm still, unfortunately in the not seen camp, or at least only seen when my objective is dewed up! Thats probably because most of my observing is do e under fairly poor skies so I don't get much chance under skies which are dark enough.

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On an average night, NGC 1435, the Merope nebula within the Pleiades will not necessarily be seen at any aperture whether refractor or reflector. Within a period of good transparency at a dark sky location at low power wide or ultra wide field, with for instance a dobsonian, associated nebulosity, particularly the Merope is quite impressive and can be expansive. I have not so far seen the Merope nebula in my TV85, which had been set up alongside my 8" dob, during a session where the dob did reveal the nebula, I will keep trying as it should be quite probable in the right conditions. The best encounter has been with my 14" dob on a transparent night, SQM-L:  21.3, x52, 1.59 degree field. The Merope nebula encompassed a vast field, further reflection nebula including NGC 1432 The Maia apparent. In both my 8" and 14" dobs, the Pleiades bubble, streaks of nebulosity surrounding the cluster can be comprehended (low power 1.75 to  just over 2.00 degree field).  

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3 hours ago, paulastro said:

 I do tend to use refractors as I find them mostly to have better contrast than other telescopes and I'm also a keen planetary and Lunar observer so my scopes have to be of good optical quality.

 

It would be interesting to understand more in terms of this aspect with regard to reflection nebula associated with M45. The Merope nebula for example is very subtle and faint, invisible as far as I am aware in filter assisted observing, I am not sure how much contrast is a key element to this observation? Certainly the mirrors in my two dobs yield good contrast and are of a high quality figure, yet my TV85 at low power is more contrasty and commanded a beautiful image and pleasing composition on the Pleiades. However there was not an indication of nebula on this occasion compared as mentioned with my 8" dob. Therefore in a dark transparent sky, a large exit pupil, perhaps a slightly grey background serves more this reflection nebula? Interesting to hear your thoughts. 

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45 minutes ago, scarp15 said:

It would be interesting to understand more in terms of this aspect with regard to reflection nebula associated with M45. The Merope nebula for example is very subtle and faint, invisible as far as I am aware in filter assisted observing, I am not sure how much contrast is a key element to this observation? Certainly the mirrors in my two dobs yield good contrast and are of a high quality figure, yet my TV85 at low power is more contrasty and commanded a beautiful image and pleasing composition on the Pleiades. However there was not an indication of nebula on this occasion compared as mentioned with my 8" dob. Therefore in a dark transparent sky, a large exit pupil, perhaps a slightly grey background serves more this reflection nebula? Interesting to hear your thoughts. 

Well, I'm not sure where you get 'slightly grey background' from?  My 102mm refractor has a focal length of 709mm.  Using my 17'5mm Morpheus gives a magnification of x40.5.  Dividing 102 by 40.5 gives an exit pupil of 2.5.  I wouldn't consider this is a large exit pupil for the aperture, and in the dark skies of Kelling (where I've had my best views of the Pleiades associated nebulosity) the view with this telescope and eyepiece is extremely dark and contrasty.  I'd certainly expect a comparable view if I were able to use your TeleVue 85 at Kelling with an appropriate eyepiece.

To be honest, I don't generally observe the Pleiades with large apertures, or at least I haven't for a good long time - mainly because I prefer a view where I can see all the principle stars.  If I remember to do it, when I go to Kelling this Autumn, I will make sure I do some experiments with larger apertures.  If I do, I'll be pleased to post up my findings. :smile:

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15 hours ago, scarp15 said:

a large exit pupil, perhaps a slightly grey background serves more this reflection nebula?

Ah, a great observation from a seasoned observer!:thumbsup:

Your comment is a reflection of you being fully dark adapted, exactly as I see the sky through large exit pupils or naked eye once dark adapted- it looks grey and this level of adaptation really helps seeing the Pleiades neb and others.

From Vogel

 

"All cats are gray in the dark

An astronomical view on the physiology of vision

eye.jpg

 

If you search the astronomy related internet forums about vision and in particular dark and light adaptation and its relation to deep sky observing, you will find the wildest theories. What precisely is rhodopsin and what does it do? How does vision at night differ from that at daylight? What is dark adaptation and why does it take so long? And how is this all connected to red light?

During my time as a researcher at the University of Freiburg, I worked for many years as a physicist with spectroscopic methods on the activation and deactivation processes of rhodopsin (here is list of publications of that time). For our annual Deep Sky Meeting 2012, I put together in talk those topics on vision that I felt the most important for us visual observers. In the following three part essay, I would like to present the essentials of that talk.

