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.

Even
After
All this time
The Sun never says to the Earth,

"You owe me."

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

― Hafiz

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

REFERENCES

• Don't Paint the Sky Blue! by Courtney Jordan, 29 September 2013.
• Why is the Sky Blue? NASA.
• Why Skies are Blue Instead of Purple by Michael Schirber, ABC News, 19 July 2005.
• Why is the Sunset Red? by Jerry Coffey, Universe Today 31 October 2010.

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


REFERENCES

• Breaking Wave, Wikipedia.
• The Waves, by Virginia Woolf.
• Waves and Shallow Water, Wikipedia.

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

REFERENCES

• A Simple Formula to Estimate Settling Velocity of NaturalSediments, Jose´ A. Jime´nez1 and Ole S. Madsen, Journal of Waterway, Port, Coastal and Ocean Engineering © ASCE, March/April 2003.
• Erosion, Wikipedia.
• Principle of Lateral Continuity, Wikipedia.
• Sedimentary Rock, Wikipedia.
• Sedimentation, Wikipedia.
• The Feynman Lectures on Physics, Richard P. Feynman

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:

EDWARD
Dazzle mine eyes, or do I see three suns?

King Henry VI, Part 3

RICHARD
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.

EDWARD
'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.

REFERENCES

• Henry VI, Part 3, Wikipedia.
• Parhelion, Brittanica.com.
• SnowCrystals.com - A Snowflake Primer, Cal Tech.
• Sun Dog, Wikipedia.
• Sundogs: Spots of Color Beside the Sun, Live Science.