All The Colors Of The Rainbow

Rainbows are one of the great visual wonders of our colorful world. They are very familiar to most, but because of the particular conditions in which they form, it is rare to catch a glimpse of their vivid colors, and even harder to capture one on film.

Here is a collection of impressive rainbow photos, and a little information about how they form and the different variations that can be seen.

Rainbows

Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind at a low altitude angle. The most spectacular rainbow displays happen when half of the sky is still dark with raining clouds and the observer is at a spot with clear sky in the direction of the Sun. The result is a luminous rainbow that contrasts with the darkened background, it might even be possible to see a  second arc with an inverse order of colors.

The-Calm-After-the-Storm-by
ToniVC

A rainbow spans a continuous spectrum of colours; the discrete bands are an artefact of human colour vision. The most commonly cited and remembered sequence, in English, is Newton’s sevenfold red, orange, yellow, green, blue, indigo and violet (popularly memorized by mnemonics like Roy G. Biv). Rainbows can be caused by other forms of water than rain, including mist, spray, and dew.

At good visibility conditions (for example, a dark cloud behind the rainbow), the second arc can be seen, with inverse order of colours. At the background of the blue sky, the second arc is barely visible.

From an airplane it is possible to see the entire circle of a rainbow.

Moon-in-Double-Rainbow---Al
openthreads

How Rainbows Form

The light is first refracted as it enters the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40°–42°. The angle is independent of the size of the drop, but does depend on its refractive index.

The amount by which light is refracted depends upon its wavelength, and hence its colour. Blue light (shorter wavelength) is refracted at a greater angle than red light, but due to the reflection of light rays from the back of the droplet, the blue light emerges from the droplet at a smaller angle to the original incident white light ray than the red light. You may then think it is strange that the pattern of colours in a rainbow has red on the outside of the arc and blue on the inside. However, when we examine this issue more closely, we realise that if the red light from one droplet is seen by an observer, then the blue light from that droplet will not be seen because it must be on a different path from the red light: a path which is not incident with the observer’s eyes. The blue light seen in this rainbow will therefore come from a different droplet, which must be below that whose red light can be observed.

Sky-Palette-by-Nicholas_T
nicholas_t

rainbow3
feffef

Where is the Rainbow?

A rainbow does not actually exist at a particular location in the sky. Its apparent position depends on the observer’s location and the position of the sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer’s eye. This light is what constitutes the rainbow for that observer. The position of a rainbow in the sky is always in the opposite direction of the Sun with respect to the observer, and the interior is always slightly brighter than the exterior. The bow is centred on the shadow of the observer’s head, or more exactly at the antisolar point (which is below the horizon during the daytime), appearing at an angle of 40°–42° to the line between the observer’s head and its shadow. As a result, if the Sun is higher than 42°, then the rainbow is below the horizon and cannot be seen as there are not usually sufficient raindrops between the horizon (that is: eye height) and the ground, to contribute. Exceptions occur when the observer is high above the ground, for example in an aeroplane (see above), on top of a mountain, or above a waterfall.

rainbow2
eirasi

Rainbow Variations

Double Rainbow
Frequently, a dim secondary rainbow is seen outside the primary bow. Secondary rainbows are caused by a double reflection of sunlight inside the raindrops, and appear at an angle of 50°–53°. As a result of the second reflection, the colours of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The dark area of unlit sky lying between the primary and secondary bows is called Alexander’s band, after Alexander of Aphrodisias who first described it.

Double-Rainbow-Post-storm,-
carnivillain

Tertiary (Third) Rainbow
A third, or tertiary, rainbow can be seen on rare occasions, and a few observers have reported seeing quadruple rainbows in which a dim outermost arc had a rippling and pulsating appearance. These rainbows would appear on the same side of the sky as the Sun, making them hard to spot. One type of tertiary rainbow carries with it the appearance of a secondary rainbow immediately outside the primary bow. The closely spaced outer bow has been observed to form dynamically at the same time that the outermost (tertiary) rainbow disappears. During this change, the two remaining rainbows have been observed to merge into a band of white light with a blue inner and red outer band. This particular form of doubled rainbow is not like the classic double rainbow due to both spacing of the two bows and that the two bows share identical normal colour positioning before merging. With both bows, the inner colour is blue and the outer colour is red.

Double-Supernumerary-RainboProggie

Supernumerary Rainbow
A supernumerary rainbow is an infrequent phenomenon, consisting of several faint rainbows on the inner side of the primary rainbow, and very rarely also outside the secondary rainbow. Supernumerary rainbows are slightly detached and have pastel colour bands that do not fit the usual pattern.

Reflection Rainbow
When sunlight reflects off a body of water before reaching the raindrops, it may produce a reflection rainbow, if the water body is large, and quiet over its entire surface, and close to the rain curtain. The reflection rainbow appears above the horizon. It intersects the normal rainbow at the horizon, and its arc reaches higher in the sky. Due to the combination of requirements, a reflection rainbow is rarely visible. Six (or even eight) bows may be distinguished if the reflection of the reflection bow, and the secondary bow with its reflections happen to appear simultaneously.

a-rare-circumhorizon-arc-by
carplips

Circumhorizontal Arc
The circumhorizontal arc is sometimes referred to by the misnomer ‘fire rainbow’. As it originates in ice crystals it is not a rainbow but a halo.

Moonbow
moonbow (lunar rainbow, lunar bow or white rainbow) is a rainbow produced by light reflected off the surface of the moon rather than from direct sunlight. Moonbows are relatively faint, due to the smaller amount of light reflected from the surface of the Moon. They are always in the opposite part of the sky from the moon.

Few places in the world frequently feature this phenomenon. Cumberland Falls, near Williamsburg, Kentucky, U.S.A. and Victoria Falls on the border between Zambia and Zimbabwe are widely known for moonbow occurrence. Also Durham, North Carolina.

More Rainbows

rainbow-sunset-by-foreverso
foreversouls

The-Great-Gig-In-The-Sky-by
Richard0

Rainbow-Over-Route-66---Alb
openthreads

Pot-of-gold-by-Bill-Strong
bstrong

Rainbow-over-Helsinki-by-ta
taivasalla

Nature-vs-Construction-by-A
cmbellman

heather-by-10-Ninjas-Steve
steverideout

gold-by-Steve-took-it
stevewall

Doublet-by-jurvetson
jurvetson

beauty-by-pM
xiaosa

At-the-Mirth-by-Kansas-Poet
kansasphoto

3735029135_7ce06fb5a7_b
Vali…

3081828316_9e6fe787cc_o
_Massimo_

2947048555_910d7e4a24_b
AtilaTheHun

2481773708_3a72d01b70_o
David Paul Ohmer

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wili_hybrid

10476729_61b4ce6553_b
PhillipC

Text adapted from wikipedia/rainbow

Author: evad
David Sommers has been loving color as COLOURlovers' Blog Editor-in-Chief for the past two years. When he's not neck deep in a rainbow he's loving other things with The Post Family (http://thepostfamily.com/), a Chicago-based art blog, artist collective & gallery.