AMATEUR ASTRONOMY PAGES home                                3C461 - Cassiopeia A
Javier Gómez Laina                                                                                                        


Imaging 3C461 has an unusual feature: red signal is very, very stronger in SII band than in H-alpha's. I believe that it is one of a handful, if any, deep sky objects with that strange behaviour;  indeed, H-alpha regions in 3C461 are circunscribed to several little knots inside the nebula's ring and a very faint and difuse nebulosity zones surrounding 3C461.   These  H-alpha regions can be seen on the image as faint but pure green areas.  OIII and SII regions are in the remnant's main ring.
3C461, also known as Cassiopeia A (Cas A) is a supernova remnant in the Milky Way; it is believed that the supernova explosion was recorded visually on 1680 by John Flamsteed, the first British Astronomer Royal, who catalogued it as star "3 Cassiopeiae", although, because the position of "3 Cassiopeiae" does not precisely match that of 3C461, and because the expansion wave associated with the explosion has been worked backward to the year 1667 and not 1680, some historians feel that all Flamsteed may have done was incorrectly note the position of a star already known.  In that case, there would be no historical records of any sightings of the 3C461's progenitor supernova, probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth.
3C461 means that it is the 461st object in the Third Cambridge Catalogue of Radio Sources, it was one of the first objects discovered in early years of radio astronomy. One of the brightest radio source was in the region of the constellation Cassiopeia and so was named Cassiopeia A (then Cas A); indeed it is the brightest radio source in the sky beyond our solar system.  Despite so powerful radio emission, its optical appearance is extremely faint; in fact, whereas Cas A was among the first discrete radio sources to be found, in 1947, the optical component was first identified in 1950.

Object:             3c461    - supernova remnant -    
COMELLAS  telescope  (250 f/4.8 Newton). Lumicon coma corrector.
Camera:           Artemis ART4021
Filters:              Luminance: OIII ;   mapped color  SII : Ha : OIII
Exposures:       Ha:  17 x 900"     (  4:15 total) 
                         SII:  16 x 900"     (  4:00 total)
                         OIII: 55 x 900"     (13:45 total)
Resolution:       1.28"/pixel 
Date:                28 Oct - 1 Nov  2007
Guiding:            MX716 on Off-Axis Guider
Bias, Darks & Flat calibration
SDMask combining
Histogram, Curves and wavelets adjust
ACDNR noise reduction in PI

MaximDL, PixInSight, PhotoShop.