In northeastern Taurus, there lies a huge supernova remnant that's so faint and difficult to observe that many amateurs don't even know it exists. It's Sharpless 2-240, also known as Simeis 147. I spent about an hour exploring this sprawling nebulosity. At first, I used the spiral search feature of the ServoCAT to guide the 18-inch Obsession in circular sweeps around the sky. Observing at 109X (22 Nagler T4 w/ visual Paracorr) with an OIII filter, large patches of sheer nebulosity would pass through the ~45 arcminute diameter field of view. These were noticeable only because of the occasional patches of darker sky that confirmed the surrounding presence of faintly glowing interstellar gas.

I finally settled down to sketch a portion of this wispy complex centered on RA: 05h 37m 36s, Dec: +27d 06m 56s. The bright 5.9 magnitude star HD 37098 is positioned just inside the southwest field boundary in the above sketch. The subtly of this nebula is really astounding. I kept wondering, "Am I really seeing this?" Well, here's what my sketch records. Sh 2-240 runs helter skelter through the whole field. It appears brightest in the vicinity of HD 37098 and spreads in all directions from there. One bright patch, in particular, stands out. It's centered roughly at 05h 37m 16s, +27d 09m 40s, which is just north of a pair of 11th and 12th magnitude stars. Another branch extends north and east of HD 37098, reaching just beyond a trio of faint stars. Finally, there's a very subtle cloud along the northeast edge of the field.

Sharpless 2-240 is a challenging object requiring dark, transparent skies and reasonably large aperture. I'd be interested in hearing of other visual sightings of this ancient supernova remnant.