rainbow

rainbow
Name	Rainbow
Caption	A multicolored atmospheric arc
Classification	Atmospheric optical phenomenon
Visibility	Worldwide
Primary	Sunlight, water droplets
Colors	Red, orange, yellow, green, blue, indigo, violet

rainbow A rainbow is an atmospheric optical phenomenon that appears as a multicolored arc caused by sunlight interacting with water droplets. It is observable after precipitation, near waterfalls, in spray from rivers or fountains, and in mist produced by waves, and it has been studied by scientists and depicted by artists, authors, religious leaders, and nations. Historical records from civilizations across Mesopotamia, Ancient Greece, China, and Maya civilization show early interest, while modern understanding developed through experiments by figures associated with Royal Society, Huygens, and Isaac Newton.

Physical formation

Rainbows form when sunlight encounters spherical water droplets suspended in the atmosphere, such as during rain showers or fog banks. Rays from a distant light source such as the Sun enter a single droplet, refract at the air-water interface, reflect internally, and refract again upon exit toward the observer's eye; these processes occur within countless droplets distributed along a conical surface with the observer at its apex. The angular radius of the primary arc is roughly determined by the refractive index of water and the geometry relative to the anti-solar point, a concept important to observers in meteorology and fieldworkers from institutions like the National Weather Service and Met Office. Secondary and tertiary arcs involve multiple internal reflections, shifting angular positions and intensity, phenomena investigated in experimental optics laboratories at universities such as University of Cambridge and Harvard University.

Optical explanation

Classical optical explanations combine geometric optics and wavelength-dependent dispersion. When white light from the Sun enters a droplet, dispersion separates colors because shorter wavelengths (blue, violet) refract more than longer wavelengths (red), producing an angular spread; this underpins spectral analysis used by researchers at facilities like the Cavendish Laboratory and Max Planck Institute for Physics. Interference and diffraction effects near droplet edges give rise to supernumerary arcs, a topic addressed by wave-optics treatments developed by theorists connected to Fresnel and Thomas Young. Polarization measurements reveal that light in primary and secondary bows is partially polarized, a property exploited by polarimetry teams at observatories including NOAA and European Space Agency for atmospheric remote sensing. Detailed ray-tracing methods implemented by research groups at California Institute of Technology and Massachusetts Institute of Technology quantify the intensity and angular distribution of bow components.

Types and variants

Several distinct manifestations are recognized by atmospheric scientists and photographers. Primary and secondary bows are the most common; tertiary and higher-order bows are rare but documented by observers at observatories such as Roque de los Muchachos Observatory and research stations like Mauna Kea. Double rainbows feature reversed color order in the outer arc, a fact noted in classical optics treatises by Christiaan Huygens and later textbooks from Cambridge University Press. Supernumerary rainbows arise from interference and require nearly uniform droplet size, a condition studied in cloud microphysics programs at National Center for Atmospheric Research. Other variants include reflection bows from surface-reflected light near lakes studied by limnologists at Scripps Institution of Oceanography, fogbows in maritime environments monitored by crews on vessels registered to Royal Navy and commercial fleets, and monochrome bows, such as red bows observed at sunrise or sunset, documented in field reports by national meteorological services.

Cultural significance

Rainbows feature prominently in myth, religion, art, and modern identity movements. In Norse mythology the rainbow bridge connects realms and appears in sagas preserved by scholars at institutions like University of Oslo; in Hebrew Bible narratives the phenomenon is associated with covenants in traditions studied at seminaries such as Hebrew Union College. Artists from Renaissance masters to modernists in collections at the Louvre and Tate Modern have incorporated the motif, while poets from William Wordsworth to Maya Angelou have used it symbolically. Scientific figures like Isaac Newton used prism experiments to connect optical spectra to bows, influencing curricula at University of Cambridge. In contemporary culture, the multicolored flag representing LGBTQ+ communities originated in designs by activists connected to movements in San Francisco and is displayed at events organized by institutions such as Stonewall.

Scientific study and measurements

Quantitative study of bows spans laboratory optics, field observation, and remote sensing. Spectrometers and imaging polarimeters deployed by teams at NOAA, NASA, and university groups measure angular spectra and polarization to validate scattering models. High-speed cameras and droplet generators in laboratories at Imperial College London and ETH Zurich reproduce supernumerary structures and quantify dependence on droplet size distribution, a parameter also central to cloud microphysics studies at World Meteorological Organization workshops. Computational models using Mie theory and T-matrix methods are maintained by research groups at Los Alamos National Laboratory and Jet Propulsion Laboratory to simulate scattering by spherical particles. Citizen science projects coordinated by societies such as the Royal Astronomical Society collect geolocated observations that complement satellite imagery from Copernicus Programme missions.

Occurrence and observation conditions

Observation requires a light source behind the observer and water droplets ahead, with the sun low in the sky to produce a large, visible arc; these geometric constraints are emphasized in field manuals from United States Geological Survey and national meteorological services. Brightness and visibility depend on droplet size distribution, sunlight intensity, and atmospheric clarity; photographers and researchers often use tripod-mounted cameras and calibrated photometers from manufacturers like Canon and Nikon for reproducible records. Accessible viewing sites include coastal cliffs near Cape Cod, waterfall trails at Iguazu Falls and Niagara Falls, and mountain passes in ranges such as the Himalayas, where altitude and mist enhance occurrence rates. Scientific campaigns coordinate observation windows with satellite overpasses involving platforms like Landsat and Sentinel to correlate ground-based measurements with remote sensing data.

Category:Atmospheric optical phenomena