Glossary term: Rainbow

Description: The huge arc or bow with concentric stripes in the colors violet, indigo, blue, green, yellow, orange, and red, spread out across the sky, usually visible after it has rained, is called a rainbow. When an observer sees a rainbow, the Sun is at the observer's back. A rainbow occurs because the small droplets of water in the air break up the white sunlight into the color spectrum through a process called dispersion due to refraction; this is similar to how a prism works. In a normal rainbow, light is reflected once within the water droplets as well as being dispersed through refraction.

Sometimes, two nested rainbows can be seen, where the colors in the second rainbow are in reverse order. The inner, brighter one is called the primary rainbow while the outer, fainter one is the secondary rainbow. This double rainbow phenomenon is relatively uncommon. The secondary rainbow occurs when light undergoes reflection twice within the water droplets in addition to refraction.

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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".

Related Media

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

Related Activities

Reading the Rainbow

Reading the Rainbow

astroEDU educational activity (links to astroEDU website)
Description: By understanding how rainbows work, you can discover about light and its properties, learning about stars, nebulae, galaxies, and our Universe.

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

Age Ranges: 14-16 , 16-19 , 19+
Education Level: Informal , Middle School , Secondary , University
Areas of Learning: Interactive Lecture , Observation based , Social Research
Costs: Low Cost
Duration: 1 hour 30 mins
Group Size: Group
Skills: Analysing and interpreting data , Asking questions , Engaging in argument from evidence