Saturday, December 28, 2013

Perceiving Sky

Ram's Head
Georgia O'Keeffe, 1935
Painting landscapes involves learning how to paint the sky. Whether our intent leans toward realistic or representational, we learn the details of perception like the sky tends to lighten toward the horizon.

We are encouraged to consider atypical skies ― the non-blue moods of the sky we frequently see.

Painting sky, we sensitize ourselves to shadows and highlights. We are reminded that clouds reflect the light in the sky.

Look at your feet. You are standing in the sky. When we think of the sky, we tend to look up, but the sky actually begins at the earth.
Diane Ackerman
Cloud Study
John Constable, 1822
White light has the visible colors of the spectrum. White light emanating from the Sun is scattered by the gases and particles in the Earth's atmosphere.

Atmospheric gases act as a prism to separate white light into its component colors. The atmospheric prism is mostly nitrogen (78%) and oxygen (21%) with trace gases like argon and water vapor. Particulates can be dust, soot, ash, pollen or salt from the ocean.

Blue light travels as shorter, smaller waves. A cloudless sky appears blue because blue light is scattered more than other colors.
All this time
The Sun never says to the Earth,

"You owe me."

What happens
With a love like that,
It lights the whole sky.

Viewing the sky away from the sun we see light that is bent the most ― a complex spectrum dominated by light of between violet (wavelength of 400 nanometers) and blue (wavelength of 450 nanometers).

Sunset at Montmajour
Vincent van Gogh, 1888
Sunset light travels farther through the atmosphere before it reaches us. More of that light is scattered.

The color of the sun itself changes from orange to red. The cooler, shorter wavelength blue light is completely scattered leaving the warmer, longer wavelengths like oranges and reds on the horizon.

The sky grew darker, painted blue on blue, one stroke at a time, into deeper and deeper shades of night.
Haruki Murakami, Dance Dance Dance


Saturday, December 21, 2013

Shoreline Waves

As swells travel toward the shoreline, the ocean floor gradually rises or there might be a disruptive change in ocean floor topography like a reef or rock ledge. As the depth of the water gets shallower, waves become higher and steeper.

Approaching the shore, the orbital motion of water is disrupted to the point where water particles no longer return to their original position. The orbital motion is shown by the red dots and blue traces above.

The Banzai Pipeline, Hāna, Hawaii

Ultimately a wave breaks when its crest overturns itself.

The waves broke and spread their waters swiftly over the shore. One after another they massed themselves and fell; the spray tossed itself back with the energy of their fall. The waves were steeped deep-blue save for a pattern of diamond-pointed light on their backs which rippled as the backs of great horses ripple with muscles as they move. The waves fell; withdrew and fell again, like the thud of a great beast stamping.
Virginia Woolf, The Waves


Saturday, December 14, 2013

Settling and Coelescence

Sandstone layering
Particles suspended in water tend to settle from the pull of gravity before coming to rest against some barrier. The settling and coalescence of Earth's fine-grained material is called sedimentation.

Sedimentation and erosion are poetically reciprocal phenomena.

If erosion is the breaking loose, suspension, and movement of particles via water, then sedimentation is the terminal end of that movement where suspended and transported particles settle out to come to rest.
"The question is, of course, is it going to be possible to amalgamate everything, and merely discover that this world represents different aspects of one thing?"
Richard Feynman, The Feynman Lectures on Physics

Sedimentary Rocks

Sedimentary rocks form by the settling of Earth's fine-grained material. Earth's fine-grained material occurs from weathering and erosion. Sedimentary rocks cover much of Earth's continents, yet the volumetric contribution of sedimentary rocks to the total volume of Earth's crust is only about 8 percent.

Lateral Continuity

The result of the settling of particles or deposition of particles is the formation of new depositional landforms. These landforms are often observed in a lateral or horizontal plane. The lateral plane is orthogonal to the direction of gravitational pull.

Sedimentary rocks separated by a valley

Layers of sediment extending laterally in all directions are said to have lateral continuity (cf. The Principle of Lateral Continuity). Sometimes the lateral plane appears to be tilted or has been interrupted by other forces.

"Curiosity demands that we ask questions, that we try to put things together and try to understand this multitude of aspects as perhaps resulting from the action of a relatively small number of elemental things and forces acting in an infinite variety of combinations."
Richard Feynman, The Feynman Lectures on Physics


Saturday, December 7, 2013

Sun Dog Prisms

Sun Dogs in Fargo, North Dakota.
February 18th, 2009.
The luminous patches that occasionally appear on each side of the sun during freezing atmospheric temperatures are called sun dogs.

According to folklore, sun dogs follow the sun like a dog follows its master.

Parhelia is the scientific term for sun dogs. Parhelion derives from the Greek parēlion which means beside the sun.

Sun dogs are an atmospheric optical phenomena. The luminous patch occurs when sunlight passes through and is refracted by hexagonal ice crystals.

The hexagonal ice crystals, falling with their long axis perpendicular to the earth, act as rotating prisms bending the sunlight. Because of the prism-like configuration of the falling crystals, sun dogs happen 22° to the left and 22° to the right of the sun viewed above the horizon.
Top View of Falling Crystal: Sunlight passing through two
surfaces of a rotating hexagonal ice crystal which is a 60° prism.

Sun dogs appear in art and literature. Shakespeare wrote about them in  King Henry VI:
Dazzle mine eyes, or do I see three suns?

King Henry VI, Part 3
Three glorious suns, each one a perfect sun;
Not separated with the racking clouds,
But sever'd in a pale clear-shining sky.
See, see! they join, embrace, and seem to kiss,
As if they vow'd some league inviolable:
Now are they but one lamp, one light, one sun.
In this the heaven figures some event.

'Tis wondrous strange, the like yet never heard of.
I think it cites us, brother, to the field,
That we, the sons of brave Plantagenet,
Each one already blazing by our meeds,
Should notwithstanding join our lights together
And over-shine the earth as this the world.
Whate'er it bodes, henceforward will I bear
Upon my target three fair-shining suns.

— King Henry VI, Part 3, Act II, Scene 1

Sunrise or sunset is the best time to observe sun dogs.