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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Atmospheric optics | 1/5 | https://en.wikipedia.org/wiki/Atmospheric_optics | reference | science, encyclopedia | 2026-05-05T14:32:13.838616+00:00 | kb-cron |
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. Meteorological optical phenomena, as described in this article, are concerned with how the optical properties of Earth's atmosphere cause a wide range of optical phenomena and visual perception phenomena. Examples of meteorological phenomena include:
The blue color of the sky. This is from Rayleigh scattering, which sends more higher frequency/shorter wavelength (blue) sunlight into the eye of an observer than other frequencies/wavelength. The reddish color of the Sun when it is observed through a thick atmosphere, as during a sunrise or sunset. This is because long-wavelength (red) light is scattered less than blue light. The red light reaches the observer's eye, whereas the blue light is scattered out of the line of sight. Other colours in the sky, such as glowing skies at dusk and dawn. These are from additional particulate matter in the sky that scatter different colors at different angles. Halos, afterglows, coronas, polar stratospheric clouds, and sun dogs. These are from scattering, or refraction, by ice crystals and from other particles in the atmosphere. They depend on different particle sizes and geometries. Mirages. These are optical phenomena in which light rays are bent due to thermal variations in the refractive index of air, producing displaced or heavily distorted images of distant objects. Other optical phenomena associated with this include the Novaya Zemlya effect, in which the Sun has a distorted shape and rises earlier or sets later than predicted. A spectacular form of refraction, called the Fata Morgana, occurs with a temperature inversion, in which objects on the horizon or even beyond the horizon (e.g. islands, cliffs, ships, and icebergs) appear elongated and elevated, like "fairy tale castles". Rainbows. These result from a combination of internal reflection and dispersive refraction of light in raindrops. Because rainbows are seen on the opposite side of the sky from the Sun, rainbows are more visible the closer the Sun is to the horizon. For example, if the Sun is overhead, any possible rainbow appears near an observer's feet, making it hard to see, and involves very few raindrops between the observer's eyes and the ground, making any rainbow very sparse. Other phenomena that are remarkable because they are forms of visual illusions include:
Crepuscular rays, Anticrepuscular rays, and The apparent size of celestial objects such as the Sun and Moon.
== History == A book on meteorological optics was published in the sixteenth century, but there have been numerous books on the subject since about 1950. The topic was popularised by the wide circulation of a book by Marcel Minnaert, Light and Color in the Open Air, in 1954.
== Sun and Moon size ==
In the Book of Optics (1011–22 AD), Ibn al-Haytham argued that vision occurs in the brain, and that personal experience has an effect on what people see and how they see, and that vision and perception are subjective. Arguing against Ptolemy's refraction theory for why people perceive the Sun and Moon larger at the horizon than when they are higher in the sky, he redefined the problem in terms of perceived, rather than real, enlargement. He said that judging the distance of an object depends on there being an uninterrupted sequence of intervening bodies between the object and the observer. Critically, Ibn al-Haytham said that judging the size of an object depends on its judged distance: an object that appears near appears smaller than an object having the same image size on the retina that appears far. With the overhead Moon, there is no uninterrupted sequence of intervening bodies. Hence it appears far and small. With a horizon Moon, there is an uninterrupted sequence of intervening bodies: all the objects between the observer and the horizon, so the Moon appears far and large. Through works by Roger Bacon, John Pecham, and Witelo based on Ibn al-Haytham's explanation, the Moon illusion gradually came to be accepted as a psychological phenomenon, with Ptolemy's theory being rejected in the 17th century. For over 100 years, research on the Moon illusion has been conducted by vision scientists who invariably have been psychologists specializing in human perception. After reviewing the many different explanations in their 2002 book The Mystery of the Moon Illusion, Ross and Plug concluded "No single theory has emerged victorious".
== Sky coloration ==