Moonbow and Rainbows Over Patagonia (APOD Aug 10th, 2009)

[MartinM]

Hi all,

Very nice animation with astonishing phenomena!

http://apod.nasa.gov/apod/ap090810.html

I haven't seen a moonbow before, although I was able to observe a moondog (like a sundog, but lit by the moon) over Munich, Germany, in February of this year.

Cheers,
Martin

[geckzilla]

My favorite part is seeing how the moonbows and rainbows (or should they be called sunbows?) move as the moon and sun set and rise.

[neufer]

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Stars, Moonbow and rainbow over Torres del Paine
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<<Torres del Paine National Park is a Chilean National Park encompassing a mountains, glacier, lake, and river-rich area in southern Chile. The Cordillera del Paine is the centerpiece of the park. It lies in a transition area between the Magellanic subpolar forests and the Patagonian Steppes. Among the lakes are the Dickson Lake, Nordenskjöld Lake, Pehoe Lake, Grey Lake, Sarmiento Lake, and Del Toro Lake. All are vividly colored, most due to rock flour suspended in their waters. The main river flowing through the park is Paine River.

Much of the geology of the Paine Massif area consists of Cretaceous sedimentary rocks that have been intruded by a Miocene-aged laccolith. Orogenic and erosional processes have shaped the present-day topography, glacial erosion being the main one responsible for the sculpturing of the massif in the last tens of thousands of years. A good example of the latter are the Cuernos del Paine, whose central bands of exposed granite strongly contrast with the dark aspect of their tops, which are remnants of a heavily eroded sedimentary stratum. In the case of Las Torres, what once was their overlying sedimentary rock layer has been completely eroded away, leaving behind the more resistant granite.>>

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<<A moonbow (also known as a lunar rainbow, lunar bow or white rainbow) is a rainbow produced by the moon rather than the sun. Moonbows are relatively faint, due to the smaller amount of light from the Moon. They are always in the opposite part of the sky from the moon. It is difficult for the human eye to discern colors in a moonbow because the light is usually too faint to excite the cone color receptors in human eyes. As a result, they often appear to be white. However, the colors in a moonbow do appear in long exposure photographs.

Moonbows are most easily viewed when the moon is near to full (when it is brightest). For other than those produced by waterfalls, the moon must be low in the sky (less than 42 degrees and preferably lower) and the sky must be dark. And of course there must be rain falling opposite the moon. This combination of requirements makes moonbows much more rare than rainbows produced by the sun.

Moonbow at the Lower Yosemite Fall

Few places in the world frequently feature this phenomenon. Cumberland Falls, near Williamsburg, Kentucky, U.S.A.; Waimea, Hawaii, U.S.A.; Trans-Ili Alatau, Kazakhstan; upper and lower Yosemite falls and Victoria Falls on the border between Zambia and Zimbabwe are widely known for moonbow occurrence.>>

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<<Mambo is a Cuban musical form and dance style. The word mambo (which means conversation with the gods) derives from ki-kongo based language, the language spoken by West-Central African slaves taken to Cuba. The history of modern mambo begins in 1938, when "Mambo" was written by Orestes and Cachao López. The song was a danzón, descended from European social dances like the English country dance, French contredanse and Spanish contradanza, but it used rhythms derived from African folk music.

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Explanation: Pictured above is a moonbow stretching over Salt Pond Bay in St. John, Virgin Islands. Sailboats are visible on the left. To bring out the moonbow, an exposure of 30 seconds was needed, making the picture appear as if it was taken during the day. Since moonlight is itself reflected sunlight, the colors are nearly the same. Both rainbows and moonbows are created by light being scattered inside small water droplets, typically from a nearby rainfall. The raindrops each act as miniature prisms, together creating the picturesque spectrum of colors seen.

http://www.dailymotion.com/video/x2p7in ... senora_fun
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[cherlin]

The page states that rainbows and moonbows are caused by drops of water behaving like prisms. That is one part of the story. The second essential part is internal reflection in the raindrops. Double rainbows are produced by single and double internal reflection.

http://en.wikipedia.org/wiki/Rainbow#Sc ... xplanation

Up to 200 rainbows produced by multiple internal reflection can be detected under laboratory conditions with powerful lasers and sensitive photodetectors. The first dozen or more are detectable using amateur equipment.

Amateur Scientist, Scientific American July 1977, page 138 - 144: How to create and observe a dozen rainbows in a single drop of water by Jearl Walker.

Further detail requires an analysis of classical lightwave interference (supernumerary bows in green and purple)

Jearl Walker, Mysteries of rainbows, notably their rare supernumerary arcs, Amateur Scientist column for Scientific American, June, 1980.

or quantum mechanics (variations not visible to the eye but detectable in the lab).

Nussenzveig, H. Moyses, "The Theory of the Rainbow", Scientific American 236, 116, 1977

There is much more to this subject. Useful discussions and other references appear at

http://eo.ucar.edu/rainbows/
About Rainbows

http://www.ams.org/featurecolumn/archive/rainbows.html
The Mathematics of Rainbows

[jimsaruff]

This site (which I bookmark as OPOD) is, just like APOD, worth a daily visit:

http://www.atoptics.co.uk/opod.htm

[apodman]

This site (which I bookmark as OPOD) is, just like APOD, worth a daily visit:
http://www.atoptics.co.uk/opod.htm

Looks like it might have the potential to educate me, and in the long run to help me better understand an APOD or two, so I've also bookmarked it to give it a shot. Thank you for the link.

[jimsaruff]

Well, you are certainly welcome!

The gentleman who publishes OPOD doesn't mind answering questions, either.

Here's one maybe you can help me with:

What if the universe were a giant ('gi-normous' the kids might say!), nevertheless expanding, crystal?

If the 'interior' surfaces of the crystal were able to endlessly reflect 'interior' microwave radiation, would it appear to an observer inside the crystal as if, no matter where in the crystal they were, they were always at the center?

[apodman]

I started to say "no", but now I'm thinking "maybe", so I guess I don't know. Let me build a model and get back to you, but don't hold your breath waiting for an answer.

[rstevenson]

What if the universe were a giant ('gi-normous' the kids might say!), nevertheless expanding, crystal?

If the 'interior' surfaces of the crystal were able to endlessly reflect 'interior' microwave radiation, would it appear to an observer inside the crystal as if, no matter where in the crystal they were, they were always at the center?

But what would it be a crystal of?

Rob

[neufer]

What if the universe were a giant ('gi-normous' the kids might say!), nevertheless expanding, crystal?

If the 'interior' surfaces of the crystal were able to endlessly reflect 'interior' microwave radiation, would it appear to an observer inside the crystal as if, no matter where in the crystal they were, they were always at the center?

It is assumed that we are observing an hot opaque plasma that is receding so fast that it appears to be a 3K black body background.

If, instead, we are observing a reflecting crystal surface but one that is also receding that fast then we can only be observing reflected interior photons of truly enormous initial energy. Only a stationary reflecting crystal surface would return impinging 3K photons without a significant energy loss. But what is going to happen when the expanding universe hits that stationary reflecting crystal surface?