Talk:Angular diameter

message: Should this page be categorized in Observational Astronomy?
:Not necessarily. Angular diameter is a geometric concept that applies to perspective, and not solely to astronomy  — Preceding unsigned comment added by Octachoron (talk • contribs) 02:55, 8 June 2014 (UTC)
thread_title: Categorization

message: Should this be appended to say that it is the angular diameter as viewed from Earth when the various bodies are closest to the Earth in their orbits? Otherwise this can be minorly misleading. Jacotto (talk) 02:39, 4 April 2008 (UTC)
replies: text: It is not for when objects are closest to Earth.  Look at Venus (closest) and Jupiter (largest) for two great examples.  They are given as a range.  Planets that are very far from the Earth simply do not vary enough to bother with a range.  Only a professional telescope under the best of circumstances will resolve Ceres or Pluto as a small sphere. -- Kheider (talk) 03:27, 4 April 2008 (UTC)
replies: text: Thanks for the clarification. Jacotto (talk) 16:27, 4 April 2008 (UTC)
thread_title: Angular Diameter of planets from Earth

message: When formulas are used, should there either be explanations (or examples) of each mathematical term?  Or else, links to Wiki math pages that explain them?  Not all of us are math wizards -- so terms such as "arctan" and "arcsin" are lost on us.
:Thanks  —Preceding unsigned comment added by 75.45.95.166 (talk) 15:51, 2 August 2008 (UTC)
thread_title: Formulas

message: The Sun appears to be wider when close to the horizon, please explain why and how much.  — Preceding unsigned comment added by 201.141.5.237 (talk) 06:09, 26 January 2014 (UTC)
replies: text: No, the Sun isn't wider when it's closer to the horizon. It's flattened top to bottom by refraction. Refraction is greater closer to the horizon so the lower limb of the Sun is lifted more than the upper limb causing that flattening. There is also a perceptual illusion when the Sun or especially the Moon is close to the horizon, known as the "Moon Illusion", which makes astronomical objects look larger near the horizon, but this is entirely in our heads. There is no magnification by the atmosphere. In fact, the Sun and Moon are actually slightly smaller (when measured objectively) when they are on the horizon, due to both the flattening from refraction and the slightly greater distance. 70.192.19.6 (talk) 18:51, 6 April 2014 (UTC)
thread_title: Atmosphere lens effect

message: So the apparent size of an object is related arccotangentially to the distance from the object?  —Preceding unsigned comment added by 67.232.193.190 (talk) 02:28, 7 December 2008 (UTC)
thread_title: Apparent Size

message: The caption for Figure 2 entitled "angular diameter" is more than a little strange.  Comparison to a "football" is meaningless without giving the distance to the football.  Also, Pluto's orbital radius averages about 40 AU.  But a tennis ball is NOT 40 times smaller in diameter than a football.  It doesn't matter whether "football" refers to a soccer ball or a "pigskin" viewed from the end.  The figure is helpful enough without the nonsensical statements in the caption.
— Preceding unsigned comment added by 140.208.1.244 (talk • contribs) 20:34, 9 March 2009 (UTC)
thread_title: Comments about Figure 2

message: The caption of the second diagram reads as follows:
Angular diameter : The sun appears the size of a football when seen from Earth. But when it is seen from Pluto (The dwarf planet - plutoid) its size will be like a tennis ball.
This is meaningless unless some indication is given of the distance at which the ball is held.  I haven't checked—it's raining today, and I don't have a football anyway—but I'm pretty sure that the angular diameter of a football held at arm's length (whose arm?) is larger than that of the sun.
DES (talk) 14:16, 4 August 2009 (UTC)
thread_title:  Football and tennis ball 

message: These three articles overlap greatly. Surely one robust article is better than bits across three articles? Casliber (talk · contribs) 20:51, 13 August 2010 (UTC)
replies: text: Yes. JRSpriggs (talk) 00:11, 14 August 2010 (UTC)
thread_title:  Merge discussion 

message: #Casliber (talk · contribs) 20:51, 13 August 2010 (UTC)
thread_title: Support

message: # While the other two may be be roughly the same, Angular diameter distance is different (albeit related). Unlike the others, it has to do with cosmology. JRSpriggs (talk) 23:37, 13 August 2010 (UTC)
thread_title: Oppose

message: *I suppose I shouldn't have made this so black and white - I guess you support the merging of  Angular distance and Angular diameter with each other then in the interests of rationalising? Casliber (talk · contribs) 23:40, 13 August 2010 (UTC)
replies: text: Yes. JRSpriggs (talk) 00:11, 14 August 2010 (UTC)
thread_title: Discussion

message: "For a spherical object whose actual diameter equals d_\mbox{act}, and where D is the distance to the centre of the sphere, the angular diameter can be found by the formula:
\delta =  \arcsin \left( \tfrac{d_\mbox{act}}{D}\, \right)" — Really? No, \delta = 2 \arcsin \left( \tfrac{d_\mbox{act}}{2D}\, \right); just draw the right triangle. Boris Tsirelson (talk) 18:53, 5 September 2014 (UTC)
thread_title:  Wrong formula 

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thread_title:  External links modified 

message: Below the amount given to be the "Maximum resolvable diameter by the human eye", are Mars and several stars which are visible to the naked eye.
If we can't see an apparent diameter smaller than that maximum amount, then how can we see Mars and Alnitak for example? Aminabzz (talk) 21:55, 18 May 2023 (UTC)
replies: text: We can detect planets and stars because they send nonzero photons to our eye, all nearly parallel so they hit a small patch of receptors, and thus have contrast with the surrounding darkness.  But we cannot resolve them, that is, we cannot distinguish any two points on Mars, and thus cannot say anything about its shape; it's all the same smudge of light. —Tamfang (talk) 04:57, 4 June 2023 (UTC)
replies: text: Can you distinguish any two points on Venus then?! Aminabzz (talk) 20:28, 12 August 2023 (UTC)
thread_title:  Maximum resolvable diameter by the human eye