Starship Asterisk*

by **Chris Peterson** » Mon Sep 17, 2007 3:13 pm

bystander wrote:Bodies of water are not necessary for a triple rainbow. I have observed the phenomenom in the desert of Arizona on Hwy 89 between Tuba City and Paige.

No, but each rainbow needs a light source behind the observer and in line with its center. Usually there's only one source, the Sun, so to have multiple displaced rainbows you need something to displace the Sun's light. Usually that's a flat body of water.

Note also that you don't normally see more than half a rainbow. One exception is if you are in an airplane or on a mountain, and able to look down on it. Another exception is what you see in this case, where the Sun is reflecting from the water and therefore appears as if it were below the horizon.

by **bystander** » Mon Sep 17, 2007 1:21 pm

Bodies of water are not necessary for a triple rainbow. I have observed the phenomenom in the desert of Arizona on Hwy 89 between Tuba City and Paige.

by **auroradude** » Sat Sep 15, 2007 7:24 pm

A few years back I witnessed a similar "complex" rainbow from near Homer, Alaska. It was a double with a third rising vertically between the primary and secondary and a very faint fourth rising vertically from the secondary. It was the same configuration as seen in this image but without the reflecting pool in the foreground.
At the time, I surmised that the additional rainbows had to be caused by the sunlight reflecting off water. In this case the only body of water was Cook Inlet which is a large body of water about 80 to 150 kilometers wide in the direction of the sun. I was on a ridge with the near shore behind me by at least 2 kilometers and below by about 300 meters.
This makes it very probable that the sun was indeed reflected off another body of water located behind the observer.
-Dennis A.

by **rodir** » Fri Sep 14, 2007 7:28 am

It's not unreasonable that the lake could be of substantial size and the little water visible in the picture is only a small portion of the lake.

Indeed - the "lake" is actually no lake at all... The band of brown seaweed along the water's edge is a clear indication that this picture was taken by a fjord or even the open sea (some time other than at high tide), so there is definitely a high probability that the sun would have more than ample space to provide the needed reflections.

Now, whether it's near Trondheim or not, I couldn't tell, but it sure rains enough around here for that to be very possible...

Roar Larsen,
Trondheim, Norway

by **Chris Peterson** » Thu Sep 13, 2007 9:24 pm

Roger Tobari wrote:I once saw an amazing atmospheric display of sun halos while skiing at Alta one sunny day. I realize this phenomena has to do with ice crystals in the air lined up in a certain way, but the patterns looked similar in that there were reverse arcs among other bizarre rainbow patterns. Could there have been some ice crystals among the rain drops to explain the "halo-like" intermediate rainbows?

There's no need to involve ice crystals. The four rainbows in the image are exactly where they ought to be if their source is the Sun and a reflection of the Sun.

by **Roger Tobari** » Thu Sep 13, 2007 8:41 pm

I once saw an amazing atmospheric display of sun halos while skiing at Alta one sunny day. I realize this phenomena has to do with ice crystals in the air lined up in a certain way, but the patterns looked similar in that there were reverse arcs among other bizarre rainbow patterns. Could there have been some ice crystals among the rain drops to explain the "halo-like" intermediate rainbows?

by **GGaskill** » Thu Sep 13, 2007 7:45 pm

It's not unreasonable that the lake could be of substantial size and the little water visible in the picture is only a small portion of the lake. The visible water looks dark because it is reflecting the sky in the background. Direct illumination would have little affect unless the lake's surface was covered with something that would scatter the light, such as dust, leaves, etc.

by **adrianxw** » Thu Sep 13, 2007 5:57 am

Without doubt, a fine picture, but the "Astronomy" link is a bit thin.

by **Chris Peterson** » Thu Sep 13, 2007 4:08 am

MartinB wrote:My point is that it is impossible for the visible lake in the left front to be the source, as it is not in line. Lets ask the photgrapher to turn around, so we can see the lake behind him.

That's true. But the lake to the left of the camera is where the reflection is coming from (the Sun is behind and to the left of the camera). The actual area of reflection could either be in front of the camera (but out of the FOV), or behind it- somewhere over to the left.

Also it a coincidence that the two primaries intersect at the horizon.

No. The primaries (and secondaries) have to intersect at the horizon if they share a common mirrored source.

by **MartinB** » Thu Sep 13, 2007 2:41 am

My point is that it is impossible for the visible lake in the left front to be the source, as it is not in line. Lets ask the photgrapher to turn around, so we can see the lake behind him.

Also it a coincidence that the two primaries intersect at the horizon.

by **Chris Peterson** » Thu Sep 13, 2007 2:34 am

MartinB wrote:I think the second set of rainbows is caused by reflection off part of the lake behind the camera. This must be the case, as rainbows can only be observed when in-line with the light rays. As we can assume that the reflecting surface of the lake is horizontal, the only surfaces which can be canditates must be either in front of or behind the camera. My vote is behind.

