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Optical phenomenon
Optical phenomenon
Optical phenomenon
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A 22° halo around the Moon in Atherton, California

Optical phenomena are any observable events that result from the interaction of light and matter.

All optical phenomena coincide with quantum phenomena.[1] Common optical phenomena are often due to the interaction of light from the Sun or Moon with the atmosphere, clouds, water, dust, and other particulates. One common example is the rainbow, when light from the Sun is reflected and refracted by water droplets. Some phenomena, such as the green ray, are so rare they are sometimes thought to be mythical.[2] Others, such as Fata Morganas, are commonplace in favored locations.

Other phenomena are simply interesting aspects of optics, or optical effects. For instance, the colors generated by a prism are often shown in classrooms.

A solar halo as seen from 41° south latitude

Scope

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Optical phenomena encompass a broad range of events, including those caused by atmospheric optical properties, other natural occurrences, man-made effects, and interactions involving human vision (entoptic phenomena). Also listed here are unexplained phenomena that could have an optical explanation and "optical illusions" for which optical explanations have been excluded.

There are multiple phenomena that result from either the particle or the wave nature of light. Some are quite subtle and observable only by precise measurement using scientific instruments. A famous example is the bending of starlight by the Sun during a solar eclipse, a phenomenon that serves as evidence for the curvature of space as predicted by the theory of relativity.

Atmospheric optics

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This section is an excerpt from List of atmospheric optical phenomena.[edit]
A circumzenithal arc over Grand Forks, North Dakota
The Belt of Venus over Paranal Observatory atop Cerro Paranal in the Atacama Desert, northern Chile[3]
Crepuscular rays at sunrise in Malibu, California

Atmospheric optical phenomena include:

A double rainbow at Minsi Lake, Pennsylvania
A sun pillar in Finistère, Brittany
Atmospheric optical phenomenon

Non-atmospheric optical phenomena

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Green flash appears above the solar disc for a second or so. One such occurrence was taken from Cerro Paranal.

Other optical effects

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Entoptic phenomena

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Main article: Entoptic phenomenon

Optical illusions

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Main article: Optical illusion

Unexplained phenomena

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See also: Forteana, Will-o'-the-wisp, and Unidentified flying object

Some phenomena are yet to be conclusively explained and may possibly be some form of optical phenomena.[4]

See also

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References

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Source

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Ozerov, Ruslan P.; Vorobyev, Anatoli A. (2007). "Wave Optics and Quantum–Optical Phenomena". Physics for Chemists. pp. 361–422. doi:10.1016/B978-044452830-8/50008-8. ISBN 978-0-444-52830-8.

Further reading

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Optical phenomenon

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from Grokipedia
Optical phenomena encompass the observable effects arising from the interactions of with and the surrounding environment, including processes such as reflection, , interference, , and polarization. These events occur due to the wave-like and particle-like properties of , as described by electromagnetic theory, and are central to the field of , which examines how propagates, scatters, and is manipulated in various media. Fundamental to physics, optical phenomena explain everyday visual experiences and underpin technologies like and . In natural settings, optical phenomena are vividly displayed through atmospheric interactions, where bends, scatters, or reflects off particles like droplets or ice crystals. For instance, rainbows form when sunlight undergoes , internal reflection, and dispersion within raindrops, producing a of colors with the primary bow exhibiting a radius of about 42 degrees. Halos, such as the common 22-degree halo around the sun or moon, result from through hexagonal ice crystals in high-altitude cirrus clouds, creating circular rings of . Mirages, optical illusions like the apparent "puddles" on hot roads, arise from caused by sharp temperature gradients in the air, which alter the and bend rays toward cooler layers. Beyond nature, optical phenomena drive numerous scientific and applications by exploiting light's behavior at interfaces and in materials. Reflection and , governed by laws like the angle of incidence equaling the angle of reflection and (nisin⁡θi=ntsin⁡θtn_i \sin \theta_i = n_t \sin \theta_t), enable imaging systems such as lenses and mirrors in cameras and telescopes. Interference patterns, observed in setups like the , reveal wave superposition and are crucial for precision measurements in and . , the bending of light around obstacles, limits resolution in optical instruments but also enables techniques like for studying atomic structures. Polarization, the orientation of light's , finds use in displays and glare-reducing , with effects like minimizing reflection for specific polarizations. These phenomena not only illuminate fundamental principles of wave but also continue to inspire advances in and quantum technologies, where controlling light- interactions at nanoscale levels yields innovations like photonic crystals and components.

