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Apparent horizons depend on the "slicing" of a spacetime. That is, the location and even existence of an apparent horizon depends on the way spacetime is divided into space and time. For example, it is possible to slice the Schwarzschild geometry in such a way that there is no apparent horizon, ever, despite the fact that there is certainly an ...
The curvature of the horizon is easily seen in this 2008 photograph, taken from a Space Shuttle at an altitude of 226 km (140 mi). The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all ...
Event horizon, a boundary in spacetime beyond which events cannot affect the observer, thus referring to a black hole's boundary and the boundary of an expanding universe; Apparent horizon, a surface defined in general relativity; Cauchy horizon, a surface found in the study of Cauchy problems; Cosmological horizon, a limit of observability
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 ...
The cosmological horizon, also called the particle horizon or the light horizon, is the maximum distance from which particles can have traveled to the observer in the age of the universe. This horizon represents the boundary between the observable and the unobservable regions of the universe.
The apparent motion of an astronomical object (e.g. the Sun, a planet, or a distant star) around the two celestial poles in the Earth's night sky over the course of one day. Diurnal motion is caused by Earth's rotation about its own axis, such that every object appears to follow a circular path called the diurnal circle. double star
The boundary of the union of all trapped surfaces around a black hole is called an apparent horizon. A related term trapped null surface is often used interchangeably. However, when discussing causal horizons, trapped null surfaces are defined as only null vector fields giving rise to null surfaces. But marginally trapped surfaces may be ...
Additional horizons are associated with the possible future extent of observations, larger than the particle horizon owing to the expansion of space, an "optical horizon" at the surface of last scattering, and associated horizons with the surface of last scattering for neutrinos and gravitational waves.