What is Einstein's Cross?
{{about|the quasar|the astrophysics concept|gravitational lens}} [[File:Einstein cross.jpg|thumb|right|250px|Einstein's Cross]] '''Einstein's Cross''' <ref>''Q2237+030'' or ''QSO 2237+0305''</ref> is an image of a [[quasar]] which is 8,000,000,000 [[light years]] (ly) or 2,500,000,000 [[parsecs]] (pc) away. The quasar sits directly behind ZW 2237+030, '''Huchra's lens''', the lensing galaxy. Four images of the same distant quasar appear around this foreground galaxy due to strong [[gravitational lensing]]. According to its [[redshift]], the quasar is about 8 [[billion]] [[light year]]s from Earth, while the lensing galaxy is only 400 million light years away.<ref>{{cite web | last = NASA and ESA | date = 1990 | url = http://hubblesite.org/newscenter/newsdesk/archive/releases/1990/20/image/a | title = The gravitational lens G2237 + 0305 | work = HubbleSite | accessdate = July 25, 2006 }}</ref> Amateur astronomers are able to see some of the cross using telescopes but it requires extremely dark skies and telescope mirrors with diameters of 18 inches or greater.<ref>The Einstein Cross can be seen in [[Pegasus (constellation)|Pegasus]] at 22h40m30.3s +3d21m31s. </ref><ref>{{cite web|url = http://observing.skyhound.com/archives/sep/Q2237+0305A.html|title = Focus on Einstein's Cross|last = Crinklaw|first = Greg|accessdate = 2013-06-29}}</ref> == References == {{reflist}} [[Category:Quasars]]