How to See a Rainbow
This is one of a set of almost 40 diagrams exploring Rainbows.
Each diagram appears on a separate page and is supported by a full explanation.
- Follow the links embedded in the text for definitions of all the key terms.
- For quick reference don’t miss the summaries of key terms further down each page.
How to See a Rainbow
TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
About the diagram
An overview of rainbows
- Atmospheric rainbows:
- Atmospheric rainbows often appear as a shower of rain is approaching, or has just passed over. The falling raindrops form a curtain on which sunlight falls.
- To see an atmospheric rainbow, the rain must be in front of the observer and the Sun must be in the opposite direction, at their back.
- A rainbow can form a complete circle when seen from a plane, but from the ground, an observer usually sees the upper half of the circle with the sky as a backdrop.
- Rainbows are curved because light is reflected, refracted and dispersed symmetrically around their centre-point.
- The centre-point of a rainbow is sometimes called the anti-solar point. ‘Anti’, because it is opposite the Sun with respect to the observer.
- An imaginary straight line can always be drawn that passes through the Sun, the eyes of an observer and the anti-solar point – the geometric centre of a rainbow.
- A section of a rainbow can easily disappear if anything gets in the way and forms a shadow. Hills, trees, buildings and even the shadow of an observer can cause a portion of a rainbow to vanish.
- Not all rainbows are ‘atmospheric’. They can be produced by waterfalls, lawn sprinklers and anything else that creates a fine spray of water droplets in the right conditions.
About the diagram
The weather, season and time of day are all important if you hope to see an atmospheric rainbow.
- The best rainbows appear in the morning and evening when the Sun is strong but low in the sky.
- Northern and southern latitudes away from the equator are good for rainbows because the Sun is lower at its zenith.
- Mountains and coastal areas can create ideal conditions because as air sweeps over them, it cools, condenses and falls as rain.
- Rainbows are rare in areas with little or no rainfall such as dry, desert conditions with few clouds.
- Too much cloud is not good because it blocks direct sunlight.
- Winter is not necessarily the best season because the light is weaker and there can be excessive cloud.
- Rainbows are less common around midday because the higher the Sun is in the sky the lower the rainbow.
- If the Sun is too high, then by the time the raindrops are in the right position to form part of a rainbow they are lost in the landscape.
Some key terms
- The Sun is the most important light source in our lives and emits every wavelength of light in the visible spectrum.
- Celestial sources of light include other stars, comets and meteors.
- Other natural sources of light include lightning, volcanoes and forest fires.
- There are also bio-luminescent light sources including some species of fish and insects as well as types of bacteria and algae.
- Man-made light sources of the most simple type include natural tars and resins, wax candles, lamps that burn oil, fats or paraffin and gas lamps.
- Modern man-made light sources include tungsten light sources. These are a type of incandescent source which means they radiate light when electricity is used to heat a filament inside a glass bulb.
- Halogen bulbs are more efficient and long-lasting versions of incandescent tungsten lamps and produce a very uniform bright light throughout the bulb’s lifetime.
- Fluorescent lights are non-incandescent sources of light. They generally work by passing electricity through a glass tube of gas such as mercury, neon, argon or xenon instead of a filament. These lamps are very efficient at emitting visible light, produce less waste heat, and typically last much longer than incandescent lamps.
- An LED (Light Emitting Diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor.
- Made-made lights can emit a single wavelength, bands of wavelengths or combinations of wavelengths.
- An LED light typically emits a single colour of light which is composed of a very narrow range of wavelengths.
- When sunlight is dispersed by rain and forms a rainbow, an observer often distinguishes red, orange, yellow, green, blue and violet bands of colour.
- Although an atmospheric rainbow contains electromagnetic waves with all possible wavelengths between red and violet, our eyes encounter difficulties in distinguishing between colours within specific regions of this spectrum. For example, all wavelengths between 520 to 570 nanometers may appear to be exactly the same green to most observers.
- As light travels from a fast medium such as air to a slow medium such as water it bends toward the normal and slows down.
- As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from the normal and speeds up.
- In a diagram illustrating optical phenomena like refraction or reflection, the normal is a line drawn at right angles to the boundary between two media.
- A fast (optically rare) medium is one that obstructs light less than a slow medium.
- A slow (optically dense) medium is one that obstructs light more than a fast medium.
