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  2. Horizon - Wikipedia

    en.wikipedia.org/wiki/Horizon

    To compute the greatest distance D BL at which an observer B can see the top of an object L above the horizon, simply add the distances to the horizon from each of the two points: D BL = D B + D L For example, for an observer B with a height of h B =1.70 m standing on the ground, the horizon is D B =4.65 km away.

  3. 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 ...

  4. Event horizon - Wikipedia

    en.wikipedia.org/wiki/Event_horizon

    The proper distance to the horizon is finite, [20] so the length of rope needed would be finite as well, but if the rope were lowered slowly (so that each point on the rope was approximately at rest in Schwarzschild coordinates), the proper acceleration experienced by points on the rope closer and closer to the horizon would approach infinity ...

  5. Line-of-sight propagation - Wikipedia

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

    The radio horizon of the transmitting and receiving antennas can be added together to increase the effective communication range. Radio wave propagation is affected by atmospheric conditions, ionospheric absorption, and the presence of obstructions, for example mountains or trees. Simple formulas that include the effect of the atmosphere give ...

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

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

    For example, ships travelling on large bodies of water (such as the ocean) disappear over the horizon progressively, such that the highest part of the ship can still be seen even when lower parts cannot, proportional to distance from the observer. Likewise, in the days of sailing ships, a sailor would climb up a mast to see farther.

  7. Horizon (general relativity) - Wikipedia

    en.wikipedia.org/wiki/Horizon_(general_relativity)

    Cauchy horizon, a surface found in the study of Cauchy problems; Cosmological horizon, a limit of observability; Killing horizon, a null surface on which there is a Killing vector field; Particle horizon, the maximum distance from which particles can have travelled to an observer in the age of the universe

  8. Horizontal coordinate system - Wikipedia

    en.wikipedia.org/wiki/Horizontal_coordinate_system

    Azimuth is measured eastward from the north point (sometimes from the south point) of the horizon; altitude is the angle above the horizon. The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane to define two angles of a spherical coordinate system: altitude and azimuth.

  9. Radar horizon - Wikipedia

    en.wikipedia.org/wiki/Radar_horizon

    The radar horizon is a critical area of ... the radar horizon would be the geometrical distance ... And for the same examples : the radar horizon for the radar at a 1 ...