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I know how rainbows are formed, and why.

Usually it is said that the Sun must be behind the observer, in order for its light to be totally reflected inside the droplet and then reach the observer.

But surely not all the light is totally reflected?

There must be some radiation refracting from inside the droplet to the air: since different wavelengths refract through different angles, shouldn't we also see a rainbow when the Sun is in front of us?

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  • $\begingroup$ As an aside, you might be interested in hunting down a copy of Color and Light in Nature $\endgroup$ – user20936 Mar 31 '14 at 20:28
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You are right. Rainbows can occur all over the sky. However the traditional one and two internal reflections of the primary and secondary bows send light back towards the sun and hence their bows appear opposite the sun and centered on the antisolar point. The reflection of the main light makes these bows stand out.

And only the light that enters a droplet is reflected in some manner. Sometimes it is a single reflection and you get a primary rainbow which everyone is familiar with. Depending on how dense the droplets are some light will pass through all the drops and will not be reflected creating a hazy or dim rainbow.

If some of the light bounces inside the droplet (enters but does not exit and bounces inside twice more) you'll see a weaker double rain bow caused the the light that has bounced 2 times.

double

So there are many orders of rainbows:

orders

A zero order is when there are no internal droplet reflections and the droplet is sun ward. This creates an orange shifted glow.

zero

There must be some radiation refracting from inside the droplet to the air: since different wavelengths refract through different angles, shouldn't we also see a rainbow when the Sun is in front of us?

The width you see of the rainbow represents the spreading of the frequencies and their slightly different refraction angles. Light can be refracted in many different ways from the droplets with the sun in between you, but they don't form the traditional bow shape which has to do with the arc of the sun being behind you and refracted back. This is mostly because the suns brightness make it too hard to see.

And here are some other refraction examples that are not really considered rainbows.

non-rainbow

Take a look at this site for more about atmospheric optics.

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  • $\begingroup$ Ah, nice clarification. Tbh I thought a zero order would be completely unobservable with the naked eye. Am I right? Is this something you can observe with a camera/filter only? $\endgroup$ – Constandinos Damalas Mar 31 '14 at 18:49
  • $\begingroup$ No this is a type of scattering and it is caused by water droplets or other particles in the air. Like the red sunset/sunrise. $\endgroup$ – user6972 Mar 31 '14 at 18:52
  • $\begingroup$ In case one didn't take a close enough look at secondary rainbows (because they're fainter): note the inverted order of colours due to the extra refraction. $\endgroup$ – Simeon Carstens Mar 31 '14 at 21:54
  • $\begingroup$ The third and fourth order rainbows were first photographed in 2011 atoptics.co.uk/rainbows/ord34.htm and the fifth order rainbow in 2012 earthsky.org/earth/first-ever-image-of-5th-order-rainbow $\endgroup$ – Farcher Jun 16 '16 at 19:53
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Check this: You can see that the angle difference is much bigger when the light gets reflected, and can be differentiated much easier. Also another factor which probably plays a very important role is that the sun is in front of you, and its simply too strong in comparison with the light from the droplet, thus making it even more difficult to inspect this phenomenon.

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30 or 40 years ago I saw a normal looking rainbow while looking towards the sun.(although the sun was hidden behind tall City buildings it was late afternoon and I was looking towards the West). And while looking at it in utter disbelief, a second rainbow started to form, but this second rainbow was upside down, and eventually about a quarter of an upside down rainbow formed, and I thought the centre of this upside-down rainbow would have been at my Zenith.Unfortunately this was before the era when we all carried cameras in our pockets, but it definitely occurred. These two rainbows were separated they were not joined.

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    $\begingroup$ Maybe that wasn't exactly a rainbow, but a Curcumzenithal Arc $\endgroup$ – Eagle 21 hours ago
  • $\begingroup$ Eagle, I have seen that photo, and that's why I mentioned that the two rainbows I saw were not joined together, as they are in that photo. But the main reason for my post was to say that I saw a normal rainbow while looking towards the sun and that seems to be disbelieved by everybody.I remember my school physics telling me the sun was always behind me that's why I was astounded when I saw a rainbow looking towards the sun. $\endgroup$ – Michael 17 hours ago
  • $\begingroup$ The "joined rainbow" in the wikipedia photo is a supralateral arc, which doesn't always occur with a circumzenital arc. There are nice explanations and photos at Atmospheric Optics. $\endgroup$ – rob 9 hours ago

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