Town Center
Double Rainbow PDF Print E-mail

What causes double rainbows? Why is the order of the colors reversed?

January 8, 2008


Double Rainbow Kleskun Springs Valley
Double Rainbow,  Kleskun Springs Valley,  Sexsmith AB
While on vacation recently our family saw a double rainbow. How do these occur? Why did the second faint rainbow (which was on top of the first) have the opposite color sequence?


Ah, rainbows – those will-o'-the-wisps of ethereal beauty, made possible only by a full lineup of optics phenomena. Let's run down the list:

1. Refraction. When a ray of sunlight strikes a raindrop, the ray refracts, or bends, at the point where it passes out of the air and into the water of the drop. The angle of the bend is determined by (a) the intrinsic light-transmitting properties of air and water (every transparent substance has its own individual index of refraction) and (b) the angle at which the ray strikes the surface of the spherical droplet – whether, e.g., it hits the drop squarely or strikes a glancing blow off to one side.

2. Dispersion. Meanwhile, the drop is acting as a prism, splitting the white light of the ray into its component colors by refracting the different wavelengths at different angles: red wavelengths bend a certain amount, orange wavelengths a slightly different amount, and so on.

3. Internal reflection. Most of the light striking the raindrop passes straight through it and out the far side, but some of it reflects off the rear interior surface of the drop and is sent in some new direction. The ratio of light transmitted to light reflected is, once again, a function of the angle at which the ray hits the surface.

4. Refraction and dispersion, part 2. When the reflected light exits the drop and re-enters the air, it's refracted and dispersed a second time.

Light rays emitted by the sun are effectively parallel when they reach the earth, and raindrops are effectively all the same shape. So when sunlight shines into a sky full of raindrops, it's encountering millions of tiny, very similar spherical prisms and interacting with each in pretty much the same way: each produces a basically identical pattern of refracted, dispersed, reflected, and re-refracted light in a spectrum of colors. The reflected red light is at its greatest intensity at an angle of 42 degrees from the direction of the sun's rays, while the violet light has maximum intensity at 40 degrees. When you face a rainy sky with the sun at your back you see a ring of red light, forming the outer edge of the rainbow, at 42 degrees from the direction of the sunlight, a violet ring at 40 degrees forming its inner edge, and all the other colors of the spectrum in between. The rainbow is entirely an optical illusion; it changes its apparent position in the sky as you change your vantage point, meaning that no two people are ever seeing a rainbow the same way (and explaining why that pot of gold is so elusive). Also, because the light forming the rainbow is reflected at angles of 40 to 42 degrees, for the most part rainbows are seen only during the hours around sunrise and sunset: if the sun is higher than 42 degrees in the sky the rainbow reflected by the raindrops will be below the horizon for an observer at ground level. You get better viewing at greater altitude, and it's possible to see complete circular rainbows from an airplane.

Now, about double rainbows: What's happening here is that the ray of sunlight bounces twice off the back interior surface of the raindrop before re-emerging into the air. The second reflection inverts the order of the colors – the secondary violet band forms at 54 degrees, the red band at 50.5 degrees – so the secondary rainbow appears above the primary one, with red on the inner edge and violet on the outer. Because the twice-reflected light has had two chances to be transmitted out the back of the raindrop rather than reflected back toward the observer, the secondary bow is much fainter than the primary and frequently cannot be seen at all; it's typical for a secondary rainbow to be visible only at certain points along the arc.

If the light is strong enough to remain visible after being reflected three times inside the raindrop, an even fainter tertiary rainbow can sometimes be seen (at least in part) above the secondary one, with the red back on the outside and the violet on the inside. And rumor has it that it's occasionally possible to see a quadruple rainbow.

Nitpickers will ask: What about diffraction? Doesn't it play a role here too? All I have to say is (a) yes, diffraction – a quantum phenomenon where light waves cancel each other out or amplify one another – sometimes figures in rainbow formation, if the raindrops are small enough, in which case (b) all bets are off – you might get smaller rainbows inside the main bow, you might get rainbows with the red in the middle – but (c) no way am I going to work out the math for this. If you're desperate to know this kind of stuff, well, that's why they invented physics grad programs.


Eugene Hecht and Alfred Zajac, Optics, Addison-Wesley Publishing Company, 1974.

