NGC 4485/90, Cocoon Galaxy

Object Description

NGC 4485/90
NGC 4485/90: NGC 4485 (top) and NGC 4490 (bottom). Section of the Two Micron All Sky Survey (2MASS) [147]

This pair of galaxies was discovered by William Herschel on January 14, 1788. As for most of his discoveries he was using his 18.7 inch reflecting telescope with 20 feet focal length. He cataloged his discovery as I 197 (NGC 4485) and I 198 (NGC 4490). In his «Catalogue of a second Thousand of new Nebula and Clusters of Stars» he described it as: «Two. The southern very bright, very large, irregular extended. The northern bright, pretty small, irregular faint. Distance 1' 1/2.» [464]

The galaxy NGC 4490 is known as the Cocoon. In fact, their shape is reminiscent of a pupae of a caterpillar or even a nascent butterfly. The brighter and larger galaxy NGC 4490 is accompanied by the smaller galaxy NGC 4485 in the immediate vicinity. It appears that the two galaxies are gravitationally affecting each other. [192] Measured distances vary from 6.9 Mpc to 11 Mpc. [145]

«Catalogue of Principal Galaxies (PGC)», Paturel et al. 1989 [144]
NameRA [hms]Dec [dms]mTypeDim [']Btot [mag]HRV [km/s]PA [°]
NGC 448512 30 31.6+41 42 01IB M2.4 x 1.812.349615
NGC 449012 30 36.6+41 38 22SB M6.4 x 3.210.2579125

Finder Chart

The galaxy pair is located in the constellation Canes Venatici and is very easy to find: Extend the connecting line from the two stars Cor Caroli (α Canum Venaticorum, 2.9 mag) to the 4.2 mag star Chara (β Canum Venaticorum) by about 40 arc minutes . The two galaxies should already be visible in the eyepiece.

Chart NGC 4490
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

Visual Observation

NGC 4485 + NGC 4490
NGC 4485 + NGC 4490: Pencil drawing; 14" PWO-Dobson f/4.6, TV-Radian 8 mm, 200x, 0.3°, D: 6.7, air: quiet; Blattisiten 1300m; © 6. 6. 2003, 01:15 Eduard von Bergen

350 mm aperture: A slight bend can be seen on NGC 4490 and further it has a bright elongated core. To the southeast, they are joined by a mag 14.2 star just at the galaxy's end. Almost inconspicuously, the star binds to NGC 4490. The galaxy NGC 4485 is much smaller and slightly fainter than its sister. It also has a noticeably brighter galactic core. [192]

14" PWO-Dobson, F:4.6 / TV-Radian 8mm, 200x, 0.3°
Eduard von Bergen

References

144Catalogue of Principal Galaxies (PGC); Paturel G., Fouque P., Bottinelli L., Gouguenheim L.; Astron. Astrophys. Suppl. Ser. 80, 299 (1989); cdsarc.unistra.fr/viz-bin/cat/VII/119 (2021-02-18)
145SIMBAD astronomical database; simbad.u-strasbg.fr/simbad
147Aladin Lite; aladin.u-strasbg.fr/AladinLite (2020-12-23)
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
192Deep-Sky Guide; fernrohr.ch/1d_deep-sky-guide.html (2020-12-25)
464«Catalogue of a second thousand of new nebulae and clusters of stars; with a few introductory remarks on the construction of the heavens» William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1789; DOI:10.1098/rstl.1789.0021