Sh2-261 (Lower's Nebula)
RA 06 08 56.6
Dek +15 48 07
type: Emission Nebula
Sharpless 261 aka Lower's Nebula at the Orion/Gemini border is an object for the evening, that has now already passed the meridian when it turns dark.
DSS image of Sh2-261
There are several good images of this HII region, which lends in particular for narrowband imaging as it has lots of structural details in the different emission lines. Below is an image by Dean Salman in SII HII OIII (http://www.sharplesscatalog.com/Shar...aspx?Sharp=261)
Despite that Sharpless 261 looks spectacular and bright on narrowband images, it is not an easy visual object and there are not that many observing reports of this large HII region.
My first observation of Sh2-261 was in 2010 during a sub-par night with my 22" Dob and my Panoptic 24mm, yielding an ep of 5.3mm. With OIII filter I could see a very difficult glow around the central area of the object, and a vague glow with the H-beta filter, of which I was not fully sure.
One year later, in 2011, I re-visited this object under excellent skies, again both with OIII and H-beta filtering. This time, the visibility of the nebula was much better. Still, it did not really jump at you. With the OIII filter, I was able to pick up the central region of the nebula, corresponding to the lower part of the OIII emitting region in Dean Salman's image above. Below is a DSS red print of the nebula with a central star pattern being marked, that helps identifying the field.
With the H-beta filter, this central part is lost and other regions of the nebula become faintly visible. This is in particular a region south of the central region, which appears as the brightest and most structured part in the DSS image. Another more extended region was barely detectable NE of the central part. Both regions are marked in the DSS image above.
Despite appearing bright and distinct on narrowband images, this is a very faint nebula, that required good conditions and some patience to reveal its details. Hence, it is one of these "prototypical" Sharpless regions that I love so much :-)
Give it a go and let us know!
Good luck and great viewing!