Cresent Nebula NGC6888

[ollypenrice]

Our last object of the night last night was the Crescent, very well placed. In the 14 inch SCT, unfiltered and with 26mm Nagler (134x) there was clearly faint nebulosity streaming through the field but, because it tended to become more visible as you looked away from it, defining its shape and structure was nigh-on impossible. Present but very elusive!

Putting in a Baader OIII filter was remarkable: instantly a clear crescent shape appeared looping around a bright triangle of three stars.

Imagers might wonder why this is called the Crescent because in its strongest wavelength, Ha, it is not particularly cresent shaped.  It's more like a Rugby ball, though one side is still fainter. However, imaged in OIII it changes dramatically, with a cling-film like layer engulfing the Rugby ball and, more significantly, a crescent-like outer shell appearing, most strongly in the lower right region as seen below.

 

So this is the 'crescent' in question. It was unmistakable at the eyepiece. A very rewarding object to observe and larger than I had expected, even though we were only seeing a smallish part of the whole of NGC6888.

It was discovered by Herschel in 1792, before OIII filters came along, so some considerable respect is due to the great man!

Olly

[John]

Lovely image and report Olly

I can see this object with my 12" dob at home but what I see is the more brightly illuminated curve of nebulosity with hints of the wider halo that it sits in. And it is more lilke the illuminated edge of a rugby ball as you say

I need to use an O-III filter to make the best of it visually although you can just about see it with a UHC. No filter = practically no nebula in sight though

 

[ollypenrice]

Just now, John said:

Lovely image and report Olly

I can see this object with my 12" dob at home but what I see is the more brightly illuminated curve of nebulosity with hints of the wider halo that it sits in. And it is more lilke the illuminated edge of a rugby ball as you say

I need to use an O-III filter to make the best of it visually although you can just about see it with a UHC. No filter = practically no nebula in sight though

 

At the moment I don't have a UHC. I had a Lumicon but one day I found that it's coatings had turned to powder and dropped off into the box. Given the price this threw me into a serious sulk and I never bought another one!

Olly

[estwing]

reminds me of a brain!

[scarp15]

Brain like yes, resembling a bit like a jellyfish I have in my notes somewhere, yet to observe it this season, hope my Lumicon coating OIII doesn't turn to powder any time soon.

[niallk]

Nice  I had one night of particularly memorably detailed views in my 15" with an O-III

[ollypenrice]

On 21/08/2017 at 21:56, scarp15 said:

Brain like yes, resembling a bit like a jellyfish I have in my notes somewhere, yet to observe it this season, hope my Lumicon coating OIII doesn't turn to powder any time soon.

As a precaution I now make ultra-sure that my filters are bone dry before storing them. I don't know if moisture affected my UHC but just in case it did I now take extra care.

Olly

[scarp15]

Yes good reminder Olly, for longevity filters, eyepieces etc need to be aired and bone dry before storage.

[swag72]

I hope that I need to take a trip up to see you soon and I hope that you will be able to interest me in some visual..... I am really fancying seeing what all the fuss is about ..... with the right toys of course!!!  

[MarkRadice]

Olly the crescent is fantastic but really benefits from a filter.  Here is how it looked through your 20" dob - with an Astronomik UHC filter.  A truly stupendous view.  They say you should not look through a telescope you cannot afford - or under skies that you don't get back home.  Your place ticked both boxes.

Clear skies,

Mark