These he plotted on a chart and drew a line for the apparent horizon.

More specific types of horizon include the related but distinct absolute and apparent horizons found around a black hole.

For example, important distinctions must be made between absolute horizons and apparent horizons.

Trapped null surfaces are used in the definition of the apparent horizon which typically surrounds a black hole.

In the particle's reference frame, there appears to be a boundary behind it from which no signals can escape (an apparent horizon).

Any apparent horizon is observer dependent.

The flowing landscape slowed with its appearance, stopped with the mountain barely over the apparent horizon, then reversed itself.

Apparent horizons are not invariant properties of a spacetime.

Note, however, that a black hole is defined with respect to the event horizon, which is not always the same as the apparent horizon.

Apparent horizons depend on the "slicing" of a spacetime.

The notion of an apparent horizon begins with the notion of a trapped null surface.

"Apparent Horizon"

Under these conditions, an apparent horizon is present in the particle's (accelerating) reference frame, representing a boundary beyond which events are unobservable.

The advantage is that this notion of a horizon is very geometrical, and does not depend on the observer, unlike apparent horizons, for example.

In the simple picture of stellar collapse leading to formation of a black hole, an event horizon forms before an apparent horizon.

That is, the location and even existence of an apparent horizon depends on the way spacetime is divided into space and time.

Because the Earth's surface is curved, the 'true horizon' (the line dividing the ground and the sky) is lower than this apparent horizon.

The apparent horizon came closer at last, growing brighter as it came until it gleamed like a white-hot gash against the clouds.

The apparent horizon is then defined as the boundary of these surfaces - essentially, it is the outermost surface of the black hole, in this sense.

Much confusion seems to arise concerning the differences between an apparent horizon (AH) and an event horizon (EH).

The apparent horizon (marginally outer trapped surface) is a minimal hypersurface, linking the theory of black holes to minimal surfaces and the Plateau problem.

In practice the apparent horizon has a negative altitude, whose absolute value gets larger as the observer ascends higher above sea level, due to the curvature of the Earth.

Chesley Bonestell did not like Aristarchus; it did not have the shape he wanted, nor the height of Crater wall, nor the distance to apparent horizon.

Yungui Gong and Anzhong Wang, The Friedmann equations and thermodynamics of apparent horizons, Phys.

In this case, nonnegative scalar curvature is replaced with the dominant energy condition, and one possibility is to replace the minimal surface condition with an apparent horizon condition.