CrowdScience How big is a rainbow?
Nov 28, 2025
Philip Laven, an independent rainbow expert, demonstrates how sunlight refracts and reflects in water droplets to create rainbows. Retired professor Raymond Lee explains that rainbows lack a fixed size, emphasizing their angular dimensions based on perspective. Aerial photographer Colin Leinhardt shares his experience capturing a stunning full circular rainbow from a helicopter, showcasing its unique beauty. The fascinating discussion reveals how context impacts our perception of a rainbow's size and introduces concepts like secondary rainbows and the 3D nature of these atmospheric wonders.
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How Rainbows Form At Specific Angles
- A rainbow forms when sunlight refracts into a drop, reflects inside, then refracts out, concentrating light at a specific angle.
- Different colours emerge because each wavelength refracts at slightly different angles producing the spectrum.
Rainbows Have A Fixed Angular Size
- A rainbow has a fixed angular size: roughly a 42° radius, so a full semicircle spans about 84° across your view.
- That angular size stays the same regardless of your distance or movement relative to the rain.
See Bigger Arcs At Low Sun Angles
- To see more of the semicircle, view a rainbow when the sun is low near sunrise or sunset.
- Aim for lower solar angles to maximise the visible portion of the rainbow arc.