Lecture: Color and Light in Nature
Joanna Gaunder
I am a devotee of beauty, so when I heard about
a lecture entitled "Color and Light in Nature," I was
there, even though it meant giving up a portion of my Friday night.
The lecturer was Dr. David Lynch, a senior scientist at Aerospace
Corporation -- not to be confused with the eponymous director of
Twin Peaks and Mulholland Drive. The lecture covered all major phenomena
of light and color up in the air, including rainbows, haloes and
the green flash.
On April 30, arriving early to Room 140 of the science building,
I spoke with Dr. Lynch about his interests. He plays fiddle for
a band called the Squirrelheads, he went to Indiana University and
the University of Texas, and he has lived in California for 30 years.
His professional interests pertain to stars, especially star birthing
grounds in faraway galaxies.
Twice a year, Dr. Lynch and his team of astronomers go to Mauna
Kea, atop a 14,000-foot mountain in Hawaii, but they don't actually
look through the telescope. No one does anymore, because the telescope
is too much in demand. Research teams have their equipment hooked
up 24/7. So it is at observatories everywhere.
Dr. Lynch does not own a telescope at his home in Topanga. The stars
are so far away, he told me, that they don't "resolve."
No matter how strong a telescope you use, all you can see when you
look at a star is a pinpoint of light -- not a disc with a top and
bottom as when you look at the sun.
Dr. Lynch's presentation covered 55 different optical effects, all
visible to the naked eye, and tips and tricks for spotting them.
The pace was fast. I tried to take thorough notes and still sink
into the awesomeness of the slides; it was a balance.
The major topics were rainbows, shadows, water, snow, haloes, sunsets
and the green flash. I'll give a brief rundown of each.
Rainbows
There is always a fainter secondary rainbow next to the one you
see, because that's how the optics of water droplets work. If the
water droplets are the size of peas, there will be supernumerary
rainbows (more than just two), but there are always at least two.
All rainbows are in fact full circles, but you have to be looking
down from above to see all three hundred sixty degrees.
Rainbows are polarized, which means they disappear if you try to
look at them sideways through a polarized lens.
Fog washes out the color of a rainbow and you see white rainbows
or "fogbows."
Sometimes you can see very faint "cloudbows" out of airplane
windows.
When looking for a rainbow, always put the sun at your back.
Shadows
Next time you see a sunset, notice the line where a band of pink
meets a band of blue: the blue is the earth's shadow. Every evening
at twilight, the shadow of the earth is cast upon the sky.
Sunbeams filtering out from a cloud, also called Ropes of Maui and
Rays of Buddha, are actually parallel shadows that appear to converge
(a perspective effect, as with railroad tracks). If you look carefully,
you will notice that each "sunbeam" is actually the shadow
of a bit of cloud.
Water
“Water,” says Dr. Lynch, “is most interesting
when it has waves on it.” Steeper water appears darker. An
example from sailing is the “cat’s paw,” a dark
patch on the water created when the wind musses the surface tension.
Have you ever seen a glittery patch of moon reflected on water?
It consists of tiny rings of light, instantaneously forming and
disappearing. “Just keep looking -- they come and go fast.
You must expect to see them,” said Dr. Lynch. “And you
must have a camera with you.”
Snow
Water is blue. Ice is blue. Why is snow white? Because anything,
even black coal, looks white if ground up finely enough. Crystals
have tiny surfaces and “white” just happens to be the
way light reflects off of them. It’s a rule of optics.
However, if you put on enough pairs of dark sunglasses, you can
see colors in snow. To demonstrate, Dr. Lynch put up a photo of
snow taken with underexposed film. It appeared glittery black with
gold flecks.
In a whiteout, due to the way the light reflects off many small
crystals, there are no shadows. There is uniform illumination all
around. Hence there is no color contrast (because it's all snow)
and no brightness contrast (because of the absence of shadows),
which means your visual system cannot perceive what you are stepping
on, and you could step right off a cliff. Conclusion: don’t
walk around in a whiteout!
Haloes
Put your fist over the sun and take a picture. There’s a good
chance you’ll see a white ring around the sun when you get
the film back: a 22-degree halo or "common halo." The
common halo forms in high, thin, wispy cirrus clouds, which are
made of tiny ice crystals. There is also a 46-degree (broader) halo
sometimes visible.
The aureole around the sun is white, and the sky is also white,
around the horizon. The sky’s blueness varies with distance;
it is darkest blue straight overhead. There is a whole science devoted
to the way light scatters in the sky.
Sunsets
When Mount Pinatubo erupted in the Philippines, it changed the world's
sunsets for a few years until the dust settled. In Southern California,
we get a similar effect whenever there is a brush fire. In a smoggy
sunset, the earth's atmosphere becomes like an astigmatic lens and
the sun appears oval, squashed.
The Green Flash
If you live by the beach, you have probably heard of the “green
flash” when the sun sets over the water. You don’t have
to live near water to see it, but you do have to be someplace very
flat, so the ocean is a good bet. The green flash comes from very
top of the sun’s disc, the very last little part to go down.
It lasts for about one second, and you have to be sneaky to see
it: you have to know ahead of time exactly when to look. If you
dazzle your retinas by looking at the sun too soon, you will miss
the green flash.
In exceptionally clean air, it is possible to see a blue or even
violet flash following the green, but those are rare.
Among the photographs, there were a few shots that used specialized
photographic effects, including a great timed exposure of the full
moon rising (it actually stays the same size throughout its rise),
but most of the slides came from simple point-and-click camera shots
-- amazing pictures of ordinary skies. Dr. Lynch emphasized over
and over, “These things are easy to see. You just have to
look up.”
David Lynch coauthored a book with Bill Livingston called "Color
and Light in Nature." It is for sale at Amazon.com. http://www.amazon.com
An excellent page on the Green Flash by Andrew T. Young:
http://mintaka.sdsu.edu/GF/index.html
Joanna Gaunder is an Internet and Media Consultant
who works both privately and for an international corporation and
resides in the Venice area.
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