Talk:Geometric albedo

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I have removed the following text from the article. It seems that it is not strictly true:

This concept arises because the reflectivity of all surfaces, natural or man-made, depends on the angle of incidence as well as the azimuth of the incoming light beam (more generally electromagnetic radiation).

Note that, strictly speaking, the geometric albedo is only defined

• for objects that are flat, at least on the spatial scale at which measurements are acquired (the angle of incidence is undefined or quite variable for non-flat objects), and
• for direct beam illumination (by definition diffuse illumination impinges on a surface from a variety of incidence angles).

A) The concept arises primarily because it is useful, I would say.

B) It's clearly defined quite well for non-flat objects since thet's where it's actually used Deuar 23:47, 30 June 2006 (UTC)[reply]

In principle the problem for a non-flat object is that you don't know where exactly (at which distance from the light source) to place the flat disk; and strictly speaking maybe it shouldn't be flat, but cut out of a sphere centered at the light source. The article now states that the disk should have the "same cross-section"; if you mean - in the case of a perfect ball or sphere - a disk with the same diameter, then the disk will look smaller if it is placed at a distance so that the centers of the ball and the disk coincide. However, the differences in the albedo caused by this would be negligible for most astronomical purposes. Icek (talk) 21:41, 25 March 2011 (UTC)[reply]

The geometric albedo value for Venus should be around 0.65. see <url>http://ssd.jpl.nasa.gov/?planet_phys_par#B</url>[[User::Sigi_E|Sigi_E]] 16:18, 9 November 2009 (UTC+1) —Preceding unsigned comment added by Sigi E (talk • contribs)

Geometric albedo value for Venus changed from 0.84 to 0.65. [User::Sigi_E|Sigi_E]] 16:, 9 November 2009 (UTC+1) 25

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