NGC 4490 — SBcd in Canes Venatici

About NGC 4490

NGC 4490, the Cocoon Galaxy, is interacting with its small neighbour NGC 4485. The encounter has triggered a burst of star formation, and a long trail of gas surrounds the pair. Its shape gives it its nickname.

What you are looking at

NGC 4490 is a late-type spiral: a small central bulge and open, loosely wound arms full of young stars and star-forming gas. A bar of stars runs straight across its centre, as one does across the centre of the Milky Way. Its disc is turned almost exactly side-on to us: the galaxy appears as a narrow blade of light, and its dust as a dark seam running along it. From edge to edge its visible disc spans about 55,000 light-years (taking its redshift distance, which for a galaxy this near is approximate), about half the width of the Milky Way.

What astronomers have recorded

SIMBAD, the reference database astronomers use, classes it as a member of a group of galaxies. Halton Arp included it in his 1966 Atlas of Peculiar Galaxies as Arp 269, a list of galaxies with unusual, disturbed shapes. Boris Vorontsov-Velyaminov listed it as VV 30 in his catalogue of interacting galaxies. Two supernovae have been recorded in it, the first in 1982; the most recent include SN 1982F, SN 2008ax. It is cited in 627 scientific papers indexed by SIMBAD, and recorded there under 48 different catalogue designations.

When this light set out

What a telescope records of NGC 4490 is light that left it about 28 million years ago; on Earth, Antarctica had begun to freeze. The galaxy is moving away from us at about 587 km/s (1.3 million mph), carried by the expansion of the universe. For a galaxy this close, its own motion through space is a large share of that speed, so the distance worked out from it is approximate; distances measured from individual stars in it can differ.

Finding it in the sky

In the sky, NGC 4490 sits within the constellation Canes Venatici. It is best placed on spring evenings: around 9:30 pm in May it stands about 88° high in the north, close to overhead, seen from the middle of the United States.

Its neighbours

At almost the same distance from us, and so its neighbours in space as well as on the sky: NGC 4485 (4′ away on the sky, at least 30,000 light-years from it); UGC 7690 (1.1° away on the sky, at least 550,000 light-years from it); UGC 7608 (1.6° away on the sky, at least 800,000 light-years from it); UGC 7774 (2.0° away on the sky, at least 970,000 light-years from it), and 3 more.

By apparent size it is number 53 of the 12,657 galaxies on the Galaxy Origins register.