The Canadian Encyclopedia — neutral, cited, updated
July 26, 2026Sources cited
Canadianwire.
Canada’s encyclopedia & explainer
Home›Science & Nature›Meteorology›Rainbow
Science & Nature • Meteorology

Rainbow

A rainbow is an optical and meteorological phenomenon caused by the refraction, internal reflection, and dispersion of light in water droplets.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

A rainbow is an optical and meteorological phenomenon caused by the refraction, internal reflection, and dispersion of light in water droplets. It usually appears as a multicoloured arc in the sky when sunlight shines on droplets of rain, mist, spray, or dew, and it is seen in the direction opposite the Sun.

Formation

Rainbows form when light enters water droplets, slows and refracts, reflects off the inside surface, and refracts again as it exits. Different wavelengths bend by different amounts, producing the visible colour spectrum.

Appearance and geometry

A rainbow is commonly seen as a circular or semicircular arc, but it is actually part of a full circle centred on the antisolar point. Its exact appearance changes with the observer’s position and the Sun’s angle.

Types and conditions

The best-known type is the primary rainbow produced by sunlight and raindrops, but similar arcs can form in fog, spray, mist, and other airborne water droplets. Rainbows require both light and suspended water droplets.

Scientific significance

Rainbows are studied in optics and meteorology as examples of light behaviour in small droplets. They illustrate refraction, internal reflection, and dispersion in the atmosphere.

Key facts

  • A rainbow is an optical phenomenon caused by refraction, internal reflection, and dispersion of light in water droplets.
  • It appears as a multicoloured arc opposite the Sun, with red on the outer edge and violet on the inner edge.
  • Rainbows depend on the observer’s position and are not physical objects at a fixed location.
  • They can form in rain, mist, fog, spray, and dew, not only in rain.
  • The visible colour order is typically red, orange, yellow, green, blue, indigo, and violet.
🍁
Canadian context

Rainbows are commonly observed across Canada after rain, in fog, and near waterfalls, making them a familiar part of Canadian weather and landscape. They also appear in Canadian science education as an example of atmospheric optics.[4][6][16]

Frequently asked questions

What causes a rainbow?
A rainbow is caused by sunlight interacting with water droplets through refraction, internal reflection, and dispersion of light.
Why does a rainbow appear opposite the Sun?
The observer sees the rainbow in the direction opposite the Sun because the light is redirected back toward the viewer from droplets in front of them.
Is a rainbow a real object?
No. A rainbow is an optical phenomenon, not a physical object located in one place.
Can rainbows form without rain?
Yes. Rainbows can also form in mist, fog, sea spray, waterfalls, and other airborne water droplets.
Why are the colours arranged in a certain order?
Different wavelengths of light bend by different amounts in water droplets, so red appears on the outside and violet on the inside.

References

  1. Wikipedia — https://en.wikipedia.org/wiki/Rainbow
    Supports: Definition; formation by refraction, internal reflection, and dispersion; appearance opposite the Sun; sources of airborne water
  2. Encyclopaedia Britannica — https://www.britannica.com/science/rainbow-atmospheric-phenomenon
    Supports: Definition; formation; direction opposite the Sun
  3. National Weather Service — https://www.weather.gov/fgz/Rainbow
    Supports: How rainbows form; circular arc explanation
  4. National Geographic Education — https://education.nationalgeographic.org/resource/rainbow/
    Supports: Optical phenomenon; 42-degree angle; not fixed in a specific place
  5. NOAA NESDIS — https://www.nesdis.noaa.gov/about/k-12-education/optical-phenomena/what-causes-rainbow
    Supports: Sunlight and atmospheric conditions; light entering droplets; not a thing in a specific place
  6. Royal Meteorological Society — https://www.rmets.org/metmatters/how-are-rainbows-formed
    Supports: Refraction, reflection, colour order, observer position, and angle conditions