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July 27, 2026Short & citedBlog
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Field Notes • Meteorology

Rainbow

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

Updated July 27, 20261 min readCited sources

A rainbow is an optical and meteorological phenomenon caused by refraction, internal reflection, and dispersion of light in water droplets. It typically appears as a multicoloured arc opposite the Sun.

What it is

A rainbow forms when sunlight enters water droplets, bends (refracts), reflects off the inside surface, and bends again as it exits. Different wavelengths of light bend by different amounts, splitting the light into a spectrum of colours. The visible sequence is red on the outer edge and violet on the inner edge.

Why it matters

Rainbows are not physical objects; their appearance depends on the observer’s position and the light source. They are studied in optics and meteorology as examples of light behaviour in small droplets, illustrating refraction, internal reflection, and dispersion in the atmosphere.

Key details

The most familiar rainbow is produced by sunlight and raindrops, but similar arcs can form in fog, sea spray, and waterfalls. Rainbows are seen opposite the Sun, with the Sun behind the observer and water droplets in front. The arc is part of a larger circle; from the ground, usually only the upper portion is visible.

In short

  • Rainbows form when light refracts, reflects, and disperses in water droplets.
  • They are optical phenomena, not physical objects at a fixed location.
  • The colour order is red on the outside, violet on the inside.
  • Rainbows can appear in mist, fog, spray, and dew, not just rain.
Canadian angle

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]

Quick 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.
Can rainbows form without rain?
Yes. Rainbows can also form in mist, fog, sea spray, waterfalls, and other airborne water droplets.

Sources

  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