3C 20

{{Short description|Radio galaxy in the constellation Cassiopeia}}

{{Infobox galaxy

| name = 3C 20

| image = 3C_20_HST_n90j04010_mos.jpg

| epoch = J2000

| ra = {{RA|00|43|08.84}}{{cite web

| title=NASA/IPAC Extragalactic Database

| work=Results for QSO B1637+826

| url=http://nedwww.ipac.caltech.edu/

| access-date=2006-10-26 }}

| dec = {{DEC|+52|03|33.8}}

| constellation name = Cassiopeia

| z = 0.174

| type = E

| dist_ly = ~ 700 Mpc

| appmag_v = 19[http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=QSO+B0040%2B517&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id Simbad]

| size_v = 76.8 × 76.8 arcsec²[http://www.jb.man.ac.uk/atlas/object/3C20.html www.jb.man.ac.uk/atlas/] (radiogalaxy)

| notes =

| names = DA 22, LEDA 2817481, 3C 20

}}

3C 20 is a radio galaxy{{cite journal |last1=Hiltner |first1=P. R. |last2=Meisenheimer |first2=K. |last3=Roeser |first3=H. J. |last4=Laing |first4=R. A. |last5=Perley |first5=R. A. |title=Hot SPOT 3C20 west: an optical synchrotron source |journal=Astronomy and Astrophysics |volume=286 |pages=25–36 |year=1994 |bibcode=1994A&A...286...25H}} located in the constellation Cassiopeia. It is one of largest known galaxies with a diameter of {{convert|850,000|ly|kpc|abbr=on|lk=on}}.{{efn|name=size|Calculated from apparent size and distance:$700\; Mpc*sin(76.8\; arcsec)\; =\; 850,000\; ly$}} The galaxy features a prominent double hotspot in its eastern lobe. An unusually low fraction of the flux lies within the radio core, which is suggested to be caused by a combination of factors, including jet orientation, synchrotron self-absorption and aging, as well as interactions with surrounding gas and dust.{{Cite journal |last1=Hardcastle |first1=M. J. |last2=Alexander |first2=P. |last3=Pooley |first3=G. G. |last4=Riley |first4=J. M. |date=1997-07-11 |title=High-resolution observations at 3.6 cm of seventeen FR II radio galaxies with 0.15 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=288 |issue=4 |pages=859–890 |doi=10.1093/mnras/288.4.859 |doi-access=free |issn=0035-8711}}

File:3C_20_Radio_Image.jpg