NGC 4490 — Galaxy in Canes Venatici

NGC 4490, the Cocoon Galaxy, is a peculiar barred spiral in Canes Venatici, about 25 million light-years away, mid-encounter with its smaller companion NGC 4485 immediately to the north. The interaction has stretched both galaxies into elongated, distorted shapes and triggered intense star formation along the disturbed disks, with bright HII complexes scattered throughout NGC 4490's body. A faint cloud of HI gas envelops the entire pair like a cocoon, the source of the nickname. At magnitude 9.8 it is one of the brighter galaxy pairs in the spring sky.

An attractive eyepiece target. A 4-inch at moderate power shows two distinct elongated glows with a clear gap between them. An 8-inch at 150-200x reveals NGC 4490 as a clearly distorted bar-like streak with an irregular brightness pattern, while NGC 4485 sits to the north as a smaller, more concentrated patch. A 12-inch begins to bring out the brighter HII knots in NGC 4490's disk and hints of the connecting tidal bridge. Star-hop from Beta Canum Venaticorum (Chara) about 3 degrees south. Best observed February through June.

Discovered by William Herschel on 14 January 1788. The pair has been studied repeatedly with HI-line radio surveys, which revealed the diffuse intergalactic gas envelope and tracked the geometry of the encounter. NGC 4490 hosted SN 1982F, a Type II supernova that briefly outshone its nucleus.