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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. Particle horizon - Wikipedia

    en.wikipedia.org/wiki/Particle_horizon

    The particle horizon (also called the cosmological horizon, the comoving horizon (in Scott Dodelson's text), 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.

  5. 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 ...

  6. 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;

  7. Radar horizon - Wikipedia

    en.wikipedia.org/wiki/Radar_horizon

    The radar horizon is a critical area of performance for aircraft detection systems, defined by the distance at which the radar beam rises enough above the Earth's surface to make detection of a target at the lowest level possible.

  8. 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.

  9. 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