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  2. Empirical evidence for the spherical shape of Earth - Wikipedia

    en.wikipedia.org/wiki/Empirical_evidence_for_the...

    Refraction can give the impression that Earth's surface is flat, curved more convexly than it is, or even that it is concave (this is what happened in various trials of the Bedford Level experiment). The phenomenon of variable atmospheric bending can be seen when distant objects appear to be broken into pieces or even turned upside down.

  3. Bedford Level experiment - Wikipedia

    en.wikipedia.org/wiki/Bedford_Level_experiment

    The Old Bedford River, photographed from the bridge at Welney, Norfolk (2008); the camera is looking downstream, south-west of the bridge. The Bedford Level experiment was a series of observations carried out along a 6-mile (10 km) length of the Old Bedford River on the Bedford Level of the Cambridgeshire Fens in the United Kingdom during the 19th and early 20th centuries to deny the curvature ...

  4. Atmospheric refraction - Wikipedia

    en.wikipedia.org/wiki/Atmospheric_refraction

    Diagram showing displacement of the Sun's image at sunrise and sunset Comparison of inferior and superior mirages due to differing air refractive indices, n. Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. [1]

  5. Horizon - Wikipedia

    en.wikipedia.org/wiki/Horizon

    where h is the observer's height above the Earth, μ is the index of refraction of air at the observer's height, and μ 0 is the index of refraction of air at Earth's surface. The refraction must be found by integration of = ⁡, where is the angle between the ray and a line through the center of the Earth.

  6. Levelling refraction - Wikipedia

    en.wikipedia.org/wiki/Levelling_refraction

    Levelling refraction refers to the systematic refraction effect distorting the results of line levelling over the Earth's surface. In line levelling, short segments of a line are levelled by taking readings through a level from two staffs, one fore and one behind. By chaining together the height differences of these segments, one can compute ...

  7. Spherical Earth - Wikipedia

    en.wikipedia.org/wiki/Spherical_Earth

    Image from space: The curved surface of the spherical planet Earth. Spherical Earth or Earth's curvature refers to the approximation of the figure of the Earth to a sphere.The concept of a spherical Earth gradually displaced earlier beliefs in a flat Earth during classical antiquity and the Middle Ages.

  8. Angle of incidence (optics) - Wikipedia

    en.wikipedia.org/wiki/Angle_of_incidence_(optics)

    In computer graphics and geography, the angle of incidence is also known as the illumination angle of a surface with a light source, such as the Earth's surface and the Sun. [1] It can also be equivalently described as the angle between the tangent plane of the surface and another plane at right angles to the light rays. [2]

  9. Gradient-index optics - Wikipedia

    en.wikipedia.org/wiki/Gradient-index_optics

    This index gradient causes refraction of light rays (at a shallow angle to the road) from the sky, bending them into the eye of the viewer, with their apparent location being the road's surface. The Earth's atmosphere acts as a GRIN lens, allowing observers to see the sun for a few minutes after it is actually below the horizon, and observers ...