Cr 21, immediately to the south of IC 1731, is a distinctive 5' group of 10 brighter mag 8.5-12 stars, including ∑172, a mag 10 pair at 18" separation. The brighter stars form a rough semicircle open to the east with five fainter stars bringing the total to ~15. Visually, the collection appears similar to an asterism and Skiff reports that based on the color-magnitude diagram and proper motions, these stars are apparently unrelated.

Isaac Roberts discovered IC 1731 photographically on 29 Nov 1896 with his 20" reflector from his Starfield Observatory in England. He described it (AN 3429) as "Faint; elongated south following to north preceding; faint stellar nucleus; probably a spiral; cluster of stars 9 to 15 mag on the south side 13" following the nucleus."

400/500mm - 17.5" (12/11/99): very faint, fairly small. Appears as a low surface brightness glow elongated 3:2 WNW-ESE. IC 1731 is located 34' SE of NGC 672 and 5' N of Collinder (Cr) 21.

Notes by Steve Gottlieb