Glossary term: Refraction

Description: Refraction is the way that a wave – and, specifically, light – changes direction as it passes from one medium into another. The magnitude and direction of the change depends on the "indices of refraction" of the two media, which in turn depend on the speed of light in each medium, a relation that is encoded mathematically in Snell's law of refraction. The way that light passes into a piece of glass can be used to create a lens, which bundles parallel light rays – such as the light of a distant star – falling onto the lens. This is the main effect used in constructing refracting telescopes. Refraction also depends on the wavelength of the infalling light, a fact that can be used as in a prism, to separate light by wavelength into its constituent elementary colors – which is important for documenting and examining spectra.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

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A composite showing four rainbows. Each is centred on different points

24 Hours of Rainbow

Caption: This panoramic view taken with a smartphone of Livorno, Italy, showcases a series of vivid rainbows captured on three different days in December 2021. Rainbows are the result of sunlight being refracted by water droplets suspended in the air, typically after rainfall or during misty conditions. The water droplets act like a prism, breaking up (refracting) the sunlight into the various colours. The different wavelengths of light are refracted by different amounts, which is why we see this layering of colours. The photographer skillfully merged the most remarkable shots taken on different days to highlight the diverse sizes and brilliance of these rainbows. The locations at which the rainbows appear to be centred are different because each rainbow appeared when the Sun was at a different position in the sky. This composite image beautifully captures the transient yet mesmerising allure of rainbows, illustrating their fleeting appearance and gradual dissipation influenced by the shifting atmospheric conditions.
Credit: Fabrizio Guasconi/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons