Light and Water

 

A small section of a rainbow showing the
spectrum of visible light.  Otto Lake, Alaska.

The physics is well known, even simple. Reflection, refraction, absorption.  But the interaction between water and light produces spectacular effects. 

A wine glass filled with water.  The water
appears colorless. 

Look at a glass of water. It appears clear, colorless. But if you get a long enough column of water it takes on a blue hue.  Look down into a deep lake or the ocean and the blue color jumps out at you. Water absorbs the red wavelengths of light leaving the blue light and giving it the color.  

The Atlantic Ocean off Hatteras, North Carolina.
The ocean here is deep and appears deep blue because the red wavelengths
of light are absorbed by the water.  

Crater Lake fills the caldera of an ancient volcano.
The lake is nearly 2000 feet deep and is deep blue. 
Crater Lake National Park, Oregon. 

In addition to absorption, reflection also contributes to the color of water.  Reflection from the sky can change the appearance of water.  A cloudy, gray sky will be reflected from the surface and give a completely different look to water.    

Gray sky reflected on the surface of
Kachemak Bay, Alaska.

Sunrise and sunset reflected in water can produce dramatic colors.  As the sun moves, the reflections on water change with great speed.  

A beautiful sunrise reflected in Murrells Inlet,
Georgetown County, South Carolina. 

Pink morning light on Lake Norman, Mecklenburg County, North Carolina. 

Warm sunset reflected from the surface of 
Lake Norman, Mecklenburg County, North Carolina. 

Reflections of plants growing in water and animals standing in still water gives a mirror-like effect, and makes a nearly exact copy of the original. 

Snowy Egret (Egretta thula) and its reflection.
Huntington Beach State Park, South Carolina. 

Water plants reflected in still water.
Green Cay Wetlands, Palm Beach County, Florida. 

Black-necked Stilt (Himantopus mexicana) reflected
in Radicha Creek, Kleberg County, Texas. 

Blue-winged Teal (Anas discolor) and reflection.
Wakodahatchee Wetlands, Palm Beach County, Florida. 

Some of the most amazing interactions of light and water take place in the sky.  Rainbows are made by refraction of light through tiny water drops that act as prisms. The droplets divide the white light of the sun into its constituent wavelengths of red, orange, yellow, green, blue, indigo and violet.  This is the spectrum of visible light.  Many of us learned the famous mnemonic, ROYGBIV, to keep the order of the rainbow colors straight.  In a rainbow, red is on the outside of the arc and violet on the inside.  

Rainbow at Otto Lake, Alaska. 

We view rainbows with our backs to the sun. Each color, each wavelength, is refracted a different amount causing the rainbow to form.  A rainbow is really circular, but often part of the circle is below the horizon so we see it as an arc. The angle of refraction of light in a rainbow is about 42^o so the rainbow fills an 84^o section of the sky.  

Sunbow and sundogs.
Sax-Zim Bog, St. Louis County, Minnesota. 
Photo courtesy of Ms. Judy Walker. 

Another refraction-based phenomenon is a sunbow or halo.  A sunbow is a spectrum in a circle that surrounds the sun.  Sunbows are caused by refraction of sunlight through ice crystals and the angle of refraction is 22^o.  This refraction produces a halo that fills 44^o of sky, about half that of a rainbow.  Since sunbows have a smaller angle than rainbows you are much more likely to see the entire circle of a sunbow. The order of colors in a sunbow is the opposite of a rainbow with violet on the outside and red on the inside.  

Sundog. Huntington Beach State Park, South Carolina. 

Sundogs are related to sunbows and their technical name is perihelial arcs.  They are another refraction effect caused by ice crystals and are found at 22^o to the right and left of the sun.  Sundogs sometimes appear isolated and other times are associated with sunbows.  There are sundogs in the photo of the sunbow above. 

Interactions between light and water have significant cultural meaning around the world. In ancient Greek mythology, Narcissus fell in love with his own reflection in a pool of water and stared at it until he died.  This story gives us the term narcissism.  Rainbows are considered deities in diverse cultures.  Many Australian Aboriginal groups revere the Rainbow Serpent and in ancient Greece, Iris was the rainbow goddess.  Hawaii is renowned for its rainbows and there the goddess Anuenue took the form of a rainbow and served as a messenger for her immortal brothers.  In the Genesis, God sent the rainbow as a sign to Noah that the world would not destroyed again by flood.  Ancient Norse mythology has a Rainbow Bridge from Asgard to Earth.  In our time, the rainbow flag has become the banner for gay pride. On a lighter note, Ireland gave us the story of a pot of gold at the end of the rainbow, guarded by a leprechaun. In the Wizard of Oz, Dorothy longs to go over the rainbow from a monochrome Kansas.  Science and culture give us different views of water/light interactions.  This is a measure of the impact these phenomena have on all people. 

Sunset reflected in Lake Norman,
Mecklenburg County, North Carolina.