Antonio de Ulloa y de la Torre-Guiral was a Spanish Navy officer. He spent much of his career in the Americas, where he carried out important scientific work. He also served the Spanish Empire as an administrator in the Viceroyalty of Peru and in Spanish Louisiana.
A halo is an optical phenomenon produced by light interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky. Many of these appear near the Sun or Moon, but others occur elsewhere or even in the opposite part of the sky. Among the best known halo types are the circular halo, light pillars, and sun dogs, but many others occur; some are fairly common while others are extremely rare.
Anticrepuscular rays, or antisolar rays, are meteorological optical phenomena similar to crepuscular rays, but appear opposite the Sun in the sky. Anticrepuscular rays are essentially parallel, but appear to converge toward the antisolar point, the vanishing point, due to a visual illusion from linear perspective.
A sunbeam, in meteorological optics, is a beam of sunlight that appears to radiate from the position of the Sun. Shining through openings in clouds or between other objects such as mountains and buildings, these beams of particle-scattered sunlight are essentially parallel shafts separated by darker shadowed volumes. Their apparent convergence in the sky is a visual illusion from linear perspective. The same illusion causes the apparent convergence of parallel lines on a long straight road or hallway at a distant vanishing point. The scattering particles that make sunlight visible may be air molecules or particulates.
Atmospheric diffraction is manifested in the following principal ways:
A Brocken spectre, also called Brocken bow, mountain spectre, or spectre of the Brocken is the magnified shadow of an observer cast in mid air upon any type of cloud opposite a strong light source. The figure's head can be surrounded by a bright area called Heiligenschein, or halo-like rings of rainbow-coloured light forming a glory, which appear opposite the Sun's direction when uniformly sized water droplets in clouds refract and backscatter sunlight.
Heiligenschein is an optical phenomenon in which a bright spot appears around the shadow of the viewer's head in the presence of dew. In photogrammetry and remote sensing, it is more commonly known as the hotspot. It is also occasionally known as Cellini's halo after the Italian artist and writer Benvenuto Cellini (1500–1571), who described the phenomenon in his memoirs in 1562.
In meteorology, a corona is an optical phenomenon produced by the diffraction of sunlight or moonlight by individual small water droplets and sometimes tiny ice crystals of a cloud or on a foggy glass surface. In its full form, a corona consists of several concentric, pastel-colored rings around the celestial object and a central bright area called an aureole. The aureole is often the only visible part of the corona and has the appearance of a bluish-white disk which fades to reddish-brown towards the edge. The angular diameter of a corona depends on the sizes of the water droplets involved; smaller droplets produce larger coronae. For the same reason, the corona is the most pronounced when the size of the droplets is most uniform. Coronae differ from halos in that the latter are formed by refraction from comparatively large rather than small ice crystals.
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.
Pambamarca is an eroded stratovolcano in the Central Cordillera of the northern Ecuadorian Andes in Pichincha Province. it is 25 miles (40 km) northeast of Quito. The summit is at an elevation of 4,062 metres (13,327 ft).
A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the Sun. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew.
A fog bow, sometimes called a white rainbow, is a similar phenomenon to a rainbow; however, as its name suggests, it appears as a bow in fog rather than rain. Because of the very small size of water droplets that cause fog—smaller than 0.05 millimeters (0.0020 in)—the fog bow has only very weak colors, with a red outer edge and bluish inner edge. The colors fade due to being smeared out by the diffraction effect of the smaller droplets.
A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent diameter of approximately 22° around the Sun or Moon. Around the Sun, it may also be called a sun halo. Around the Moon, it is also known as a moon ring, storm ring, or winter halo. It forms as sunlight or moonlight is refracted by millions of hexagonal ice crystals suspended in the atmosphere. Its radius, as viewed from Earth, is roughly the length of an outstretched hand at arm's length.
Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon. The colors resemble those seen in soap bubbles and oil on a water surface. It is a type of photometeor. This fairly common phenomenon is most often observed in altocumulus, cirrocumulus, lenticular, and cirrus clouds. They sometimes appear as bands parallel to the edge of the clouds. Iridescence is also seen in the much rarer polar stratospheric clouds, also called nacreous clouds.
The opposition surge is the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer. The term is most widely used in astronomy, where generally it refers to the sudden noticeable increase in the brightness of a celestial body such as a planet, moon, or comet as its phase angle of observation approaches zero. It is so named because the reflected light from the Moon and Mars appear significantly brighter than predicted by simple Lambertian reflectance when at astronomical opposition. Two physical mechanisms have been proposed for this observational phenomenon: shadow hiding and coherent backscatter.
The aureole effect or water aureole is an optical phenomenon similar to Heiligenschein, creating sparkling light and dark rays radiating from the shadow of the viewer's head. This effect is seen only over a rippling water surface. The waves act as lenses to focus and defocus sunlight: focused sunlight produces the lighter rays, while defocused sunlight produces the darker rays. Suspended particles in the water help make the aureole effect more pronounced. The effect extends a greater angular distance from the viewer's shadow when the viewer is higher above the water, and can sometimes be seen from a plane.
Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes .... [including] temporal and spatial resolutions beyond those discernible with the naked eye". Meteorological optics is "that part of atmospheric optics concerned with the study of patterns observable with the naked eye". Nevertheless, the two terms are sometimes used interchangeably.
Optical phenomena are any observable events that result from the interaction of light and matter.
