Light - Reflection and Refraction


A rainbow is not a physical object but a meteorological phenomenon in the sky. It forms due to refraction, reflection, and dispersion of sunshine in water droplets resulting in a spectrum of sunshine appearing within the sky. It is seen as a beautiful multicoloured circular arc in the sky. Rainbows are often full circles. However, practically an observer usually sees only an arc formed by illuminated droplets above rock bottom and centred on a line from the sun to the observer’s eye.



Introduction to Rainbow

Usually, a primary rainbow arc shows a red colour on the outer part and violet on the inner side. In case of a double rainbow, there is a second arc that is visible outside the primary arc and has the order of its colours reversed, with red on the inner side of the arc. This is often caused by the sunshine being reflected twice on the within of the droplet before leaving it.

A rainbow does not occur at any selected distance from the observer but comes from an optical phenomenon caused by any water droplets viewed from a particular angle relative to a light-weight source. Thus, a rainbow isn’t an object and can’t be physically approached. Indeed, it’s impossible for an observer to determine a rainbow from water droplets at any angle apart from the customary one of 42 degrees from the direction opposite the sunshine source.

Rainbows span an endless spectrum of colours. Human eyes perceive rainbow as red, orange, yellow, green, blue, indigo and violet. Rainbows are often caused by many sorts of airborne water.

Number of colours during a spectrum or a rainbow

A spectrum obtained employing a glass prism and some extent source may be a continuum of wavelengths without bands. The amount of colours that the human eye during a position is ready” is in a position to differentiate in a spectrum is within the order of 100. The apparent discreteness of main colours could also be an artefact of human perception and thus the precise number of main colours may be a somewhat arbitrary choice.

Newton at first divided the rainbow into seven colours. His belief derived from the beliefs of the traditional Greek sophists, who thought there was a connection between the colours, the musical notes, the known objects within the system, and therefore the days of the week. The colour pattern of a rainbow is different from a spectrum, and therefore the colours are less saturated. there’s spectral smearing during a rainbow due to the very fact that for any particular wavelength, there’s a distribution of exit angles, instead of one unvarying angle.

Additionally, a rainbow may be a blurred version of the bow obtained from some extent source, because the disk diameter of the sun (0.5°) can’t be neglected compared to the width of a rainbow (2°). Further red of the first supplementary rainbow overlaps the violet of the primary rainbow, so instead of the ultimate colour being a variant of spectral violet, it’s actually a purple. Therefore, the amount of colours of a rainbow is variable.


When water drops are present within the air and sunlight shines from behind the observer at a low altitude angle, a rainbow is visible. This is why rainbows are usually visible within the western sky during the morning and within the eastern sky during the first evening. The best rainbow pattern is visible when half the sky remains dark with raining clouds. Therefore the observer is at a spot with clear sky within the direction of the sun.

The rainbow effect is additionally commonly visible near waterfalls or fountains. Rarely, a moonbow, lunar rainbow or nighttime rainbow, are often visible on strongly moonlit nights. It is difficult to photograph the entire semicircle of a rainbow in one frame, as this is able to require an angle of view of 84°. For a 35 mm camera, a fisheye lens with a focal distance of 19 mm or less would be required.

When sunlight encounters a raindrop, a part of the sunshine is reflected and therefore the rest enters the raindrop and refracts from the surface of the raindrop. When this light hits the rear of the raindrop, a number of it’s reflected off the rear. The overall effect is that a part of the incoming light is reflected back over the range of 0° to 42°, with the foremost intense light at 42°. This angle is independent of the dimensions of the drop but does depend upon its index of refraction. Seawater features a higher index of refraction than rainwater. Therefore the radius of a “rainbow” in the spray is smaller than a real rainbow. This is visible to the eye by a misalignment of those bows.

Furthermore, the quantity by which light is refracted depends upon its wavelength, and hence it’s colour. This effect is dispersion. As blue light is of the shorter wavelength of the spectrum, it is refracted at a greater angle than red light. But the cause of the reflection of sunshine rays from the rear of the droplet, the blue light emerges from the droplet at a smaller angle to the first incident white light ray than the red light. Due to this angle, blue is visible at the within of the arc of the first rainbow, and red on the surface.

A rainbow doesn’t exist at one particular location. Many rainbows exist. However, just one is often seen counting on the actual observer’s viewpoint as droplets of sunshine illuminated by the sun. All raindrops refract and reflect the daylight within the same way, but only the sunshine from some raindrops reaches the observer’s eye.

Types of Rainbow

Double rainbows- We see a double rainbow when both the first and secondary rainbows are visible. Secondary rainbows occur due to a double reflection of sunlight inside the water droplets.

Twinned rainbow- The very rare twinned rainbow appears as two rainbow arcs that split from a single base. The colours in the secondary bow appear in the same order as the primary rainbow.

Supernumerary rainbows: In certain circumstances, one or several narrow, faintly coloured bands are often seen bordering the violet fringe of a rainbow; i.e., inside the first bow or, much more rarely, outside the secondary. These extra bands are supernumerary rainbows.

Full-circle rainbow: In theory, every rainbow may be a circle, but from the bottom, usually only its upper half is often visible. From a high viewpoint such as a high building or an aircraft, the full circle may be visible on fulfilling all the climate conditions.

Monochrome rainbow or Red rainbow: Occasionally a shower may happen at sunrise or sunset, where the shorter wavelengths like blue and green are scattered and essentially faraway from the spectrum.

Fogbow- Fogbows form by much smaller cloud and fog droplets that diffract light extensively. It forms in the same way as rainbows. They are almost white with faint reds on the surface and blues inside.

Circumhorizontal and circumzenithal rainbow arcs- The circumzenithal and circumhorizontal arcs are optical phenomena like a rainbow but they’re not rainbows. They are members of the massive family of halos.

FAQs about Rainbow

Q.1. Can you stand inside a rainbow?

Answer- One can’t reach the end of the rainbow because a rainbow is kind of like an optical illusion. Thus it doesn’t matter however you move, the rainbow will always be the same distance away from you. Hence, no one can reach the end of a rainbow.

Q.2. How long does a rainbow last?

Answer- The highest rainbow recorded as lasting six hours, according to the Guinness World Records. Rainbows usually last a maximum of an hour, according to the Guinness website.

Q.3. How rare is a full rainbow?

Answer- Full rainbow is a very rare sight. Sky conditions need to be just perfect for a full rainbow. Even if they are, the horizon blocks the bottom part of a full-circle rainbow usually.

Share with friends

Customize your course in 30 seconds

Which class are you in?
Get ready for all-new Live Classes!
Now learn Live with India's best teachers. Join courses with the best schedule and enjoy fun and interactive classes.
Ashhar Firdausi
IIT Roorkee
Dr. Nazma Shaik
Gaurav Tiwari
Get Started

Leave a Reply

Notify of

Customize your course in 30 seconds

Which class are you in?
No thanks.