Rainbow , And How To Create A Realistic Rainbow Effect With Photoshop (with video) قوس قزح

The original picture 

The Photoshop picture

What is a rainbow ?

A rainbow is an optical ( Optics is the branch of physics which involves the behavior and properties of light,) and meteorological ( Meteorology is the scientific study of the atmosphere) phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.

In a so-called "primary rainbow" (the lowest, and also normally the brightest rainbow) the arc of a rainbow shows red on the outer (or upper) part of the arc, and violet on the inner section. This rainbow is caused by light being reflected once in droplets of water. In a double rainbow, a second arc may be seen above and outside the primary arc, and has the order of its colours reversed (red faces inward toward the other rainbow, in both rainbows). This second rainbow is caused by light reflecting twice inside water droplets. The region between a double rainbow is dark. The reason for this dark band is that, while light below the primary rainbow comes from droplet reflection, and light above the upper (secondary) rainbow also comes from droplet reflection, there is no mechanism for the region between a double rainbow to show any light reflected from water drops.
Triple rainbows are impossible.

For colours seen by a normal human eye, the most commonly cited and remembered sequence, in English, is Newton's seven-fold red, orange, yellow, green, blue, indigo and violet. However, colour-blind persons will see fewer colors.

Causes And Visibility 
Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew( Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening.).
The rainbow effect is also commonly seen near waterfalls or fountains. In addition, the effect can be artificially created by dispersing water droplets into the air during a sunny day.
The rainbow effect is also commonly seen near waterfalls or fountains. In addition, the effect can be artificially created by dispersing water droplets into the air during a sunny day.

N.B A moonbow (also known as a 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.

Its Variations
* Double rainbow
* Supernumerary rainbow or stacker rainbow
* Reflected rainbow or reflection rainbow
* Monochrome rainbow
* Circumhorizontal arc

قوس قزح

قَوْسُ قُزح يسمى كذلك قوس المطر أو قوس الألوان وهو ظاهرة طبيعية فيزيائية ناتجة عن انكسار وتحلل ضوء الشمس خلال قطرة ماء المطر

يظهر القوس قزح بعد سقوط المطر أو خلال سقوط المطر والشمس مشرقة

تكون الألوان في القوس اللون الأحمر من الخارج ويتدرج إلى البرتقالي فالأصفر فالأخضر فالأزرق فأزرق غامق (نيلي) فبنفسجي من الداخل

ضوء الشمس يحتوي علي العديد من الالوان الطيفية وهي عبارة عن أشعة ذات اطوال موجية مختلفة

يظهر قوس القزح عادة بشكل نصف دائري وفي حالات نادرة يكون قمرياً حيث يكون انكسار ضوء القمر المسبب لهُ عبر قطرة الماء ملائماً مع مكان وجود القمر في تلك اللحظات. ويظهر للمشاهد نتيجة لضوئهِ الخافت أبيض لأن العين البشرية لا تستطيع ان ترى الألوان في الليل

Open the landscape picture you like in Photoshop .

• Add new layer and select the Gradient Tool , it will open the tool option bar up, select the shape like a rainbow ,and choose ,radial gradient and draw a horizontal line , it will draw the bow.Put the the blending mode of the layer to Screen . 
• Go to Filter Menu - Blur - Motion Blur put the distance to 24to 26 .   
• Add layer mask to that layer by selecting the layer and click the icon down( the diagram). Put the Foreground color to black and Background color to white .Go again to the Gradient Tool and select now black and white gradient and draw a line from down upward outside the bow .
• Duplicate the layer and put the Opacity from 10-15.
• Duplicate the second layer again and select the move tool and move it slightly outside the arc .
• Select the lower two layers and put them in one group (Ctrl +G).
• Add a layer mask to the group layer and put the color to black and select soft brush ( put the hardness to 0) and click on the area of the arc on the ground to eliminate it .
• That's all , save your work .  

Thanks