Fundamentals

Definition and Scope

Optical phenomena refer to the observable effects arising from the interactions of with , encompassing processes such as , reflection, , , interference, and absorption. These manifestations are fundamentally visual or detectable within the , ultraviolet, or ranges, distinguishing them from non-optical electromagnetic interactions like those in radio waves or X-rays. The scope of optical phenomena is extensive, covering both natural occurrences—such as those in atmospheric or biological contexts—and artificial setups in laboratories or perceptual systems. Natural effects include light bending through atmospheric layers or in biological tissues, while artificial ones involve engineered devices like lenses or interferometers that exploit these principles for or . This broad purview excludes non-visual electromagnetic effects, focusing instead on 's behavior as rays, waves, or photons in interaction with media. Optical phenomena are classified according to underlying physical principles and environmental contexts. By principle, they fall into geometric optics (treating as rays for reflection and ), wave optics (addressing interference and via electromagnetic waves), and (incorporating photon-based effects like absorption and emission). By occurrence, they are grouped into atmospheric (e.g., light interactions with air or particles) and non-atmospheric (e.g., or biological settings) categories, providing a framework for systematic study.

Historical Overview

The earliest recorded observations of optical phenomena date back to , where , in the 4th century BCE, described rainbows and halos as reflections of sunlight from droplets and atmospheric particles in his work Meteorologica. These explanations, while qualitative, marked the initial attempts to rationalize atmospheric effects through natural causes rather than mythological interpretations. Around the 2nd century CE, advanced the study of in his Optics, conducting systematic measurements of bending at interfaces between air, , and , laying foundational empirical groundwork for understanding image distortion and atmospheric bending of . During the medieval and Renaissance periods, significant progress occurred in the Islamic world, particularly with Ibn al-Haytham's (completed around 1021 CE), which detailed the pinhole camera's formation of inverted images and refuted the emission theory of vision in favor of intromission, where light rays enter the eye from objects. This comprehensive treatise influenced European scholars and shifted optics toward experimental verification of . In the 17th through 19th centuries, European scientists built on these foundations with mechanistic models. Isaac Newton's 1666 prism experiments demonstrated the dispersion of white light into a , establishing that color arises from varying refractive indices rather than modification of a single hue. proposed the wave theory of light in 1678, explaining and reflection through secondary wavelets propagating in an . By 1801, Thomas Young's provided evidence of interference patterns, solidifying light's wave nature and challenging particle models. The 20th century introduced quantum perspectives, with Albert Einstein's 1905 explanation of the positing light as discrete quanta (photons), bridging wave and particle behaviors. emerged post-1920s through and , with seminal works by Dirac and others formalizing light-matter interactions at the quantum level. Modern milestones include the 1960 invention of the by , enabling coherent light for studying nonlinear phenomena like . From the 1980s onward, computational modeling advanced simulations of complex effects, such as and , via methods like complex ray tracing and finite-difference time-domain algorithms.

