APOD: Rainbow at Sunset (2010 Aug 07)

[APOD Robot]

Rainbow at Sunset

Explanation: Where is the Sun when you see a rainbow? Behind you, of course. But you can see both a rainbow and the Sun (far right) side by side in this graceful panorama recorded on July 28. The cloudy sunset view covers a full 360 degrees around the horizon, composed using 20 individual images taken from an observatory on the outskirts of Potsdam, Germany. The rainbow itself is produced by sunlight internally reflected in rain drops from the direction opposite the Sun back toward the observer. As the sunlight passes through the drops, from air to water and back to air again, longer wavelengths (redder colors) are refracted or bent less than shorter wavelengths (bluer colors), separating the sunlight into the colors of the rainbow. This sharp picture captures the full, bright, primary rainbow arc as well as more subtle effects. You can see a partial, dimmer, secondary rainbow arc above and left of the primary, and faint arcs just inside the primary rainbow called supernumerary rainbows.

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[Hugh Manatee]

WHOAH! A full on rainbow!

[neufer]

[img3="The Orangerieschloss in Sanssouci ("Without Worries") Park, Potsdam"]http://upload.wikimedia.org/wikipedia/c ... ngerie.jpg[/img3][img3="The Sanssouci ("Without Worries") Palace, Potsdam"]http://upload.wikimedia.org/wikipedia/c ... ssouci.jpg[/img3]

[img3="The Neues Palais in Sanssouci ("Without Worries") Park, Potsdam"]http://upload.wikimedia.org/wikipedia/c ... Palais.JPG[/img3]


http://asterisk.apod.com/vie ... am#p107561


http://asterisk.apod.com/vie ... am#p114357

[geckzilla]

Rainbow dude would be impressed.

[Brem]

Whenever I see a rainbow I think of Walter Lewin's video lectures:

http://ocw.mit.edu/courses/physics/8-03 ... es/embed2/

[orin stepanek]

Thanks APOD; I don't recall seeing a rainbow at Sunset before! Maybe an hour before Sunset. I love the large arc in this view. I have seen as many as three rainbows the third being quite faint.

[hungrybear]

OMG it's a full rainbow, all the way.

It's so intense...

What does it mean?

[biddie67]

I'm envious of that marvelous 360 degree view - where I live, I only get to see smaller pieces of rainbows - great photo!!

[Beyond]

OMG it's a full rainbow, all the way.

It's so intense...

What does it mean?

According to the story -- it means the whole Earth will never be flooded with water again. But that does not include just parts of the Earth, so keep your water wings handy

[drollere]

one aspect of the rainbow geometry: for each rainbow observer, the center of the circle implied by the rainbow arc is always at the solar shadow of the observation point, which in this case appears to be the top of the observation dome shadow cast on the ground, just below the wall of the small white house. (in normal circumstances, it is the shadow of your head.) the distance of this antisolar point below the horizon under the rainbow is always equal to the distance of the sun above the horizon. but this is the *true* or abstract horizon, not the physical horizon obscured by random objects and topography. there is also typically a darkening of the sky visible between the primary and secondary rainbows, called "Alexander's dark band", and a lightening of the sky underneath the primary rainbow, which includes the supernumerary bows.

[jman]

What does it mean?

Actually, it means you've eaten way too many mushrooms, dude.

[Boomer12k]

That would be TWO POTS OF GOLD, RIGHT????????

[bystander]

What does it mean?

The sun is shining and there are water droplets in the air.

[Beyond]

What does it mean?

The sun is shining and there are water droplets in the air.

That makes me think of a question. How can sunlight shine through all those individual water drops and yet display as one (or more) indivdual rainbow(s)?

[carapils]

Double rainbow, all the way 'cross the sky. Yeah, so intense.
Double rainbow, all the way 'cross the sky. Oh my oh my god, look at that rainbow!

http://www.youtube.com/watch?v=MX0D4oZwCsA

[Ann]

That's a great image, and it becomes even better by its 360 degrees perspective.

Ann

[neufer]

How can sunlight shine through all those individual water drops and yet display as one (or more) indivdual rainbow(s)?

If you look very closely at the image you can distinguish each one of those individual water drops.
Each has a distinct color.

[Beyond]

How can sunlight shine through all those individual water drops and yet display as one (or more) indivdual rainbow(s)?

If you look very closely at the image you can distinguish each one of those individual water drops.
Each has a distinct color.

If i had seen your face when you posted this response, i am sure that i would have seen a large lump on one side of your face from being filled with all that tounge.
I do not think i have ever heard any type of explanation of a rainbow. After posting my question, it dawned on me that the explanation, scientificly speaking, could only have something to do with the photon effect where the photons are not acting normally, but are acting as a group to separate and display an arc for each individual color.
If it wasn't for that effect, all that may happen is a sort of colorful sky or maybe nothing at all that would be visible to us and there would be less of a choice of Apod pictures available.
So if I'm right - lets hear it for the photons -- YEA! RAH RAH YAHOO!!

