Thanks for choosing to highlight this excellent HII region. I know I haven't given it the attention it really deserves, but here are some of my notes --

18" (8/23/03): this is a beautiful object with a 31mm Nagler and OIII filter, reminiscent of one of the sections of the Veil as viewed in a small scope. The main N-S shallow arc, convex to the east, spanned a large percentage of the field. At the south end, the strip widens and is less distinct although it contains the bright knot LBN 537 = Sh 2-157a, surrounding a mag 11 star (easy without filter). A much fainter western section (roughly 20' W) also extends N-S, passing through a scattered group of stars. At the south end it appears to merge with the eastern branch.

17.5" (10/17/98): surprisingly easy, huge HII region at 100x with OIII or UHC filter. Appears as a faint, curving graceful arc, very elongated N-S and bowed out on the following side. Extends north and south of open cluster Markarian 50 which is off the west side. Appears up to 35'x8' in size with the brightest section (near Mrk 50) showing subtle structure. The bright knot Sh 2-157a = LBN 537 is situated beyond the southern end of this arc. The illuminating star is HD 219460 = WR 157, the brightest member of Mrk 50, and this object is listed as a probable Wolf-Rayet shell in ApJ, 252, 1982.

Sh 2-157a = LBN 537 was picked up at 100x as a faint, ill-defined glow surrounding a mag 11 star with a couple of fainter stars possibly involved in the nebulosity. Good view at 105x (19mm) using an H-Beta filter which dims the illuminating star. The nebulosity appears circular, fairly crisp-edged, ~2' diameter. At 220x without a filter, the diameter increases to nearly 3', although the edge blends into the general haze of the huge HII region Sh 2-157. The central star has a mag 13.5 companion close NW.

Using 220x, Mrk 50 resolved into about 10 stars within a small semi-circle. The brightest star has a very faint and close companion close following. There is a very small distinctive group of four stars within the semi-circle consisting of two mag 12.5 stars with mag 14-14.5 companions about 10"-15" south.

17.5" (11/30/91): at 100x and OIII filter; moderately bright, very large, elongated ~2:1 N-S, ~25'x10'. The brightest region is widest and shows subtle structure and brightness variations. Appears slightly fainter as extends in a lane to the NNE with a smaller extension to the south. A compact open cluster, Mrk 50, is nestled along the west edge of the center of the arc.