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  2. Horizon - Wikipedia

    en.wikipedia.org/wiki/Horizon

    View of the ocean with two ships: one in the foreground and one to the left of it on the horizon. Historically, the distance to the visible horizon has long been vital to survival and successful navigation, especially at sea, because it determined an observer's maximum range of vision and thus of communication, with all the obvious consequences for safety and the transmission of information ...

  3. Observable universe - Wikipedia

    en.wikipedia.org/wiki/Observable_universe

    This would be the "light travel distance" (see Distance measures (cosmology)) rather than the "proper distance" used in both Hubble's law and in defining the size of the observable universe. Cosmologist Ned Wright argues against using this measure. [75] The proper distance for a redshift of 8.2 would be about 9.2 Gpc, [76] or about 30 billion ...

  4. Line-of-sight propagation - Wikipedia

    en.wikipedia.org/wiki/Line-of-sight_propagation

    Assuming a perfect sphere with no terrain irregularity, the distance to the horizon from a high altitude transmitter (i.e., line of sight) can readily be calculated. Let R be the radius of the Earth and h be the altitude of a telecommunication station. The line of sight distance d of this station is given by the Pythagorean theorem;

  5. Long distance observations - Wikipedia

    en.wikipedia.org/wiki/Long_distance_observations

    A typical example of long-distance observation. The Tatra Mountains as seen from the Łysa Góra, in southeast Poland, at a distance of about 200 km (120 mi).. Long-distance observation is any visual observation, for sightseeing or photography, that targets all the objects, visible from the extremal distance with the possibility to see them closely.

  6. Cosmological horizon - Wikipedia

    en.wikipedia.org/wiki/Cosmological_horizon

    The particle horizon, also called the cosmological horizon, the comoving horizon, or the cosmic light horizon, is the maximum distance from which light from particles could have traveled to the observer in the age of the universe. It represents the boundary between the observable and the unobservable regions of the universe, so its distance at ...

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

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

    Graphs of distances to the true horizon on Earth for a given height h. s is along the surface of Earth, d is the straight line distance, and ~d is the approximate straight line distance assuming h << the radius of Earth, 6371 km. In the SVG image, hover over a graph to highlight it.

  8. Event horizon - Wikipedia

    en.wikipedia.org/wiki/Event_horizon

    In astrophysics, an event horizon is a boundary beyond which events cannot affect an observer. Wolfgang Rindler coined the term in the 1950s. [1] In 1784, John Michell proposed that gravity can be strong enough in the vicinity of massive compact objects that even light cannot escape. [2] At that time, the Newtonian theory of gravitation and the ...

  9. Vanishing point - Wikipedia

    en.wikipedia.org/wiki/Vanishing_point

    For different sets of lines parallel to this plane α, their respective vanishing points will lie on this vanishing line. The horizon line is a theoretical line that represents the eye level of the observer. If the object is below the horizon line, its lines angle up to the horizon line. If the object is above, they slope down.