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For an observer standing on the ground with h = 2 metres (6 ft 7 in), the horizon is at a distance of 5 kilometres (3.1 mi). For an observer standing on a hill or tower 30 metres (98 ft) above sea level, the horizon is at a distance of 19.6 kilometres (12.2 mi).
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 ...
Each observer measures their distance to the nearest observer in the chain, and the length of the chain, the sum of distances between nearby observers, is the total proper distance. [ 7 ] It is important to the definition of both comoving distance and proper distance in the cosmological sense (as opposed to proper length in special relativity ...
Altitude (alt.), sometimes referred to as elevation (el.) or apparent height, is the angle between the object and the observer's local horizon. For visible objects, it is an angle between 0° and 90°. [b] Azimuth (az.) is the angle of the object around the horizon, usually measured from true north and increasing eastward.
The horizontal, or altitude-azimuth, system is based on the position of the observer on Earth, which revolves around its own axis once per sidereal day (23 hours, 56 minutes and 4.091 seconds) in relation to the star background. The positioning of a celestial object by the horizontal system varies with time, but is a useful coordinate system ...
By subtracting this figure from 90°, he would find that the zenith distance of the Sun is 0°, which is the same as his latitude. If Observer B is standing at one of the geographical poles (latitude 90°N or 90°S), he would see the Sun on the horizon at an altitude of 0°.
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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