Principles of Optics

Geometric Optics

Geometric optics, also known as ray optics, approximates the behavior of light as straight-line rays propagating through space, ignoring its wave nature to model phenomena involving reflection, refraction, and image formation on macroscopic scales. This approach is particularly effective for systems where the wavelength of light is much smaller than the dimensions of optical elements, allowing for straightforward predictions of light paths using geometric constructions. The foundational principles stem from classical observations and experiments, enabling the analysis of everyday optical devices without delving into interference or diffraction effects. The law of reflection states that light rays incident on a surface obey the rule that the angle of incidence equals the angle of reflection, measured relative to the normal at the point of incidence, which holds for both plane and curved surfaces. This principle governs how mirrors produce images: specular reflection occurs on smooth surfaces like polished metal, where parallel incident rays reflect parallel to form clear virtual or real images, whereas diffuse reflection on rough surfaces scatters rays in multiple directions, preventing coherent image formation but enabling visibility of objects under illumination. For refraction, Snell's law quantifies the bending of rays at interfaces between media with different refractive indices: n1sin⁡θ1=n2sin⁡θ2n_1 \sin \theta_1 = n_2 \sin \theta_2, where nn is the refractive index and θ\theta the angle from the normal; this law, first accurately described by Ibn Sahl in 984 CE and later by Willebrord Snell in 1621, explains how light speed variations cause path deviations. Lenses manipulate to focus rays, with converging (convex) lenses bending parallel rays to a real focal point and diverging (concave) lenses spreading them to a virtual focus; for a in air, the ff is given by the lensmaker's equation 1f=(n−1)(1R1−1R2)\frac{1}{f} = (n-1)\left( \frac{1}{R_1} - \frac{1}{R_2} \right), where nn is the of the lens material and R1R_1, R2R_2 are the radii of of its surfaces. Prisms exploit to deviate rays by an dependent on their apex and material, and basic dispersion arises because varies with wavelength—shorter wavelengths (e.g., blue) bend more than longer ones (e.g., red)—separating white light into a spectrum without requiring wave interference. In applications, these principles enable image formation in cameras, where a convex lens focuses rays from distant objects onto a sensor plane to create sharp inverted real images, and in the human eye, where the cornea and crystalline lens similarly converge rays onto the retina for inverted real images that the brain interprets upright. Total internal reflection occurs when light in a denser medium strikes a boundary at an greater than the critical (θc=sin⁡−1(n2/n1)\theta_c = \sin^{-1}(n_2/n_1)), causing complete reflection; this underpins fiber optics, where cabled glass cores with cladding of lower guide signals over kilometers with minimal loss via repeated internal bounces. The in geometric holds when wavelengths are negligible compared to obstacle or sizes, accurately modeling in uniform media and interactions with large-scale elements like lenses or mirrors. However, it breaks down near edges or small openings, where causes ray spreading, necessitating wave for precise predictions in such regimes. This limitation highlights geometric as a high-frequency asymptotic to the full electromagnetic theory of .

Wave and Quantum Optics

Wave optics describes optical phenomena that arise from the wave nature of light, governed by the , which states that the resultant wave displacement at any point is the algebraic sum of the displacements from individual waves. This linear superposition enables key effects like interference and , which are prominent when light interacts with apertures or obstacles on scales comparable to its . Interference manifests as regions of enhanced or reduced intensity due to the coherent overlap of . In constructive interference, align in phase, amplifying the ; in destructive interference, out-of-phase cancel, minimizing intensity. For two coherent of equal , the resulting intensity follows I∝cos⁡2(δ2),I \propto \cos^2\left(\frac{\delta}{2}\right), where δ\delta is the phase difference between the . , meanwhile, refers to the spreading of beyond geometric shadows, explained by treating each point on a as a source of secondary wavelets. In single-slit , destructive interference produces minima at angles satisfying sin⁡θ=mλa,\sin \theta = \frac{m \lambda}{a}, with m=±1,±2,…m = \pm 1, \pm 2, \dots, λ\lambda the wavelength, and aa the slit width. Quantum optics extends these wave descriptions by incorporating light's particle-like duality, treating photons as discrete quanta with energy E=hνE = h \nu, where hh is Planck's constant and ν\nu the frequency. This quantization resolved inconsistencies in classical wave theory, such as the ultraviolet catastrophe in blackbody radiation. The photoelectric effect further illustrates this: light ejects electrons from a metal surface only if its frequency exceeds a material-specific threshold, with electron kinetic energy Ek=hν−ϕE_k = h \nu - \phi (where ϕ\phi is the work function), independent of intensity below the threshold. Einstein's explanation unified wave and particle views, earning him the 1921 Nobel Prize. Classic experiments highlight these principles. Young's double-slit experiment (1801) passes coherent through two narrow slits, producing an interference pattern of alternating bright and dark fringes on a screen, confirming light's wave nature through superposition. causes the iridescent colors in soap bubbles, where reflects from the inner and outer soap-water interfaces, undergoing a path-length-dependent phase shift that leads to constructive interference for certain wavelengths and destructive for others, varying with film thickness. (1923) demonstrates photon's particle : X-rays scattered by loosely bound electrons in light elements exhibit a wavelength increase Δλ=hmec(1−cos⁡θ)\Delta \lambda = \frac{h}{m_e c} (1 - \cos \theta), where mem_e is , cc , and θ\theta scattering angle, inconsistent with classical scattering but aligning with photon-electron collisions. Modern quantum optics explores non-classical effects like entanglement, where photon pairs generated via processes such as exhibit correlated polarizations that violate Bell's inequalities, as verified in Aspect's 1982 experiments using time-varying analyzers to close locality loopholes. These entangled states enable applications in quantum spectroscopy, where techniques like coherent control of atomic transitions achieve sub-Doppler resolution and precision measurements beyond classical limits, as in and frequency metrology.