Frances W. Sears, Mark W. Zemansky, and Hugh D. Young, College Physics, Fourth Edition, Addison-Wesley Publishing Company, 1974.

Local Advantages PDF Print E-mail
   Shop Local Advantages   

100 Mile Mall PDF Print E-mail
My title page contents

Welcome to the neighborhood !!


100 Mile Mall logo

What is 100 Mile Mall?

 100 Mile Mall is a social community for folks that enjoy buying local products and services, plus a large number of tools to help connect local shops with the community. Shop local and enjoy yourself, while meeting others who enjoy it too.

Why should I join? 

 There are many reasons to join, but some of the best reasons include:

  • 100% Free lifetime memberships for regular users.
  • Collect and save coupons from your local shops.
  • Discuss relevant topics that interest you.
  • Create an extensive custom profile.
  • Keep up to date on the newest Events and News.

What else can I do here? 

 Some of the more advanced users will take advantage of the custom user Websites. These are websites within that is all yours. Think of this as your own custom storefront inside of the 100 Mile Mall.

How can 100 Mile Mall help my business? 

If you are a business, you will love the features here for you. They include:

  • List your business in the directory with a full business profile with map.
  • Add all your coupons to 100 Mile Mall, you're in full control.
  • Adding unlimited user Website pages, you're in full control.
  • Optional custom built user Website themes.
  • Connect with the entire 100 Mile Mall community.


First time visitor? "Check out the helpful links below."

 First Time Visitor
 Take a  Tour
  Video Tour 
 Take a Tour
Registration Neighbor Newsflash
 Flash and Cash
 100 Mile Mall Blog.


"Update your Profile, Website and Promotions, 24/7"

What's next? 

Simple. Join the 100 Mile Mall network now! 

     or, take a look at our Demo Area. 


Young Movement PDF Print E-mail
A Young Movement  
is gathering momentum as both farmers and consumers demand a better food system and an alternative to the global food chain.
Farmers seek innovations to survive on the farm and consumers are going out of their way to support local farmers, food system and an alternative to the global food chain. (Green and Hilchey, 2002) 
Boosting Health With Local Food

Eating locally farmed food burns less fuel, but is it better for you?
The local food movement typically has been about improving the health of the planet.

Buying locally means less fuel burned to transport food, which means less pollution.
But now researchers are trying to find out if eating locally farmed food, is also better for your health.

A team of researchers at the University of North Carolina at Chapel Hill has received a grant to study the public health impact of moving toward a local, sustainable food system. An increasingly vocal local food movement calls for consumers to try to buy and eat foods produced within 100 miles of their homes.So far, there's not real evidence that eating locally farmed food is better for you. But there are many reasons to think it might be. (Read More on why local foods are healthier for you in The Visible Woman ) By definition, locally farmed food is not going to come from large commercial food companies, so people who eat locally aren't going to consume as much processed food, which typically contains lots of refined carbohydrates, sugar, fat and preservatives
Local Food Systems......better for your health
Web 2.0 Advertising PDF Print E-mail
 Web 2.0 and the End of Advertising

The idea that software on the Web is going to be largely funded by advertising is just so wrong-headed, I hardly know where to start. It had me spluttering in the latest Woman chasing dollar signBriefingsDirect Insights analyst podcastadvertising’s epitaph way back in March 2006: “Why build an economy around Attention, when Intention is where the money comes from? hosted by Dana Gardner — more on that in a moment. Let’s move on from 1.0 notions of the Web as just a publishing medium, with ads on the side. Doc Searls already pronounced what I consider to be ”

 Instead of competing to grab attention, the way to sell on the Web is to align your selling proposition with buying intention. The Web makes that easy, because it’s a platform for software automation. So use software to build automation that brings buyers and sellers together on the Web. Not just as a broker that matches deals with no added value, but by putting relevant sellers conveniently at hand at the moment when a buyer is ready to buy, making the discovery and transaction process a smoother, better, cheaper experience for all concerned. I’ll expand below on some examples of how that might happen, but here’s how I summed it up in the podcast (quoting from the transcript): 

All consumers get a Free Memberhsip
they can start to Connect  in their own local community

 “… Join for FREE"

Site Map