Talk:Angular diameter
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Should this page be categorized in Observational Astronomy?
[edit] Sun diameter inaccurate?
The angular diameter of the Sun is quoted as 30'
Elsewhere, the entry for the Sun gives mean distance and diameter figures which would correspond to about 32'
This discrepancy should be resolved.
86.141.38.201 13:02, 18 April 2007 (UTC)Peter
- You are correct - I shall adjust. Jim77742 11:43, 9 September 2007 (UTC)
Me have question. I did the simple trig and I get theta = 2arctan(d/2D). Obviously, due to small angle approximation, it's close enough, but... I haven't found much (conclusive) evidence in either direction, however. Anyone mind checking? Jeff 01:26, 3 July 2007 (UTC)
- You are correct - I shall adjust. Jim77742 11:43, 9 September 2007 (UTC)
Sorry chaps, the correct formula for the angular diameter of a sphere is theta = 2arcsin(d/2D) and not the one currently shown. River6rat 13:49, 2 October 2007 (UTC)
[edit] This article needs improving
Check this:
* Betelgeuse: 0.049″ – 0.060″ * Alpha Centauri A: ca. 0.007″ * Sirius: ca. 0.007″
What's "ca" mean?
And these paragraphs:
- This meaning the angular diameter of the Sun is ca. 250,000 that of Sirius (it has twice the diameter and the distance is 500,000 times as much; the Sun is 10,000,000,000 times as bright, corresponding to an angular diameter ratio of 100,000, so Sirius is roughly 6 times as bright per unit solid angle).
- The angular diameter of the Sun is also ca. 250,000 that of Alpha Centauri A (it has the same diameter and the distance is 250,000 times as much; the Sun is 40,000,000,000 times as bright, corresponding to an angular diameter ratio of 200,000, so Alpha Centauri A is a little brighter per unit solid angle).
- The angular diameter of the Sun is about the same as that of the Moon (the diameter is 400 times as large and the distance also; the Sun is 200,000-500,000 times as bright as the full Moon (figures vary), corresponding to an angular diameter ratio of 450-700, so a celestial body with a diameter of 2.5-4" and the same brightness per unit solid angle would have the same brightness as the full Moon).
How is this really relevant? I find it confusing and not very useful. I would like to remove them. But I'd prefer comment before I do.Jim77742 11:43, 9 September 2007 (UTC)
[edit] Angular Diameter of planets from Earth
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)
- 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)
