Rainbows Seen From the Ground

Yes! A rainbow can form a complete circle when seen from a plane.

No! Rainbows are not always visible at midday because their whole circumference can be below the horizon when the sun is high in the sky.

Rainbows are sometimes represented as cones of colour because raindrops from directly in front of an observer to those in the far distance can all help to produce the resulting bows of colour.

Rainbows appear as bands of colour because our eyes tend to see some wavelengths of light as being brighter and so more distinct than others.

Rainbows appear when bright sunshine is refracted, reflected and dispersed in raindrops in the presence of an observer.

A human observer is a person who engages in observation by watching things.

• In the presence of visible light, an observer perceives colour because the retina at the back of the human eye is sensitive to wavelengths of light that fall within the visible part of the electromagnetic spectrum.
• The visual experience of colour is associated with words such as red, blue, yellow, etc.
• The retina’s response to visible light can be described in terms of wavelength, frequency and brightness.
• Other properties of the world around us must be inferred from light patterns.
• An observation can take many forms such as:
  • Watching an ocean sunset or the sky at night.
  • Studying a baby’s face.
  • Exploring something that can’t be seen by collecting data from an instrument or machine.
  • Experimenting in a laboratory setting.

 

A light source is a natural or man-made object that emits one or more wavelengths of light.

• 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.

Visible light refers to the range of wavelengths of electromagnetic radiation that is perceived as colour by human observers. While the range of visible light is generally considered to be 400-700 nm, the exact range of colours perceptible can vary slightly between individuals.

• Visible light is one form of electromagnetic radiation. Other forms of electromagnetic radiation include radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays. Visible light ranges from approximately 400 nanometres (nm) for violet to 700 nm for red.
• A human observer perceives visible light as a combination of all the spectral colours between red and violet, as well as a vast range of other colours produced from the blending of different wavelengths in varying proportions.

The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.

• As light travels through the air it is invisible to our eyes.
• Human beings don’t see wavelengths of light, but they do see the spectral colours that correspond with each wavelength and colours produced when different wavelengths are combined.
• The visible spectrum includes all the spectral colours between red and violet and each is produced by a single wavelength.
• The visible spectrum is often divided into named colours, though any division of this kind is somewhat arbitrary.
• Traditional colours referred to in English include red, orange, yellow, green, blue, and violet.

White light is the term for visible light that contains all wavelengths of the visible spectrum at equal intensities.

• The sun emits white light because sunlight contains all the wavelengths of the visible spectrum in roughly equal proportions.
• Light travelling through a vacuum or a medium is termed white light if it includes all wavelengths of visible light.
• Light travelling through a vacuum or air is not visible to our eyes unless it interacts with something.

• The term white light can have two meanings:
  • It can refer to a combination of all wavelengths of visible light travelling through space, regardless of observation.
  • What a person sees when all colours of the visible spectrum hit a white or neutral-coloured surface.

A rainbow is an optical effect produced by illuminated droplets of water. Rainbows are caused by reflection, refraction (bending) and dispersion (spreading out) of light in individual droplets and result in the appearance of an arc of spectral colours.

• Atmospheric 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 air-borne water droplets can produce a rainbow.
• An atmospheric rainbow is formed from countless individual droplets each of which reflects and refracts a tiny coloured image of the Sun towards the observer.
• As white light passes through water droplets, refraction causes the light to disperse and separate into the different colours seen by an observer.
• If the sun is behind an observer then the rainbow will appear in front of them.
• When a rainbow is produced by sunlight, the angles between the sun, each droplet and the observer determine which ones will form part of the rainbow, the colour each droplet will produce and the sequence in which they appear.

The spectral colour model represents the range of pure colours that correspond to specific wavelengths of visible light. These colours are called spectral colours because they are not created by mixing other colours but are produced by a single wavelength of light. This model is important because it directly reflects how human vision perceives light that comes from natural sources, like sunlight, which contains a range of wavelengths.

• The spectral colour model is typically represented as a continuous strip, with red at one end (longest wavelength) and violet at the other (shortest wavelength).
• Wavelengths and Colour Perception: In the spectral colour model, each wavelength corresponds to a distinct colour, ranging from red (with the longest wavelength, around 700 nanometres) to violet (with the shortest wavelength, around 400 nanometres). The human eye perceives these colours as pure because they are not the result of mixing other wavelengths.
• Pure Colours: Spectral colours are considered “pure” because they are made up of only one wavelength. This is in contrast to colours produced by mixing light (like in the RGB colour model) or pigments (in the CMY model), where a combination of wavelengths leads to different colours.
• Applications: The spectral colour model is useful in understanding natural light phenomena like rainbows, where each visible colour represents a different part of the light spectrum. It is also applied in fields like optics to describe how the eye responds to light in a precise, measurable way.