:NGC 646
{{Short description|Galaxy in the constellation Hydrus}}
{{Infobox galaxy
| name = NGC 646
| image = Arp-Madore 135-650.png
| appmag_b = 15.65
| sbrightness = 22.53 mag/arcsec2
| epoch = J2000
|constellation name=Hydrus
|dist_ly=392 Mly
}}
NGC 646 is a large barred spiral galaxy located in the constellation Hydrus.{{Cite web |title=NGC 646 NED02 - Elliptical/Spiral Galaxy in Hydrus {{!}} TheSkyLive.com |url=https://theskylive.com/sky/deepsky/ngc646-ned02-object |access-date=2024-04-15 |website=theskylive.com}} Its speed relative to the cosmic microwave background is 8,145 ± 19 km/s, which corresponds to a Hubble distance of 120.1 ± 8.4 Mpc (~392 million ly). NGC 646 was discovered by British astronomer John Herschel in 1834.{{Cite web |title=New General Catalog Objects: NGC 600 - 649 |url=https://cseligman.com/text/atlas/ngc6.htm#646 |access-date=2024-04-18 |website=cseligman.com}} It forms an interacting galaxy pair.{{Cite journal |last1=Danziger |first1=I. J. |last2=Schuster |first2=H. -E. |date=1974-08-01 |title=The interacting galaxy system NGC 646. |url=https://ui.adsabs.harvard.edu/abs/1974A&A....34..301D |journal=Astronomy and Astrophysics |volume=34 |pages=301–303 |bibcode=1974A&A....34..301D |issn=0004-6361}}
Luminosity
The luminosity class of NGC 646 is III.{{Cite web |title=Your NED Search Results |url=https://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Obj_id&objid=4491&objname=1&img_stamp=YES&hconst=73.0&omegam=0.27&omegav=0.73&corr_z=1 |access-date=2024-04-18 |website=ned.ipac.caltech.edu}} It has surface brightness equal to 14.69 mag/am2.{{Cite web |url=http://astrovalleyfield.ca/AstronomieCompl/NGC%20et%20autres/WolfgangS/N0600_exc_web.htm |access-date=2024-05-03 |website=astrovalleyfield.ca}} NGC 646 is a low surface brightness galaxy (LSB). LSB galaxies are diffuse (D) galaxies with a surface brightness less than one magnitude lower than that of the ambient night sky.
Distance
The Hubble distance of PGC 6014, the galaxy to the east of NGC 646, is 106.4 ± 7.5 Mpc (~347 million ly).{{Cite web |title=Your NED Search Results |url=https://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Obj_id&objid=219651&objname=6&img_stamp=YES&hconst=73.0&omegam=0.27&omegav=0.73&corr_z=1 |access-date=2024-04-18 |website=ned.ipac.caltech.edu}} A distance of approximately 45 million light years therefore separates these two galaxies which appear to be neighbors in the image. Their gravitational interaction, if there is any interaction, should therefore be of short duration.{{Cite web |title=New General Catalog Objects: NGC 600 - 649 |url=https://cseligman.com/text/atlas/ngc6.htm#646 |access-date=2024-04-18 |website=cseligman.com}}
See also
External links
- [https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=NGC+646&submit=SIMBAD+search NGC 646] at SIMBAD