Talk:Hoag's Object

Object size
I've looked at this object on the DSS2 red plates, and it is much closer to one minute of arc in size. I suspect the size given here of 0.25' is of the central bright disk, and not the entire object. This needs revising. Fehrgo (talk) 06:13, 15 March 2008 (UTC)

OK, Hoag quotes the radius as 17".

"This object, which appears to be a perfectly symmetrical planetary nebula, was discovered on a 75-minute Jewett Schmidt plate. A perfect halo, 17" in radius, surrounds a difuse central image." The Astronomical Journal, No 1186

Fehrgo (talk) 06:22, 15 March 2008 (UTC)
 * And here I thought it meant "inches", and edited it out, and had to revert myself for stupidity. I included a "(minutes of arc)" thing for less-astronomically fluent people such as myself. Did the radius versus diameter thing get corrected yet? Huw Powell (talk) 02:10, 9 June 2008 (UTC)

Core brightness?
Looking at this object naively, it is tempting to think that someone in the rim stars would see a central "sun" in the sky, but it isn't so. A back of the envelope calculation seems to indicate that IF most of the object's brightness is in the center (not clear to me, and I haven't checked multiple/UV frequencies) then the center should be about as bright as perhaps Jupiter, Mars, or Mercury from the inner rim, but more diffuse. It would only be as bright as the Sun from a hypothetical 1.4 light years' distance as a point source, which is impossible due to the size of the center. I think discussion of this type would be instructive, but it's not legitimate to include it from my lips. Could someone dig up a source, or perhaps a faculty member might find it worth working out the math on a web site that can be used for citation? Wnt (talk) 17:57, 3 September 2008 (UTC)

Ring galaxy in two thirty ?
Ring galaxies are very rare. The most discussed theory how they were formed is a collision which was very long ago. If really two or three ring galaxies are congregated at the same place (and have similar z) probably it should be considered a collision theory which produces  more that one ring galaxy in a natural way. PANAMATIK (talk) 00:29, 7 January 2010 (UTC)


 * The small ring galaxy is much farther away. It's just one of those fascinating coincidences that it just happens to be in the right place for us to see it within the Hoag Object's ring. --Dmh (talk) 21:21, 22 August 2010 (UTC)

Size comparison
The claim is repeated here from Livescience.com that the object with a diameter of approximately 121,000 ly is "slightly larger than the Milky Way". It is my opinion that no one who doesn't know that the Milky Way's diameter is between 150,000 and 200,000 ly ought to be contributing to astronomical articles. OTOH, I'm no expert and it is possible that the size estimates are based on different metrics. For instance the Hoag Object's diameter is almost certainly based on visual observation of captured/recorded images while I believe our own galaxy's diameter is inferred from less direct approaches (since we're inside it, we can't "see" its "edges"...). I am removing this part of the sentence. Unless someone can verify that independently, it contradicts more established facts. And if someone can verify that 121 kly is larger than 150+ kly then that ought to be mentioned to reconcile a seeming contradiction.40.142.191.32 (talk) 20:23, 3 December 2019 (UTC)
 * Seems like the size of the Milky Way is not widely agreed upon? I can see sources including NASA as recently as May 2018 listing the diameter as 100,000 light-years, which would in fact be a bit smaller than 121,000. A bit confusing, since the discoveries from 2015 appear to me as rather conclusive. I'm not an expert either though.&#32;-- Fyrael (talk) 21:27, 3 December 2019 (UTC)

Star count?
The lead section states the star count as 8 billion (8e9), but all the other stats and comparisons to MW are in the 2nd section. (1) This is bad style: The star count should not be an isolated "factino". (2) Do we really believe that only 1% of its mass is in stars? Can we confirm that? (Compare MW, where roughly 50% is in stars.) I suspect we would be barely able to photograph a galaxy of only 8e9 stars at this distance, with the separate ring & core structure that we indeed see. Jmacwiki (talk) 16:28, 27 October 2023 (UTC)