- The speed at which light travels through a given medium is expressed by its index of refraction.
- If we want to know in which direction light will bend at the boundary between transparent media we need to know:
- Which is the faster, less optically dense (rare) medium with a smaller refractive index?
- Which is the slower, more optically dense medium with the higher refractive index?
- The amount that refraction causes light to change direction, and its path to bend, is dealt with by Snell’s law.
- Snell’s law considers the relationship between the angle of incidence, the angle of refraction and the refractive indices (plural of index) of the media on both sides of the boundary. If three of the four variables are known, then Snell’s law can calculate the fourth.
A rainbow is an optical effect produced by illuminated droplets of water. Rainbows are caused by reflection, refraction and dispersion of light in individual droplets and results in the appearance of an arc of spectral colours.
- Rainbows only appear when weather conditions are ideal and an observer is in the right place at the right time.
- Waterfalls, lawn sprinklers and other things that produce water droplets can produce a rainbow.
- A rainbow is formed from millions of individual droplets each of which reflects and refracts a tiny coloured image of the sun towards the observer.
- It is the dispersion of light as refraction takes place that produces the rainbow colours seen by an observer.
- When the sun is behind an observer then the rainbow will appear in front of them.
Diagrams are free to download
Downloads: Slides or Illustrations
- SLIDES are optimized for viewing on-screen.
- ILLUSTRATIONS are optimized for printing on A4 pages in portrait format.
- Slides are available in JPG and AI (Adobe Illustrator) file formats.
- Titles: Slides have titles.
- Backgrounds: Black.
- Size: 1686 x 1124 pixels (3:2 aspect ratio).
- Illustrations are available in JPG and AI two file formats.
- Titles: No titles.
- Backgrounds: White.
- Size: 1686 x 1124 (3:2 aspect ratio). So all illustrations reproduce at the same scale when inserted into Word documents etc.
- Labels: Calibri 24pt Italic.
File formats: JPG & AI
DOWNLOAD THE DIAGRAM ON THIS PAGE AS A JPG FILE
- JPG (JPEG) diagrams are 1686 x 1124 pixels (3:2 aspect ratio).
- If a JPG diagram doesn’t fit your needs, you can download it as an AI (Adobe Illustrator) file and edit it yourself.
- JPG files can be placed or pasted directly into MS Office documents.
DOWNLOAD THE DIAGRAM ON THIS PAGE AS AN AI file
- All AI (Adobe Illustrator) diagrams are 1686 x 1124 pixels (3:2 aspect ratio).
- All our diagrams are created in Adobe Illustrator as vector drawings.
- Save as or export AI files to other formats including PDF (.pdf), PNG (.png), JPG (.jpeg) and SVG(.svg) etc.
Spelling: UK & US
We use English (UK) spelling by default here at lightcolourvision.org.
COPY & PASTING TEXT
- After copy/pasting text please do a spell-check to change our spelling to match your own document.
- Download AI versions of diagrams to change the spelling or language used for titles, labels etc.
- We are adding American English (US) versions of diagrams on request. Just contact us and let us know what you need.
- When downloading JPG versions of diagrams, look out for JPG (UK) or JPG (US) in the download dialogue box.
Unless stated otherwise the author of all images and written content on lightcolourvision.org is Ric Mann.
ALL RIGHTS RESERVED
No part of this website may be copied, displayed, extracted, reproduced, utilised, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical or otherwise including but not limited to photocopying, recording, or scanning without the prior written permission of MediaStudies Trust.
Exceptions to the above statement are made for personal, educational and non-profit purposes:
Before downloading, cutting and pasting or reproducing any information, images or other assets found on lightcolourvision.org we ask you to agree to the following terms:
- All information, images and other assets displayed and made available for download on the lightcolourvision.org website are copyright. This means there are limitations on how they can be used.
- All information, images and other assets displayed or made available for download are solely and exclusively to be used for personal, educational and non-profit purposes.
- When you find the resources you need, then part of the download process involves you (the user) ticking a box to let us (at lightcolourvision.org) know we both agree on how the material can be used.
- Please contact [email protected] before considering any use not covered by the terms of the agreement above.
The copyright to all information, images and all other assets (unless otherwise stated) belongs to:
We love feedback
We welcome your feedback 🙂