Optical phenomena in the context of "Opalescence"

In meteorology, an afterglow is an optical phenomenon, generally referring to a broad arch of whitish or pinkish sunlight in the twilight sky after sunset, consisting of purple light and bright segment. It consists of several atmospheric optical phenomena. The purple light mainly occurs when the Sun is 2–6° below the horizon, during civil twilight (from sunset to civil dusk), while the bright segment lasts until the end of the nautical twilight. Similarly, a foreglow is a broad arch of whitish or pinkish sunlight in the twilight sky before sunrise, consisting of purple light and bright segment.

Afterglow is often seen in volcanic eruptions, in which the purple light might also be called volcanic purple light. In volcanic occurrences specifically, the light is scattered by fine particulates, like dust, suspended in the atmosphere. Afterglow may refer to the golden-red glowing light from the sunset and sunrise reflected in the sky in alpenglow (similar to the Belt of Venus) and in particularly for its last stage, when the purple light is reflected.

Light scattering by particles is the process by which small particles (e.g. ice crystals, dust, atmospheric particulates, cosmic dust, and blood cells) scatter light causing optical phenomena such as the blue color of the sky, and halos.

Maxwell's equations are the basis of theoretical and computational methods describing light scattering, but since exact solutions to Maxwell's equations are only known for selected particle geometries (such as spherical), light scattering by particles is a branch of computational electromagnetics dealing with electromagnetic radiation scattering and absorption by particles.

A mirage is a naturally occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French (se) mirer, from the Latin mirari, meaning "to look at, to wonder at".

Mirages can be categorized as "inferior" (meaning lower), "superior" (meaning higher) and "Fata Morgana", one kind of superior mirage consisting of a series of unusually elaborate, vertically stacked images, which form one rapidly changing mirage.

The antisolar point is the abstract point on the celestial sphere directly opposite the Sun from an observer's perspective. This means that the antisolar point lies above the horizon when the Sun is below it, and vice versa. On a sunny day, the antisolar point can be easily found; it is located within the shadow of the observer's head. Like the zenith and nadir, the antisolar point is not fixed in three-dimensional space, but is defined relative to the observer. Each observer has an antisolar point that moves as the observer changes position.

The antisolar point forms the geometric center of several optical phenomena, including subhorizon haloes, rainbows, glories, the Brocken spectre, and heiligenschein. Occasionally, around sunset or sunrise, anticrepuscular rays appear to converge toward the antisolar point near the horizon. However, this is an optical illusion caused by perspective; in reality, the "rays" (i.e. bands of shadow) run near-parallel to each other.

A false sunrise is any of several atmospheric optical phenomena in which the Sun appears to have risen, but is actually still some distance below the horizon. A number of different atmospheric conditions can be responsible for this effect, all of which divert the sunlight in such a way as to allow it to reach the observer's eye, thereby giving the impression that the light comes directly from the Sun itself. The spread of light can sometimes resemble that of the true sun.

Several atmospheric phenomena that may alternatively be called a "false sunrise" are:

A false sunset can refer to one of two related atmospheric optical phenomena: (1) the Sun appears to be setting into or to have set below the horizon while it is actually still some height above the horizon; or (2) the Sun has already set below the horizon, but still appears to be on or above the horizon (thus representing the reverse of a false sunrise). Depending on the circumstances, these phenomena can give the impression of an actual sunset.

There are several atmospheric conditions which may cause the effect, most commonly a type of halo, caused by the reflection and refraction of sunlight by small ice crystals in the atmosphere, often in the form of cirrostratus clouds. Depending on which variety of "false sunset" is meant, the halo has to appear either above the Sun (which itself is hidden below the horizon) or below it (in which case the real Sun is obstructed from view, e.g. by clouds or other objects), making the upper and lower tangent arcs, upper and lower sun pillars and the subsun the most likely candidates.