 

part 1

Rhodopsin activation"

 

 

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I had a go at this tonight with my 12 inch F/5.3 dob.

24mm Panoptic = 66x / 4.5mm exit pupil and there was no obvious nebulosity around the stars. Pitch black background sky.

21mm Ethos = 76x / 3.96mm exit pupil and still nothing other than the "diamonds on black" effect.

31mm Nagler and 30mm Aero ED = 53x / 5.66mm exit pupil = smudges of ill-defined something around Merope and some of the other brighter stars in the group. Background sky dark but not pitch black.

40mm Aero ED = 40x / 7.5mm exit pupil = slightly more obvious but still ill-defined smudges as above. Dark grey rather than black background sky.

Also tried Capella and Rigel as comparisons and did not see anything that resembled nebulosity around them with any of the eyepieces above.

So there you have it (but I'm not sure what :rolleyes2:).

 

 

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10 hours ago, John said:

I had a go at this tonight with my 12 inch F/5.3 dob.

24mm Panoptic = 66x / 4.5mm exit pupil and there was no obvious nebulosity around the stars. Pitch black background sky.

21mm Ethos = 76x / 3.96mm exit pupil and still nothing other than the "diamonds on black" effect.

31mm Nagler and 30mm Aero ED = 53x / 5.66mm exit pupil = smudges of ill-defined something around Merope and some of the other brighter stars in the group. Background sky dark but not pitch black.

40mm Aero ED = 40x / 7.5mm exit pupil = slightly more obvious but still ill-defined smudges as above. Dark grey rather than black background sky.

Also tried Capella and Rigel as comparisons and did not see anything that resembled nebulosity around them with any of the eyepieces above.

So there you have it (but I'm not sure what :rolleyes2:).

 

 

Great observation and description John.

I bet you feel much better now you're confident about the uncertainty! Your observation just goes to illustrate how wraith like this nebula can be. Did you notice any perceivable difference in the darkness of the sky background away from the cluster? 

Edited by mikeDnight
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1 hour ago, mikeDnight said:

Great observation and description John.

I bet you feel much better now you're confident about the uncertainty! Your observation just goes to illustrate how wraith like this nebula can be. Did you notice any perceivable difference in the darkness of the sky background away from the cluster? 

The sky away from the cluster exibiting similar variations in blackness as I switched between these eyepeices on other targets Mike.

Usually my eyepiece of choice for faint fuzzy hunting with my dob is the 21mm Ethos because it shows a lot of sky, has a reasonably efficient exit pupil and shows a dark background sky. The longer ones generally get used with my refractors. But for the Pleiades nebulosity, I think changing the habit works best :icon_biggrin:

Nicely illustrates why we should not get too set in our ways !

 

 

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On ‎29‎/‎01‎/‎2019 at 23:37, paulastro said:

To be honest, I don't generally observe the Pleiades with large apertures, or at least I haven't for a good long time - mainly because I prefer a view where I can see all the principle stars.  If I remember to do it, when I go to Kelling this Autumn, I will make sure I do some experiments with larger apertures.  If I do, I'll be pleased to post up my findings. :smile:

Thanks, if you are able to gain some time on the Pleiades at Kelling and provide some feedback in due course, that would be welcome.

Last night, I was able to go observing with my TV85 and 14" OOUK dob. My intention was to capitalize on using the largest exit pupil I have available. Therefore I refrained from using a paracorr in the dob, retaining F4.6 focal ratio. A 31T5 provided x52, 1.59 TFOV, 6.7mm exit pupil. The TV85 this equated to x19.4, 4.24 TFOV, 4.4mm exit pupil. Clearly the dob had the advantage in terms of exit pupil. Transparency was good but not excellent, SQM readings varied between 20.96 to 21.1, short by a margin based on this location. However showpiece objects such as the Orion Nebula and M35 were exceptionally presented and as is often the case, transparency conditions varied slightly throughout the course of the session. I also returned repeatedly to M45 throughout the night, taking advantage for its southerly position.  

In the dob the image scale is fine for gently nudging slightly and the Merope nebula was disenable and quite expansive with direct vision. It was though subtle and faint, nebulosity overall diminished compared to previous observational occasions. As with other certain faint and very subtle objects, it becomes easier to visualise once accomplished and repeated on successive outings. The TV85 however was unable to detect any nebulosity. 4.4mm exit pupil being perhaps a disadvantage. If Id kept hold of my TV76, F6.3, this may have faired better. A few years ago, I used a 35mm Panoptic this might have worked. Therefore a large exit pupil to draw out this faint subtle reflection nebula is preferable unless perhaps transparency is excellent. 

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