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A Sharpless Treasure Box

The Sharpless 254, 255, und 257 Trio


 16. Januar 2010

Last night, we had one of these rare nights where everything was right. Schauinsland Mountain at 1200 m in the Black Forest was above the low winter clouds, which covered everything with a thick blanket. It was cold, but not windy, Seeing was acceptable and transparency was excellent down to the horizon. Despite the cold in January, it became a long observing night together with Thomas until 4 in the morning and in particular my H-Beta filter saw really a lot of photons. The highlight of the night was, however, a group of Sharpless Nebula in Orion.

POSS II Composite

The group to the right comprises from left to right Sharpless 255 and Sharpless 257 as quite compact HII regions and Sharpless 254 as a somewhat more diffuse object to the right (Sh257 corresponds to  IC 2162). Further, there are the smaller objects Sharpless 258 and 256 somewhat offset to the bottom. The entire group is located at the Gemini/Orion border. A pdf file with finder charts is here.


In the 24 mm eyepiece of my 22-Inch Dob, the two more compact nebula 255 and 257 were easily visible with H-Beta filters as milky, well defined areas, each surrounding a star in the middle. Sharpless 254 was somewhat more diffuse, but could be seen without retinal torture. The entire group fit into the field of view of the eyepiece and the contrast between the diffuse 254 and the more compact 255 and 257 was particularly beautiful. Thomas baptized the group "The Three Snowballs".

With the UHC Filter, all three were still visible, yet much more difficult than with H-Beta. As to be expected for low-excitation HII regions, they were not visible with the OIII filter.

After I had enjoyed the view of the group for some time, I shortly tested the small nebula Sharpless 258, which is to the left on the image. As there was nothing visible immediately, I did not try to push this, in particular as there are superimposed stars, which might be deceiving.

Sh256, on the other hand, was well visible as a separate glow detached from the main mass of Sh257.

POSS II Composite

The three brighter nebula of the group are certainly also accessible with smaller scopes. An H-Beta Filter or at least a UHC filter are mandatory, however.

By the way, three degrees to the north there is bright Sharpless 252 (Monkey Head Nebula) around Open Cluster NGC 2175, which is considerably more conspicuous and larger and responds very well to the OIII filter.

Steward Sharpless' catalog of HII objects is not really mainstream for visual observers. Except for the brighter members, which are also covered by the Messier catalog or NGC, there are not that many observing reports of Sharpless objects.  For me personally, the Sharpless Catalog is a treasure box of unknown and nevertheless very interesting objects.

For those interested in exploring Sharpless objects, there is an impressive collection of H-alpha and narrow band images by Dean Salman on Comprehensive information on the single objects can be found on Kevin Jardines website

Here is Thomas' observing report of that night.

And here is my own Sharpless Observing Atlas.

Image credit: DSS