The Crescent nebula had
long been an object of my desire. This faint, arcing diffuse nebula
appears in one of the most beautiful fields of the summer Milky Way,
about 2/5th of the way from Gamma to Eta Cygni. Catalogs list it as
10th magnitude but I found it to be much more difficult than this
would imply. 
The
above color image was created by combining red and blue
second-generation DSS images.
I tried and tried one year to see the Crescent in my 6-inch f/8 to no avail.
When I finished my 18-inch f/4.5 Dob, this was my first
serious target. I was rather disappointed when I failed to see the
nebula with my new scope on several different nights. Since then Skyhound
18 and I have gotten to know each other much better. We've
successfully observed some very faint objects. On the night of May
30/31 I was very, very careful with my dark adaptation and
conditions were quite good. I believe that it was my experience with
the scope and the confidence this brought that made the difference
in my eventual success.
This nebula makes an
arc among several bright stars. I was able to detect the nebulosity
on the northeast side first. Eventually I found the curving haze to
the southwest. With time and averted vision I was able to make out
the entire arc of the nebula.
One July I had
the pleasure of observing NGC 6888 with Kemer Thomson's 18-inch
Obsession from Mount Laguna. At the time he had an advantage over
me: a wider field eyepiece. The wider field made a big
difference. The elongated white
area near the center-top of the image above was clearly visible much
as it appears in the image. Filters made an even bigger difference. With a UHC filter the rest of the nebula
appeared, looking very much like the image (without the colors). The
best view was with the OIII filter which greatly increased the
contrast. With the OIII in place the faint wisps in the center
filled the nebula into a complete "pear."
Without a filter it is
essential to observe this object with a wide field eyepiece.
The field in a
12-inch LX200 with a Widefield 40mm eyepiece (76x).
A UHC or OIII filter
may be necessary to view this nebula in scopes smaller than 8-10
inches. AJ Crayon writes, "In my 8 inch f6 at 60X the nebula
was about 15'X5' in a northeasterly PA with a larger northeastern
side. On this particular night the nebula was of uniform
brightness and the famous crescent shape appeared pear like with
several stars involved. Yes, pear like!"
Don Pensack writes:
Appeared
"ear-shaped", relatively bright, no filter necessary at
~200x. Brightest section appeared to be the Ear outline, with
10-20 irregular tufts of nebulosity scattered across the face.
A much fainter outline completed the "pear" mentioned.
With a UHC filter, the lines resolved into intertwined filaments
similar to the Veil Nebula, though the particularly abrupt
reduction in the number of field stars made the sight less
pleasing. With the UHC filter, the general outline became
sharper, and the filaments seemed to "writhe" across the
field as even fainter nebulosity came in and out of view. I've
seen this object in 6", but the amazing amount of detail
visible in 20" makes this up there with the Veil as a
"showpiece".
In
smaller instruments this is a challenging object to detect.
But in larger scopes the Crescent becomes a showpiece, particularly
when an OIII filters is employed.
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