Atmospheric Phenomena

Refraction-Based Effects

Refraction-based effects in the atmosphere arise from the gradual bending of light rays due to variations in air density, primarily caused by gradients in or . These gradients alter the of air, leading to optical distortions that create apparent displacements or multiple images of distant objects. Unlike abrupt at interfaces, atmospheric occurs continuously over extended paths, often spanning kilometers. Inferior mirages form when light rays from an object pass through a layer of warmer, less dense air near the ground, bending the rays upward away from the hotter region and producing an inverted image below the actual object, such as the shimmering "" seen on hot desert roads or highways. Superior mirages, in contrast, occur under temperature inversions where colder, denser air lies beneath warmer air, causing rays to bend downward and create erect or multiple images above the object, often elevating or distorting distant horizons. These effects rely on the principle of applied across varying media, as detailed in geometric optics. A prominent example of a superior mirage is the fata morgana, a complex, rapidly shifting display of stacked, distorted images resembling castles or ships, typically observed over cold water bodies like seas or lakes where strong inversions trap rays in a duct-like path. , another superior mirage variant, elevates the apparent height of distant objects such as mountains or ships, making them visible beyond the normal horizon when a steep exaggerates the downward of rays. The green flash at sunset represents a effect combined with chromatic dispersion: as the sun's upper rim dips below the horizon, the atmosphere's dispersion causes green to refract more than red , briefly isolating a green burst lasting one to two seconds under clear conditions. The of air, nn, varies with atmospheric conditions according to the empirical relation (n−1)×106≈77.6[P](/page/Pressure)[T](/page/Temperature)(n - 1) \times 10^6 \approx 77.6 \frac{[P](/page/Pressure)}{[T](/page/Temperature)} for dry air, where PP is in hPa and TT is in , reflecting the direct proportionality to air ; this leads to a change of about 10−610^{-6} per degree . In such gradients, rays follow curved paths with a roughly 6.6 to 7 times the Earth's radius under standard conditions, enabling the long-distance bending necessary for formation. These phenomena are prevalent in deserts, where intense surface heating drives strong inferior mirages, and in polar regions, where persistent cold layers foster superior mirages like the fata morgana. Historical accounts from explorations, such as the 1913-1917 , document mirages deceiving navigators by fabricating illusory landmasses, contributing to navigational errors in the early . Ice crystals in high-altitude cirrus clouds produce striking angular effects through their shapes, combining and to form halos and sundogs. The common appears as a white or faintly colored ring encircling the sun or , resulting from refracting through the 60° prism faces of randomly oriented plate or column crystals, with a angle of 22° due to the crystal's (∼1.31 for at visible wavelengths). Sundogs, or parhelia, manifest as bright spots at the 's 3 o'clock and 9 o'clock positions, formed when passes through horizontal plate crystals aligned parallel to the ground, refracting at the same 22° angle and red light inward toward the sun. These effects highlight crystals' role in particle-specific redirection, often accompanied by subtle polarization from the geometry.

Scattering and Diffraction Effects

Scattering and diffraction effects in the atmosphere arise primarily from interactions of or with small particles such as air molecules, , and droplets, redirecting light in ways that produce vivid color shifts and angular patterns. These phenomena differ from in smooth media by involving discrete particle-induced deviations, often leading to wavelength-selective dispersion. Rayleigh and dominate for molecular and aerosol interactions, respectively, while manifests in aureole-like rings around celestial bodies. Rayleigh scattering occurs when light interacts with particles much smaller than the wavelength, such as nitrogen and oxygen molecules in the air, resulting in elastic scattering that is highly wavelength-dependent. The scattered intensity is proportional to 1/λ41/\lambda^4, where λ\lambda is the wavelength, making shorter blue-violet light scatter far more efficiently than longer red light—by a factor of about 10 for visible wavelengths. This explains the blue color of the daytime sky, as blue light is diffused in all directions from overhead sunlight, while at sunset, the longer path through the atmosphere scatters away shorter wavelengths, leaving predominantly red hues to reach the observer. The Rayleigh scattering cross-section for such small spherical particles is given by σs=8π3k4a6∣m2−1m2+2∣2\sigma_s = \frac{8\pi}{3} k^4 a^6 \left| \frac{m^2 - 1}{m^2 + 2} \right|^2
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