Here's a bit of simple analysis of the picture. There are two primary rainbows and two secondary rainbows. The two primaries intersect at the horizon, have the same size (~42°), and their centers lie on a vertical line. Likewise for the two secondaries (~52°). You can scale these in Photoshop or the like and see that the numbers make sense. Next, consider the angles between the horizon and the tangents to the two primaries. I get about 67° for the "normal" rainbow, and 105° for the odd one. With that, the location of the source can be solved for: 16° above the horizon for the normal rainbow, and 16° below the horizon for the odd one. In other words, exactly what you would expect if the Sun were the direct source for the first rainbow, and a reflection from a surface parallel to the ground were the source for the second.

Assuming the image was made near Trondheim, Norway, in the last few days, that would mean it was taken at about 5:20 pm local time, with the camera pointing NNE (~28° azimuth).

The reflection could be behind the camera or in front. It does look like the lake in the foreground is in shadow, but that could be an illusion because of the dark sky in that direction. Hard to know for sure.

by **MartinB** » Thu Sep 13, 2007 12:31 am

I think the second set of rainbows is caused by reflection off part of the lake behind the camera. This must be the case, as rainbows can only be observed when in-line with the light rays. As we can assume that the reflecting surface of the lake is horizontal, the only surfaces which can be canditates must be either in front of or behind the camera. My vote is behind.

by **Lasse H** » Wed Sep 12, 2007 9:37 pm

I don't think I buy the explanation: "This rainbow is likely caused by sunlight that has first reflected off the lake before striking the distant raindrops that is reflecting sunlight back toward the observer."
The part of the lake that we see seems to be in shadow, so how could it reflect the sunlight?
Maybe there is another lake to the right of the hill that would be sunlit, but it doesn't look likely.

by **BMAONE23** » Wed Sep 12, 2007 7:27 pm

Well I did notice that the third Rainbow does seem to linE up in a continued arc with the reflected rainbow in the water.

by **GGaskill** » Wed Sep 12, 2007 6:00 pm

It should be possible to determine the path of the light causing the odd rainbows by finding their centers and using the known angles of refelction/refraction of raindrops.

by **geckzilla** » Wed Sep 12, 2007 3:28 pm

Haha, I want to believe it is there too, but I dunno, I was cautious in thinking maybe I was wishing it into existence. I mean, I see this very noisy rainbow in the best attempt but I couldn't rule out that it was just me wanting it to be there.

http://www.geckzilla.com/apod/multirainbow2.jpg

by **Howard Tayler** » Wed Sep 12, 2007 2:47 pm

Nice work with the color channels, there!

The eighth bow (a reflection of the fourth, which you've brought out nicely) is faint enough that the argument can be made that I'm not seeing it at all, but merely wishing it into existence by virtue of everything else having a reflection in the lake. But I'm going to stand by my count of eight, because I've tried to NOT see it, and it's still there.

by **geckzilla** » Wed Sep 12, 2007 2:03 pm

I have also registered just for this particular photograph. Hello.

At first I thought I may have been imagining the fourth rainbow on the left, or maybe it was some odd cloud or rainfall. So I took a portion of the area suspected of having the rainbow and equalized each of the color channels to bring out the colors existing in the area.

http://www.geckzilla.com/apod/multirainbow.jpg

The cyan, yellow, and magenta bands are quite clear to me now and I believe the fourth rainbow really is there. Logically, it would seem that there would also be an even fainter rainbow reflected directly below. However, my attempts to bring out the bands of color have failed. I am guessing that there was a reflection but the camera was unable to perceive the extremely faint colors.

But there could still be 8 rainbows. Does the thin, faint one attached to the bottom of the center area of the right-most rainbow count?

by **JohnD** » Wed Sep 12, 2007 12:20 pm

I've seen a 'reflected' rainbow, without it's primary.
The bow was diffuse and distorted, but distinct.
It looked as if the moor beyond was smeared with colour.

Such reflected bows could be termed 'virtual' as, like an ordinary bow, they are centered on an antisolar point, and are 42 degrees from that. The reflected bow appears to come from a reflected or virtual sun. See: http://www.eo.ucar.edu/rainbows/

My distorted bow was so because the loch that was reflecting the sun was smooth, but rippled. The sun, if I could have seen it reflected in the water, would have been distorted too. And the rain was not in a position to form a proper bow, so I only saw trhe virtual one.

John

by **Andy Wade** » Wed Sep 12, 2007 7:31 am

skelley wrote:I count 8, a faint one on the far left....posted using bugmenot account

Me too, I was just reading this to see if anyone else had noticed there are eight and it seems everyone has.

by **Roger Tobari** » Wed Sep 12, 2007 5:15 am

I agree.... A secondary intermediate image. This observation was enough to motivate me to register to this BB.

by **Howard Tayler** » Wed Sep 12, 2007 4:46 am

Same here. I thought, when reading the caption at first, that they must mean six ABOVE the surface of the water.

I count eight. There's a secondary, color-reversed rainbow outside the "intermediate" one, and both are reflected in the water.

by **skelley** » Wed Sep 12, 2007 4:09 am

I count 8, a faint one on the far left....posted using bugmenot account

Starship Asterisk*

Six Rainbows Across Norway... (APOD 12 Sep 2007)

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Six Rainbows

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Six Rainbows Across Norway... (APOD 12 Sep 2007)