Essay 4: 11/04/2003   Astronomy, Physics, Spectroscopy

Sunlight Through Clouds of Smoke

I was walking to work earlier today and experienced an interesting phenomenon. I was outside and I
was coming out from a shadow cast by a nearby building. I felt the sensation of heat on my face and I
did not know what it was from. I looked around and realized that the only possible source of this heat
was the sun.

Usually I would not have to look around to realize that the sun is the primary source of noontime heat but
in this particular case the sun was very dim. I soon noticed that the sun was also intensely red. I knew
immediately that something was up. The sun is never that dim and that intensely warm, and it is never
red so far from the horizon. Well, something was up.

Smoke from nearby fires changed the way that I perceived the light coming to me from the sun. It made
sense that the sun was red, because smoke filters out light rays from the sun that have higher
frequencies. The following colors are in order of decreasing frequency (and increasing wavelength):
violet, indigo, blue, green, yellow, orange, and red. Because the smoke absorbed some of the sun rays
higher frequencies, the light that I saw was tinted red.

The sun emits electromagnetic radiation in a wide range of frequencies. The following types of
electromagnetic radiation are in order of decreasing frequency: gamma rays, x-rays, ultraviolet light,
visible light, infrared light, microwaves, and radio waves. The “color” that is invisible to us, but is right
below the color red in this spectrum, is infrared light. Infrared light is perceived by us as heat and
because the smoke allowed the lower frequency light to pass through, there was a disproportionate
amount of heat coming from the sun.

The sun seemed extraordinarily dim, reddish and hot to me because of this characteristic property of
smoke. A normal cloud that is made up of water vapor will block out the components of electromagnetic
radiation (light), much more uniformly.

Brownian movement: noun
The random movement of microscopic particles suspended in a liquid or gas,
caused by collisions with molecules of the surrounding medium. Responsible for the collisions that
the dispersal of smoke.

Electromagnetic Radiation: noun
Another term for light. Light waves are fluctuations of electric and magnetic
fields in space.

Gamma Rays: noun
Highly penetrating light waves that are emitted by radioactive substances.

Infrared Light: noun
Light waves that correspond to radiated heat.

Microwaves: noun
Light waves that can be used to excite, and heat up water molecules.

Radio Waves: noun
Light waves often used for the wireless transmission of information.

Raleigh Scattering: noun
The scattering of electromagnetic radiation by particles with dimensions much
smaller than the wavelength of the radiation, resulting in angular separation of colors and also
responsible for the reddish color of sunset
and the blue of the sky.

Ultraviolet Light: noun
Light waves visible to some types of animals, responsible for sun burning.

Visible Light: noun
Those light waves that can be perceived by the human eye.

X-Rays: noun
Light waves used for their penetrating power in radiography, radiology, radiotherapy, and
scientific research.
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