Sensory Misinterpretation

Yes, Virginia, You Have Five Senses

Contrary to what we are taught in school, the normal complement of senses is seven. Besides the traditional sight, sound, smell, taste, and touch, we can sense heat (or the lack thereof, which we call cold) and acceleration.1 The former sense keeps us from getting burned or frozen, while the latter helps us maintain balance, feel the changing speed of a car, and thrill to a roller coaster ride.

We rely on sensory data from all seven sources continually throughout the day. As used here, "sensory data" means any information we glean directly from the natural world. It differs from most of

1 It's interesting to note that in biblical times the human soul was believed to be made of seven properties that were the influence of the five planets then known, plus the Sun and Moon. Those senses were speech, hearing, smell, sight, taste, animation, and feeling. The latter two were dropped as the definition of a sense was refined.

the other external sources of incorrect beliefs because it comes to us unprocessed by other minds. Therefore, any errors that result from evaluating this information are entirely of our own making. Experiential misconceptions are those based on misinterpreting our own sensory experiences.

When Is the Sun Not Yellow?

Consider, for example, our perception of the Sun's color. Common beliefs are that it is yellow, white, or orange. This makes perfect sense: a quick glimpse of the Sun high in the sky (and you should never look at the Sun for more than a split second without suitable protection) gives our brains the impression that it is yellow or white. Seeing it near sunrise or sunset gives the impression that it is a distinctly orange body. So which color is the Sun? All and none of these.

The Sun emits all the colors of light, as well as the rest of the electromagnetic spectrum: radio waves, infrared radiation (which we detect as heat), ultraviolet radiation, x-rays, and gamma rays. Electromagnetic radiation travels as vibrating particles called photons. Figure 3.1 shows a model of a photon and its important properties. All photons travel at the same speed (the speed of light) and the various types of electromagnetic radiation differ only in the wavelength of vibration in the photon, as shown in the figure. Indeed, all the colors of the rainbow merely represent different wavelength visible-light photons.

However, the Sun does not emit all types of electromagnetic radiation equally. Indeed, it doesn't even emit all visible light colors equally. Figure 3.2 shows how the intensity of the Sun's electromagnetic radiation varies with wavelength. Note that the most intense colors emitted by the Sun are in the blue-green part of the spectrum. In other words, the Sun emits more photons with wavelengths that we interpret as blue-green than with any other wavelengths. You might say we orbit a turquoise star.

So why does the Sun appear yellow, white, or orange? The answer has two parts. First, most of the Sun's violet and blue light, and much of its green light, is scattered in other directions by the Earth's atmos-

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