Equipped with this "pan-spectral" vision, we can observe things that are familiar yet unseen, as well as new things totally outside the realm of our visual sense. An example of the former is our skeletons that are revealed through x-ray imaging (we know bones are inside us, but we cannot normally see them, except teeth.) An example of the latter is the mysterious object at the center of our galaxy, hidden from our limited visual sense by intervening dust clouds, but revealed by radio telescopes as one of the brightest radio objects in our sky, Sagittarius A.
Alien Vision contains many interesting pairs of images of the same scene or object: one image made with visible light, the other with light from a non-visible region of the spectrum. For example, a yellow butterfly reveals patterns visible only in the ultraviolet, patterns intended to attract mates that can see ultraviolet light. Another example is a pair of images of a man wearing multiple layers of clothing concealing a secret: a pair of handguns. Passive millimeter-wave imaging sees the "glow" of his body heat shining through his clothes; the guns are thrown in sharp relief because they glow differently than human skin.
Showing pairs of images or series of images in different bands of the spectrum reinforces the idea that our visual spectral range is severely limited without the aid of technology. This fact is important and interesting, but difficult for many people to comprehend without visual examples. Alien Vision presents these examples with clearly written text and an extensive glossary of terms in the back of the book.
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