Type of Object:  Cas A is the strongest radio source outside of our solar system.  It is the remnant of a supernova which is thought to have occurred in the year 1667.  However, no records from that time indicate an exploding star. This is puzzling because the radio and x-ray intensities are very high suggesting the supernova was extremely energetic. So, why was the event not noted during the 1600’s?

Distance: 9100 light years (= 8.6 x 10¹⁶ km = 5.4 x 10¹⁶ miles)
Size: About 8.4 light years across (= 8.0 x 10¹³ km = 3.6 x 10¹³ miles)
Coordinates (Epoch J2000):
         Right Ascension:        23 23 24.0
         Declination:                +58 48 54.0

Other Names: 3C 461, W 81, SN 1680, CTB 110

Radio Brightness at 1420 MHz (21 cm): 2240 Jy

Some Links
http://www.seds.org/~spider/spider/Vars/casA.html
http://chandra.harvard.edu/press/casfact.html

Location on the sky: The supernova remnant Cas A is located about twice the distance from the leg of the constellation Cassiopea as shown in the figure to the right. Since Cassiopea is a northern circumpolar constellation, Cas A can possibly be seen all year round from northern latitudes.

Images shown below, at different wavelengths, cover a 0.5 degree x 0.5 degree area of the sky centered on the nebula.  The images are taken from  the SKYVIEW Virtual Observatory maintained under NASA ADP Grant NAS5-32068 with P.I. Thomas A. McGlynn under the auspices of the High Energy Astrophysics Science  Archive Research Center (HEASARC) at the GSFC Laboratory for High Energy Astrophysics. SKYVIEW contains catalogs and surveys from x-ray to radio observations. The site is located at http://skyview.gsfc.nasa.gov/

Visible image from the digitized Palomar Sky Survey E plates.  Shows the stellar and optical nebulosity. Far-Infrared Image at 100 microns taken by the Infrared Astronomical Satellite (IRAS) Survey. Shows the dust component of the nebulosity. Image taken at the radio emission of neutral hydrogen at 1420 MHz by the NRAO VLA Sky Survey.  Shows the gas component of the remnant. Image taken at the radio emission frequency of 4850 MHz.  Image shows the gas component and looks very similar to the 1420 MHz image.  Image is from a Green Bank survey from 0° to +75° declination).