A 360-degree panorama from the U.S. Naval Observatory 61-inch telescope dome catwalk, stitched together from nine photos. (You’ll notice I caught the catwalk railing in one of the photos. Oops.) This was on 2015-11-06, with a Canon G3 X.
Probably the best way to view (and download) the full-resolution version of this 23,890×2,597 image, which has such an extreme aspect ratio, is to use the Google viewer (use the magnifier): https://goo.gl/RTXJxp. The version below is 1/6 resolution. (After clicking to enlarge, right-click and open in a new tab to view the 1/6-resolution version.)