<p><a href="https://en.wikipedia.org/wiki/Rainbow" rel="nofollow noreferrer">Rainbows</a> are created under certain light conditions when water droplets in the atmosphere act like a <a href="https://en.wikipedia.org/wiki/Prism" rel="nofollow noreferrer">prism</a> and refract sunlight.</p>

<p>Light is part of the <a href="https://en.wikipedia.org/wiki/Electromagnetic_spectrum" rel="nofollow noreferrer">electromagnetic spectrum</a> which covers electromagnetic waves from radio waves with a wavelength of 1000 m (long wavelengths) to gamma rays with wavelengths around 0.01 nm (short wavelengths).</p>

<p>Sunlight is composed largely of all the colors of the spectrum of visible light. When our eyes see all the colors at once, our brain interprets the color as being "white light".</p>

<p>When humans see a red object that object reflects red light by absorbs all the other colors of light.</p>

<p>In the spectrum of visible light, red light has the longest wavelength of 700 nm and violet light has the shortest wavelength of 400 nm.</p>

<p>When light enters a water droplet in the atmosphere the water droplet acts like a mini prism. The angle at which the different wavelengths of light exit the prism is determined by <a href="https://en.wikipedia.org/wiki/Snell%27s_law" rel="nofollow noreferrer">Snell's Law</a> and this is why light that exist a prism, or is in a rainbow, is layered into colors with red being the first layer and violet the last.</p>

CC BY-SA 4.0
2019-09-28T20:41:48.673Z
This does not explain why the outer edge of the (primary) is red, it could also explain why the inner edge is red.
Jan Doggen
CC BY-SA 4.0
2019-09-28T05:25:38.657Z
2019-09-28T05:25:38.657Z
Fred
<p>Why is the outer color of a rainbow red?</p>

<p><a href="https://i.sstatic.net/NlMTs.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/NlMTs.jpg" alt="enter image description here"></a><br />
<sup>(Source: Wikipedia)</sup></p>

CC BY-SA 4.0
2019-09-28T14:12:00.747Z
What do you mean,"first"? It's actually the **last**!
Spencer
CC BY-SA 4.0
2019-09-28T16:57:03.477Z
https://sciencing.com/colors-rainbow-8388948.html
trond hansen
CC BY-SA 4.0
2019-09-28T18:42:16.113Z
@JanDoggen Nice try, but look at the other rainbow of the double in the picture... ;)
Spencer
CC BY-SA 4.0
2019-09-28T20:40:25.247Z
@spencer That's good for a follow up question ;-)
Jan Doggen
CC BY-SA 4.0
2019-09-30T14:08:48.887Z
Better fit for the physics stack. short answer it is a prism and lensing effect.
John
CC BY-SA 4.0
2019-10-01T15:20:58.120Z
How is this off topic? Surely atmospheric physics are earth science?
Semidiurnal Simon
<meteorology>
Why is the outer color of a rainbow red?
Mina Ahn
# Why is the outer color of a rainbow red?

(Asked by: username_0 on 2019-09-28)

Why is the outer color of a rainbow red?

[![enter image description here](https://i.sstatic.net/NlMTs.jpg)](https://i.sstatic.net/NlMTs.jpg)  
(Source: Wikipedia)

**Tags:** meteorology

> **Comments:**
> **username_1**: What do you mean,"first"? It's actually the **last**!  
> **username_2**: https://sciencing.com/colors-rainbow-8388948.html  
> **username_1**: @username_3 Nice try, but look at the other rainbow of the double in the picture... ;)  
> **username_3**: @username_1 That's good for a follow up question ;-)  
> **username_4**: Better fit for the physics stack. short answer it is a prism and lensing effect.  
> **username_5**: How is this off topic? Surely atmospheric physics are earth science?  

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## 1 answers

### Answer by username_6 on 2019-09-28. Score: 1

[Rainbows](https://en.wikipedia.org/wiki/Rainbow) are created under certain light conditions when water droplets in the atmosphere act like a [prism](https://en.wikipedia.org/wiki/Prism) and refract sunlight.

Light is part of the [electromagnetic spectrum](https://en.wikipedia.org/wiki/Electromagnetic_spectrum) which covers electromagnetic waves from radio waves with a wavelength of 1000 m (long wavelengths) to gamma rays with wavelengths around 0.01 nm (short wavelengths).

Sunlight is composed largely of all the colors of the spectrum of visible light. When our eyes see all the colors at once, our brain interprets the color as being "white light".

When humans see a red object that object reflects red light by absorbs all the other colors of light.

In the spectrum of visible light, red light has the longest wavelength of 700 nm and violet light has the shortest wavelength of 400 nm.

When light enters a water droplet in the atmosphere the water droplet acts like a mini prism. The angle at which the different wavelengths of light exit the prism is determined by [Snell's Law](https://en.wikipedia.org/wiki/Snell%27s_law) and this is why light that exist a prism, or is in a rainbow, is layered into colors with red being the first layer and violet the last.

> **Comments:**
> **username_3**: This does not explain why the outer edge of the (primary) is red, it could also explain why the inner edge is red.  

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