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  2. Steradian - Wikipedia

    en.wikipedia.org/wiki/Steradian

    A solid angle of one steradian subtends a cone aperture of approximately 1.144 radians or 65.54 degrees. In the SI, solid angle is considered to be a dimensionless quantity, the ratio of the area projected onto a surrounding sphere and the square of the sphere's radius. This is the number of square radians in the solid angle.

  3. Solid angle - Wikipedia

    en.wikipedia.org/wiki/Solid_angle

    In the International System of Units (SI), a solid angle is expressed in a dimensionless unit called a steradian (symbol: sr), which is equal to one square radian, sr = rad 2. One steradian corresponds to one unit of area (of any shape) on the unit sphere surrounding the apex, so an object that blocks all rays from the apex would cover a number ...

  4. Square degree - Wikipedia

    en.wikipedia.org/wiki/Square_degree

    The full moon covers only about 0.2 deg 2 of the sky when viewed from the surface of the Earth. The Moon is only a half degree across (i.e. a circular diameter of roughly 0.5°), so the moon's disk covers a circular area of: π (⁠ 0.5° / 2 ⁠) 2, or 0.2 square degrees.

  5. Unit sphere - Wikipedia

    en.wikipedia.org/wiki/Unit_sphere

    The unit sphere is often used as a model for spherical geometry because it has constant sectional curvature of 1, which simplifies calculations. In trigonometry , circular arc length on the unit circle is called radians and used for measuring angular distance ; in spherical trigonometry surface area on the unit sphere is called steradians and ...

  6. Pseudomathematics - Wikipedia

    en.wikipedia.org/wiki/Pseudomathematics

    Common examples of this include the following constructions in Euclidean geometry—using only a compass and straightedge: Squaring the circle: Given any circle drawing a square having the same area. Doubling the cube: Given any cube drawing a cube with twice its volume.

  7. Geometrical-optical illusions - Wikipedia

    en.wikipedia.org/wiki/Geometrical-optical_illusions

    Application of differential geometry has so far not been notably successful Archived 2012-03-25 at the Wayback Machine; the variety and complexity of the phenomena, significant differences between individuals and dependence on context, previous experience and instruction set a high bar for satisfying formulations.

  8. Gradian - Wikipedia

    en.wikipedia.org/wiki/Gradian

    In trigonometry, the gradian – also known as the gon (from Ancient Greek γωνία (gōnía) 'angle'), grad, or grade [1] – is a unit of measurement of an angle, defined as one-hundredth of the right angle; in other words, 100 gradians is equal to 90 degrees.

  9. Geon (psychology) - Wikipedia

    en.wikipedia.org/wiki/Geon_(psychology)

    Two cases of two interrelated geons, What does the reader imagine in each case? There are 4 essential properties of geons: View-invariance: Each geon can be distinguished from the others from almost any viewpoints except for “accidents” at highly restricted angles in which one geon projects an image that could be a different geon, as, for example, when an end-on view of a cylinder can be a ...