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Ring Nebula


mikeDnight

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A few days ago a friend gave me a 4mm 82° eyepiece as a 'thankyou' for me making him a Mars globe based on my own observations. Last night was the first reasonably clear night I've had since I received the eyepiece so i thought I'd try it out. I'm my little Tak the Nirvana is sharp right across the field. Saturn remained in focus as it left the field of view which impressed me considering the low price of this make of eyepiece. 

I wanted to find out if the Nirvana would deliver as well on light transmission as it did on sharpness, so i aimed the scope at M57 to see if I could see the 13.2 magnitude star that's situated on its periphery. The star revealed itself with very little effort which pleased me greatly. The nebula itself was also pleasing and revealed some obvious variations in brightness hinting at its structure.  Field stars in the attached sketch are only approximately placed!

2017-07-10 08.54.37.jpg

2017-07-10 08.54.26.jpg

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Excellent sketches and observations Mike :icon_biggrin:

For quite a while I used a 4mm Nirvana as my high power eyepiece at that focal length and I was very impressed with it as well. I believe it is the same as the William Optics UWAN. Considering the number of lens elements and the ultrawide field the design does very nicely indeed as a high power occular.

Interesting about that mag 13 star just of the edge of the nebula. I see this star regularly and I have to say that I was surprised when I checked it's magnitude. I'd have said no dimmer than mag 12 but the published figures seem to agree that it's a whole magnitude fainter :icon_scratch:

 

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5 hours ago, John said:

Excellent sketches and observations Mike :icon_biggrin:

For quite a while I used a 4mm Nirvana as my high power eyepiece at that focal length and I was very impressed with it as well. I believe it is the same as the William Optics UWAN. Considering the number of lens elements and the ultrawide field the design does very nicely indeed as a high power occular.

Interesting about that mag 13 star just of the edge of the nebula. I see this star regularly and I have to say that I was surprised when I checked it's magnitude. I'd have said no dimmer than mag 12 but the published figures seem to agree that it's a whole magnitude fainter :icon_scratch:

 

Thanks John, :happy11:

If I remember rightly, some time around 2003 Flagstaff made a study of the magnitudes of stars using photoelectric photometry and found that the previous magnitude estimates were, in many instances, a long way from being accurate. I seem to remember the star on the periphery of M57 was thought to be in the region of 11th mag, but previous estimates were based on photographic plates and were found to give a false impression. The central star was thought to be mag 13 but was later found to be mag 15. I've never seen the central star! Perhaps the 13.2 mag star is relatively easy to see because its close to the ring, but whatever the reason its a nice test for seeing and telescope. :icon_cyclops_ani:

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There are so many magnitudes to choose from: photographic (more sensitive to blue), visual, bolometric, and quite a few more, you need to be very careful comparing tables. I would be very surprised to see a mag 13.2 (visual) star in a 4" instrument, unless my skies had a NELM of 6.5 or better, although the dark background at such a small exit pupil definitely helps

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It surprised me as well Mike when I first learned about the more accurate modern magnitude survey, to find that my scope back then, which was a FS 128mm, could reach mag 13. Up until then, it was my understanding that 150mm was needed to reach down to mag 13. However, reading Leslie Peltiers Starlight Nights, it appears a 6" scope can under the right conditions, detect the central star at mag 15.2 or fainter, so for a 100mm to reach mag 13 shouldn't  be too difficult to believe. It has to be said however, that although I feel the star is obvious, it isn't easy, as it flickers in and out of existence if the seeing is turbulent.

My position of the star on my sketch is different from the attached image as I used a prism diagonal!

Screenshot_2017-07-10-11-43-46.png

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Back in the 80's I was actively involved in visual SN search, checking and validating the search charts for Thompson's "SuperNova Charts"

I was using a 12.5" f5 (visually) just 10 km north of Melbourne (3 million pop.) I could regularly get down to 15.5 mag.

Those were the days........

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Much depends on the observer. I remember spotting the Antenna Galaxies with my C8, and only one of the others present could spot them (in the right location). In my (fairly dark) suburban garden I have gone down to mag 13.9 on OJ 287 (my most distant object yet, at around 3.5 billion lightyears away). From a really dark site with transparent skies I should be able to gain at least a magnitude more, but the fairly bright background of the centre of the Ring Nebulae makes the central star very tricky indeed. I have seen it, but that was with Olly's 20" Dob (Sir Isaac).

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I have glimpsed the central star of M57 with my 12" dob but only occasionally and I was not able to "hold" the star with direct vision.

That chart of the star magnitudes in and around M57 is useful - thanks Mike :icon_biggrin:

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I agree about the image of this 4mm Mike. I was surprised how good the star image of Arcturus was when you let me look through it.  Text book, and as you say, right across the field.

Alas, for this speccy type  it was very difficult to use because of the eye relief, and I could only see a small part of the field at any one time. For those without specs  or folks who are not concerned by it, it's extremely good value.

Mind you Mike, I think you would have produced just as excellent a drawing almost whatever eyepiece you were using :smile:.

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