[bob.altizer@basysconsulting.com]

What a fabulous coincidence on APOD! My wife and I saw one of these just last night (Friday, August 6) in Ahwatukee, Arizona after a brief misting rain at sunset. It lasted only about 5 minutes from our vantage point as the air dried and the sun set behind them mountains.

[neufer]

How can sunlight shine through all those individual water drops and yet display as one (or more) indivdual rainbow(s)?

If you look very closely at the image you can distinguish each one of those individual water drops.
Each has a distinct color.

If i had seen your face when you posted this response, i am sure that i would have seen a large lump on one side of your face from being filled with all that tongue.

I do not think i have ever heard any type of explanation of a rainbow. After posting my question, it dawned on me that the explanation, scientifically speaking, could only have something to do with the photon effect where the photons are not acting normally, but are acting as a group to separate and display an arc for each individual color.
If it wasn't for that effect, all that may happen is a sort of colorful sky or maybe nothing at all that would be visible to us and there would be less of a choice of Apod pictures available.
So if I'm right - lets hear it for the photons -- YEA! RAH RAH YAHOO!!

The basic classical understanding of rainbows long preceded any idea of photons.
(Just imagine that the screen pixels are actually spherical water droplets and things work out fine.)

René Descartes' sketch of how primary and secondary rainbows are formed

---

<<Roger Bacon, who wrote in his Opus Majus of 1268 about experiments with light shining through crystals and water droplets showing the colours of the rainbow. In addition, Bacon was the first to calculate the angular size of the rainbow. He stated that the rainbow summit can not appear higher than 42° above the horizon. Theodoric of Freiberg is known to have given an accurate theoretical explanation of both the primary and secondary rainbows in 1307. He explained the primary rainbow, noting that "when sunlight falls on individual drops of moisture, the rays undergo two refractions (upon ingress and egress) and one reflection (at the back of the drop) before transmission into the eye of the observer".] He explained the secondary rainbow through a similar analysis involving two refractions and two reflections.

Descartes' 1637 treatise, Discourse on Method, further advanced this explanation. Knowing that the size of raindrops did not appear to affect the observed rainbow, he experimented with passing rays of light through a large glass sphere filled with water. By measuring the angles that the rays emerged, he concluded that the primary bow was caused by a single internal reflection inside the raindrop and that a secondary bow could be caused by two internal reflections. He supported this conclusion with a derivation of the law of refraction (subsequently, but independently of, Snell) and correctly calculated the angles for both bows. His explanation of the colours, however, was based on a mechanical version of the traditional theory that colours were produced by a modification of white light.>>

[owlice]

The MIT OpenCourseWare lecture (at the link provided earlier) provides a very good explanation. Or look here: http://www.atoptics.co.uk/rainbows/primrays.htm

One of my favorite images is this one: http://www.atoptics.co.uk/fz63.htm

[bystander]

Or look here: http://www.atoptics.co.uk/rainbows/primrays.htm

Continued here: http://www.atoptics.co.uk/rainbows/primcone.htm

[Beyond]

The MIT OpenCourseWare lecture (at the link provided earlier) provides a very good explanation. Or look here: http://www.atoptics.co.uk/rainbows/primrays.htm

One of my favorite images is this one: http://www.atoptics.co.uk/fz63.htm

Owlice, one of your favorite images that you posted a link to reminds me more of a light yellow Sno-Ball than a rainbow. I've never seen a "filled in" one like that before.
Even with all this information flooding in about how a rainbow is made, i still think that photons have a hand in it. After all, you do need light and round drops of water to make a rainbow and photons are light particles and they do act a bit strange (to us) at times.

[Beyond]

Neufer wrote - "The basic classical understanding of rainbows long preceded any idea of photons."

Yes that is true, however, photons long preceded any idea of rainbows. Just because man hasn't become aware of something yet, does not mean that something is not at work doing what it does. So i think that photons were already at work long before any conditons were wet enough any where for light to flow through and produce a rainbow.

[neufer]

One of my favorite images is this one: http://www.atoptics.co.uk/fz63.htm

Owlice, one of your favorite images that you posted a link to reminds me more of a light yellow Sno-Ball than a rainbow. I've never seen a "filled in" one like that before.

EVERything reminds you of Sno-Balls; it is probably due to the Sno-Ball Effect.

Even with all this information flooding in about how a rainbow is made, i still think that photons have a hand in it. After all, you do need light and round drops of water to make a rainbow and photons are light particles and they do act a bit strange (to us) at times.

Photons play a secondary role by creating those diffraction effects seen around 1 O'clock in today's APOD.