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For an observer standing on the ground with h = 1.70 metres (5 ft 7 in), the horizon is at a distance of 4.7 kilometres (2.9 mi). 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).
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 ...
The observer never touches the horizon and never passes a location where it appeared to be. In the case of a horizon perceived by an occupant of a de Sitter universe, the horizon always appears to be a fixed distance away for a non-accelerating observer. It is never contacted, even by an accelerating observer.
In astronomy, coordinate systems are used for specifying positions of celestial objects (satellites, planets, stars, galaxies, etc.) relative to a given reference frame, based on physical reference points available to a situated observer (e.g. the true horizon and north to an observer on Earth's surface). [1]
A horizon is a boundary in spacetime satisfying prescribed conditions. There are several types of horizons that play a role in Albert Einstein 's theory of general relativity : Absolute horizon , a boundary in spacetime in general relativity inside of which events cannot affect an external observer
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Assume that the first observer uses coordinates labeled t, x, y, and z, while the second observer uses coordinates labeled t′, x′, y′, and z′. Now suppose that the first observer sees the second observer moving in the x-direction at a velocity v. And suppose that the observers' coordinate axes are parallel and that they have the same ...