APOD: A Full Circle Rainbow over Australia (2014 Sep 30)

[APOD Robot]

A Full Circle Rainbow over Australia

Explanation: Have you ever seen an entire rainbow? From the ground, typically, only the top portion of a rainbow is visible because directions toward the ground have fewer raindrops. From the air, though, the entire 360 degree circle of a rainbow is more commonly visible. Pictured here, a full circle rainbow was captured over Cottesloe Beach near Perth, Australia last year by a helicopter flying between a setting sun and a downpour. An observer-dependent phenomenon primarily caused by the internal reflection of sunlight by raindrops, the 84-degree diameter rainbow followed the helicopter, intact, for about 5 kilometers. As a bonus, a second rainbow that was more faint and color-reversed was visible outside the first.

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[Thunderlips]

After all this time trying to find gold at the end of the Rainbow I discover there actually is no end.
So much wasted time...

[Ann]

That's very nice!

Of course the rainbow is really a full circle, but from the ground some of it is always below the horizon.

It's nice to see the rainbow for what it really is!

Ann

[geckzilla]

The end of the rainbow is invisible but it exists at the smallest wavelength possible in the electromagnetic spectrum. Whether that forms a point in the center or a circle of smaller dimension than the visible rainbow I don't know. So, I know there is a smallest possible wavelength. Is there a largest possible wavelength? If so, there could be two ends to a rainbow just as previously thought but they are in radically different positions.

[Nitpicker]

That's very nice!

Of course the rainbow is really a full circle, but from the ground some of it is always below the horizon.

It's nice to see the rainbow for what it really is!

Ann

With the Sun shining cloudless behind you, and sufficient water drops in front of you, the primary rainbow is centred on a full 42° cone with an apex at your eyeball and an axis in the direction of the sunlight. Such a cone appears to the eyeball as a circle, or more commonly, with insufficient drops on the low side where the ground is closer, an arc.

There is a nice picture of a full rainbow made from the ground, with a garden sprinkler, here:

Click to view full size image

http://somethingsurprising.blogspot.com ... nbows.html

[geckzilla]

Is a rainbow happening on a spherical "surface" or is it flat?

[Nitpicker]

The end of the rainbow is invisible but it exists at the smallest wavelength possible in the electromagnetic spectrum. Whether that forms a point in the center or a circle of smaller dimension than the visible rainbow I don't know. So, I know there is a smallest possible wavelength. Is there a largest possible wavelength? If so, there could be two ends to a rainbow just as previously thought but they are in radically different positions.

At some point in the spectrum, the wavelength of light becomes bigger than the water drops. This limits things at the red end I think. (I'll need more time than I have at the moment to think about the other end.)

[geckzilla]

Please find the answers to my questions. I am having a crisis of knowledge about light lately. All I can think about is how little I understand it.

[Boomer12k]

BEAUTIFUL AND AWESOME!!!!!

:---[===] *

[Boomer12k]

After all this time trying to find gold at the end of the Rainbow I discover there actually is no end.
So much wasted time...

OOOOHHHHHH.....THAT'S WHY!!!!!!!!!! Full Circle...no end....NO GOLD!!!! Shoooooot!!!!

Fooled Again.....

:---[===] *

[teal]

How do we know this rainbow effect is not caused by the helicopter window?

[Chris Peterson]

How do we know this rainbow effect is not caused by the helicopter window?

By what mechanism?

The window is not in direct sunlight, the rainbow is centered on the antisolar point and shows all the features of a normal rainbow created by water drops. And there's nothing unusual about a full circle rainbow, we're just not usually in the right place to make an image.

[Chris Peterson]

The end of the rainbow is invisible but it exists at the smallest wavelength possible in the electromagnetic spectrum. Whether that forms a point in the center or a circle of smaller dimension than the visible rainbow I don't know. So, I know there is a smallest possible wavelength. Is there a largest possible wavelength? If so, there could be two ends to a rainbow just as previously thought but they are in radically different positions.

I don't know that there's a smallest possible wavelength for EM. Possible a Planck length. And the longest would be defined by the age of the universe and the speed of light.

But if we're talking about rainbows, we aren't going to go too far beyond the visible spectrum. Much shorter and the water drops will be opaque. Longer and they'll cease to support internal light paths (and may be opaque as well).

[geckzilla]

What about an imaginary medium with similar refractive properties to a rainbow that isn't opaque to any light?

[Ron-Astro Pharmacist]

In my mind an imaginary medium is a "large" or "extra-large" depending on the manufacture. But you are usually more serious than me. How would you define an imaginary medium? Taking about a substance not yet described or ill-defined?

[geckzilla]

I meant a substance with the refractive qualities of a raindrop but without the absorptive qualities.

[Ron-Astro Pharmacist]

I should have been able to spot the typo but it did give me an idea for a new signature. I'll have to defer to a higher intellect for your question though. I have never pondered waters absorptive quality with respect to light so hopefully an answer may soon follow. Google only served to complicate the issue – in my mind.

[geckzilla]

Our perception of light is so shallow and biased that it is completely unintuitive for us to try to think of it in any way other than how our eyes and brains interpret the tiny visible slice we are alotted. A plastic box that looks utterly opaque is actually translucent just beyond our perception. A glass of water looks perfectly clear but is mercifully opaque at higher energies.

[Sinan İpek]

Have you ever watered your garden while it's raining? I have.
What I saw was this: The rainbow formed by the water coming out of the hose completely overlaps the rainbow on the sky. This was very interesting. Because, you perceive the hose-induced-rainbow as being 'small' while you perceive the sky-rainbow as being 'large'. So, when you see them overlap, it was interesting.
By the way, you also see that little rainbow completes the other's 'bow' into a complete circle.
I recommend you do this experiment by yourself. Go water the grass while it's raining.

[Philo]

Is it me, or does the area within the rainbow appear brighter than the area outside the rainbow? Is this some kind of lensing effect, or is it just brighter and dimmer, adjacent to the rainbow itself?

[Ron-Astro Pharmacist]

A glass of water looks perfectly clear but is mercifully opaque at higher energies.

I guess I just needed to get my "mind" in to the clouds to dream of a way to see water in a different light. Thanks for the insight. My cloud "hat" goes off to you.

[geckzilla]

It's funny how intuitive it is that a thick cloud is largely opaque and yet it is also water...

[Chris Peterson]

Is it me, or does the area within the rainbow appear brighter than the area outside the rainbow? Is this some kind of lensing effect, or is it just brighter and dimmer, adjacent to the rainbow itself?

That's part of the optics of rainbows. This effect is always present.

[Ron-Astro Pharmacist]

Off on another tangent, do you suppose the vanishing point should be the direct center of a full circle rainbow? The shadows of the trees seem to point further east. It's another interesting component of today's APOD.

Of course, so is the "golf" course. I'm sure that's a coincidental happenstance a few might find as a nice backdrop. To be funny – a celestial hole in one.

[Beyond]

A sense of humor is nothing to make light of.

BRILLIANT!!