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Wednesday, 21 January 2015

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Yet another imponderable observation: How did the Green Bay Packers blow a comfortable lead in the final quarter of the divisional championship (football) game last weekend?

Galen Rowell's excellent older book Mountain Light covers a lot of this material too.

Up to now, my favorite book on this subject has been the still excellent work by Marcel Minnaert, "The Nature of Light and Color in the Open Air", Dover, 1954, ISBN 0-486-20196-1. There is a nice review of Minnaert in Wikipedia, where a new translation with color photographs is referenced.

I would enjoy Ctein's take on twinkling stars and adaptive optics.

By "dark side of the moon" you mean the part of the crescent moon that isn't illuminated by the sun? I've always heard that it was illuminated by "Earthshine," or sunlight reflected from the Earth. The one question I haven't seen answered in high school science is the "green flash." Sounds like a comic book super hero.

The other one that should be on the shelf is Robert Greenler's Rainbows, Halos, and Glories which is unfortunately out of print but available in paperback used for reasonable prices. It delves into the details behind various atmospheric optics but his particular interest is halos.

He was Professor of Physics at the University of Wisconsin-Milwaukee. He also worked in the same field as me (surface science) but atmospheric optics was a "serious" sideline. I met him when I was a graduate student in the 80s and he visited our group at the University of Liverpool.

One thing he taught me is every time you walk out of a building look up. You never know what you'll find. It's the one way to improve the number of times you'll see interesting examples of Atmospheric Optics (and rare birds too).

The other thing he mentioned (now easy to do) is always carry a camera as you may find a unique example of atmospheric optics that needs to be photographed.

And speaking of atmospheric optics (and photography) here's an superb example of a supralateral arc, Parry arcs, an upper tangential arc, parhelic arcs, a 22 degree halo, a Sun pillar, a Sun dog and infralateral arc. All in one photo taken by Joshua Thomas at Red River, NM the morning of January 9, 2015. They're all in Greenler's book.

More on this (and a bigger image) at:

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2015/01/12/nine-optical-phenomena-captured-in-one-amazing-photo/

Watch the skies!

"the green flash" is sometimes known as the "green ray" and it provided the closing scene in Eric Rohmer's film "le Rayon Vert"
http://www.imdb.com/title/tt0091830/

Will reading this affect my "scenic" photography? ;>D

#8. Because of the thicker atmosphere at lower altitudes. At sunset, sunlight passes through the atmosphere longitudinally over an "infinite" distance, rather than perpendicularly (when the sun is high above the horizon) which is only 16 km thick. In Manila, pollution contributes to the fiery sunset seen in these parts. I don't know about the "flattened" part.


#15. "Earthshine." Sunlight reflected by the earth towards the moon and reflected back to us.

It's all physics....if some are not then they are metaphysics!

Great article that answers the question:

"Why icebergs are blue?"


http://www.luminous-landscape.com/essays/blue-icebergs.shtml

So, it is not a link, it is an ad!

[If it is, it's a free one. I don't know anyone connected to the book and I don't get anything if you buy it. --Mike,]

'As there is a constant flow of light we are born into the Pure Land' (Colin McCahon, NZ artist)

Such interesting and beautiful phenomena. Many of them are also shown and explained here.

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

You might also like this classic by Marcel Minnaert.
The English edition is quite a bargain, the Dutch original, in 3 volumes, will set you back €210,- ($240,-).
Nicolaas, Amsterdam.

Why is there always a lighter band around a dark object on the horizon?

My go-to book for the last few years has been John Naylor's Out of the Blue. I purchased it after a recommendation either here or on the Luminous Landscape.

Dear Phil,

Green flashes are pretty simple. The part that isn't an optical illusion (a part of it is) is simple prismatic refraction in the atmosphere. The image of the sun gets spread out slightly as a spectrum, with the shorter wavelengths towards the top and the longer ones towards the bottom. The trailing edge of the sun, the very last to go below the horizon, has those shorter wavelengths.

Photographs of green flash conditions that include the disk of the sun (I've made some) can show this clearly; for example, sunspots are chromatically smeared on the face of the sun to the same degree that the edge of the sun is.

Part of it is optical illusion––the persistence of vision thing. You're looking at a bright red-orange object. The moment it disappears there will be a persistent “negative” image which, in this case will be blue-green. It accentuates the appearance of the physically-real flash.

To see a green flash you need a view to the horizon (or an extremely low-lying, sharp-edged deck of clouds), reasonably clean air (you'll never see a green flash with a blood-red setting sun) and enough turbulence in the atmosphere to make it twinkle a bit.

They are not hard conditions to come by in the right location, but the right location may be hard to come by.

Where I live, overlooking the Pacific Ocean, conditions are excellent for seeing green flashes... except... for the marine fog layer which usually hangs 20 km or so offshore. It's not often we get clear air all the way to the horizon, and often when we do the air is stagnant enough that there is a lot of dust and other particulate matter in it and not a lot of twinkling. So, only a few times a year.

But, there was one week about a decade back when the marine layer was being pushed far offshore and the air was unsettled enough that we saw SEVEN green flashes in a period of six days. Two on one day, when there was a very thin bank of clouds that were separated from the horizon and sharply enough defined that we got a flash as the sun passed the bank of clouds and then as it passed the horizon.


pax \ Ctein
[ Please excuse any word-salad. MacSpeech in training! ]
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