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📘 After the shower, sunlight finds a screen of droplets

You step outside just after a shower. The Sun is behind your shoulder, rain still hangs in the air, and a band of colour appears across the darker sky ahead. The rainbow is not painted on a distant cloud: it is light arriving from many drop

3
lessons
~15 min
to learn
Adults
level
Start the course →

What you’ll learn

  1. A raindrop becomes a tiny prismTrace how refraction, dispersion, and internal reflection turn sunlight and water droplets into separated colours.A spherical raindrop acts like a curved prism and mirror: it bends sunlight in, separates wavelengths, reflects some light inside, and bends the colours back out.
  2. The arc is an angle, not an objectUse the Sun, droplet field, antisolar point, and viewing angle to explain the rainbow's arc and apparent movement.The primary bow is a geometric view centred opposite the Sun, usually seen as an arc because the ground hides the rest of its circular arrangement.
  3. Why rainbows come in pairsExplain secondary rainbows, spray rainbows, and fogbows as variations in ray paths and droplet conditions.Extra internal reflection creates a fainter, reversed secondary bow, while spray and tiny droplets change where and how sharply related optical effects appear.

Questions this course answers

Which sequence best describes the primary rainbow ray inside a raindrop?

A primary rainbow ray refracts as it enters water, reflects once inside the drop, and refracts again as it exits.

Put the viewing conditions for a primary rainbow in order from source to eye.

Sunlight must reach droplets in front of you, and the useful reflected and refracted rays then travel back toward your eyes from the opposite sky.

Match each feature with its optical cause.

The secondary bow is a distinct ray path through the same droplets, involving an extra internal reflection and a larger exit angle.

Why can two people standing near each other see slightly different rainbows?

A rainbow is a real optical effect, but it is not a solid object fixed to one place in the landscape.

Grounded in trusted sources

  • National Weather Service, How Do Rainbows Form?, https://www.weather.gov/fgz/Rainbow
  • National Weather Service, Rainbow glossary, https://forecast.weather.gov/glossary.php?word=Rainbow
  • UCAR Center for Science Education, The Appearance of the Sky, https://scied.ucar.edu/learning-zone/atmosphere/appearance-sky
  • UCAR Center for Science Education, Visible Light, https://scied.ucar.edu/learning-zone/atmosphere/visible-light
  • Met Office, I can make a rainbow, https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/weather/learn-about/met-office-for-schools/diy-activities/i-can-make-a-rainbow-diy-activity.pdf
  • Met Office, Rainbows: optical wonders, https://weather.metoffice.gov.uk/learn-about/weather/optical-effects/rainbows

Every Wunder lesson is built from real, reputable sources — never invented.

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