Talk:Square degree

Two dimensional?
I fear this article is not clear enough... Since degrees are two-dimensional (the angle formed by the intersection of oblique unidimensional objects in two dimensions)
 * I agree with that. The article contains no clear definition of a square degree, only a conversion factor between steradian and square degree. Is someone able to give a definition of a square degree without knowledge of steradians? Michel Arts (talk) 22:22, 13 October 2011 (UTC)

Formula!
This page has to have a formula. It comes so close, 1/2° is 0.2 sq.deg, but we don't know how to get from one to the other. McKay 05:20, 12 October 2006 (UTC)


 * The Moon and the Sun are circles, so area A = πr².


 * The diameter d ≈ ½°, the radius r = d/2, so A ≈ π × (½/2)²≈ 0.196 ≈ 0.2 sq.deg.


 * HTH. -- ALoan (Talk) 09:51, 12 October 2006 (UTC)

When d is small this will be reasonably accurate. In general, though, the solid angle Ω subtended by a circle with a "radius" of angle r (= d/2) on the surface of a sphere will be Ω = 2π × (1 - cos r). (Note that in the limit r -> 0, this will converge to the expected result of πr², easily checked by substituting the Taylor series for cosine of r.) This gives results in steradians; for Ω in square degrees, substitute 2π by 2π × (180/π)² deg² = (64800/π) deg² and, of course, convert degrees to radians in the argument to the cosine.

For instance, a circle with a radius of 1 degree on the surface of a sphere will not cover a solid angle of exactly π deg², but instead something slightly smaller. Contrariwise, a circle covering a solid angle of π deg² will not subtend a radius of 1°, but instead something slightly larger (about 1.00001269°).

65.211.242.6 (talk) 15:48, 4 May 2011 (UTC) (Kevin B. McCarty)

Symbol
Various symbols for "square degree" are claimed in different sources, including at least: Anybody know which ones are really in common use and/or listed in reputable reference works? This Wikipedia article used to list symbols 1–3 but after this edit only mentions the second one (deg²). Is there a particular reason not to mention the others? --Jmk (talk) 10:26, 5 May 2009 (UTC)
 * 1) sq.deg.
 * 2) deg²
 * 3) □°
 * 4) (°)²
 * 5) sq °


 * Well, this discussion has been underwhelming. I added symbols 1 and 4 to the article. --Jmk (talk) 12:20, 9 September 2009 (UTC)


 * Over the years I have seen all variants but variant 3) being used in books, including historical literature. --Matthiaspaul (talk) 01:43, 27 October 2015 (UTC)

external link
The external link http://www.badastronomy.com/bitesize/bigsky.html has been added and removed from this page three times. The reason given for its removal was WP:EL, but that does not seem adequate. Is there a more specific reason why it should not be listed here? --Lasunncty (talk) 10:20, 18 August 2009 (UTC)
 * Probably what was meant was WP:ELNO Point 11. Links to blogs are normally to be avoided. Given that the author, Phil Plait has his own article, you might make a case that he's a "recognized authority". The contributors at the Reliable Sources Noticeboard at WP:RS/N might have an opinion on the matter. AlmostReadytoFly (talk) 13:31, 9 September 2009 (UTC)

When, who and what?
When was the square degree devised, by whom and for what purpose? Are there practical examples outside astronomy and geography, perhaps in an engineering discipline? 92.13.59.35 (talk) 11:06, 1 May 2018 (UTC)