Talk:Cassiopeia A

3C 461
Someone has written about Cas A under the title 3C 461. I think all the info there should be moved here and that page made a redirect. (Although I REALLY doubt anyone will look up Cas A on Wiki using the Cambridge catalog number!) --Etacar11 23:53, 5 Jun 2005 (UTC)
 * Have done. The old article contained a few mistakes, which I'm working on correcting (its not the youngest for example). The whole SN/SNR template is a bit unwieldy though. Am thinking what to do about it. Some catagories don't make much sense. --Sillylizard 20:48, 8 Jun 2005 (UTC)


 * Cool. I'll take a look when I get a chance. --Etacar11 21:00, 8 Jun 2005 (UTC)

Also something is written under Sn 1680. I've added merge template. --xJaM 17:42, 23 March 2006 (UTC)
 * Yeah, I agree, merge it here. -- Etacar11   17:44, 23 March 2006 (UTC)


 * I did the merge. -- Etacar11   14:58, 25 March 2006 (UTC)

300 years old
It can't be. It may be 300 years since we saw the explosion but the star is 11,000 light-years from us. That means that the supernova must be at least 11,000 years old. If current observations appear to show the state of the supernova 300 years after the explosion, that implies that the explosion itself happened 11,300 years ago. We need to clarify this. -- Derek Ross | Talk 16:09, 30 May 2008 (UTC)
 * It's the convention in astronomy to say an event "happened" when we observe it from Earth. Distance can be very uncertain.  So it is indeed proper to say that the SN happened 300 years ago.  --  Etacar11   16:20, 30 May 2008 (UTC)


 * It may well be proper but for anyone unaware of that convention (ie the overwhelming majority of our readership) it is not at all clear. Hence my request for clarification. We are not writing this for astronomers, we are writing it for a general readership, so we need to avoid using technical conventions which are clear only to specialists. -- Derek Ross | Talk 02:56, 2 June 2008 (UTC)
 * Perhaps, but what we see from Earth is a 300 year old remnant. Not an 11,000+ year old one.  That should always stay clear. --  Etacar11   13:05, 2 June 2008 (UTC)
 * Not denying that but it should be possible to make both facts clear, not just the one. -- Derek Ross | Talk 05:15, 3 June 2008 (UTC)

SNR detectably cooling
Neutron Star Provides Direct Evidence for Bizarre Type of Nuclear Matter says how Chandra detected a cooling from 2.12 million K (in 2000) to 2.04 million K (in 2009), or 4%, in ~10 years, and suggests this could be due to neutrons pairing. Rod57 (talk) 01:41, 27 February 2011 (UTC)

Observability in visible light
Cassiopeia A is observable with a 9.25 inch amateur telescope with an O III optical filter according to this source. Please either add an inline citation to a reliable source or change it. Iwilsonp 22:51 (UTC) 5 Nov 2014

I easily recorded the remnant in November 2014 with a 102mm aperture refractor. Exposure was 4 hours using a UHC filter. David Ratledge

Where is Cas A?
Pretty frustrating that the article doesn't illustrate Cas A's location. I might suggest adding a simple diagram of the five stars that compose the Cassiopeia asterism plus a dot showing where Cas A is located. Because of the missing information, non-astronomers may even have trouble unraveling that "Cassiopeia A" is not one of the five stars in the asterism, but that it's floating elsewhere in the constellation-area. A picture would answer all the questions. 72.25.40.16 (talk) 07:09, 12 November 2014 (UTC) I would also add that the article states that Cas A is "3.4kp away within the Milky Way" This statement is ambiguous. Does this mean Cas A is 3.4kpc from the center of the Milky Way, or 3.5kpc from some point on the circumference of the Milky Way galaxy?

Proposed merger
There is an article 3 Cassiopeiae hidden away where most people will never find it. It is linked in a handful of articles, but none of the major astronomical navboxes or lists. The designation does not correspond to any known star, but has hypothetically been linked to two borderline-naked-eye stars and to the supernova progenitor of Cassiopeia A. The designation 3 Cassiopeiae is mentioned here and there is a section about potential observations of the supernova itself, which would be a good redirect target. Of the other two possible stars that Flamsteed may have observed, one has an article (AR Cas) that doesn't mention 3 Cas and the other (HD 220562) doesn't have an article and probably never will.

If not merged, it would be hard to expand the article much beyond its current size, but it could be linked more widely: for example, in the constellation navbox, which doesn't currently show 3 Cas; in List of stars in Cassiopeia, which also doesn't show 3 Cas; and in Table of stars with Flamsteed designations which shows 3 Cas but links it here. Lithopsian (talk) 14:32, 16 January 2023 (UTC)


 * Support the merge of 3 Cassiopeiae to Cassiopeia A as notability is not inherited and the information ties in nicely with Cassiopeia A. InterstellarGamer12321 ( talk &#124;  contribs ) 10:24, 3 April 2023 (UTC)
 * Support Not enough information here to justify a standalone article. –LaundryPizza03 ( d c̄ ) 07:24, 6 May 2023 (UTC)


 * Support. I don't understand the rationale for having a stand alone article about 3 Cassiopeiae. TowardsTheLight (talk) 13:39, 6 May 2023 (UTC)
 * I have performed this merge. Feel free to take a look that I placed it correctly; I'm not an astronomy expert just doing some cleanup. SomeoneDreaming (talk) 01:04, 9 July 2023 (UTC)