Cas A SNR home


Cassiopeia A

Visual observation of the youngest supernova remnant in our Milky Way


December 2009 

Cassiopeia A (wiki) is a very recent supernova remnant (SNR) and probably the youngest in our Milky Way. The supernova light arrived here only around 1680 and was probably seen only by Flamsteed.

This SNR, which is shown to the left as a DSS composite, is again an object that I had tried to observe one or two years ago without success and that proved relatively easy some other night (for whatever reason). Encouraged by positive reports on the AmAstro Yahoo group, I wanted to tackle this SNR again.

Without filter, at 200 and 350x, I suspected an elongated glow at the correct position, which contains, however, also several tiny stars. Three stars form an almost equilateral triangle and could be held almost steadily. The crescent shaped nebulosity extended well beyond this triangle. With UHC filter, the SNR was easily identified as nebulosity (best at 200x) and clearly not caused by stars.  With OIII (Lumicon) the SNR could be seen as well, but not as prominent as with UHC. Here is a finder chart. According to the images, I had observed the central part of the northern shell (on the POSS image the small triangle is marked). The observed nebulosity was larger than this triangle.

Here is a narrow band image by Richard Crisp.

Deep image of Cas A by L. Rudnick, T. Delaney, J. Keohane & B. Koralesky (U. Minnesota) and T.A. Rector (NRAO)

Here is another image taken by the Hubble Space Telescope (more here). Nearby of the actual SNR, the observation of light echoes of the supernova proper were discovered. The spectroscopic characterization of the supernova light scattered by interstellar dust allowed  classification of the supernova as a Type II b SN with a time delay of more than 400 years (more here and here). 

DSS copyright notice and HST copyright notice