We are colorblind. Sure, many of us can see red and green, blue, yellow, orange and purple. Black, gray and white and brown (which are mixes of those other colors). But the extent of our vision ends there. A whole rainbow of colors, incomprehensibly vast, exists beyond the limits of our vision. When we feel the sun's warmth on our skin, we're absorbing infrared light. And the purpler-than-purple, so-purple-we-can't-see-it light that gives us sunburns is ultraviolet light. Although we see infrared light and ultraviolet light with the skin on our arms and our faces, not with our eyes, it is still fundamentally the same as optical light. Optical light is the name astronomers use for the light we see with our eyes - red through green through purple, the clay and the grass and the mountains.
So what determines what light we can see and what light we can feel and what light just rushes right past us? It's a property called the wavelength. If you've ever been to the ocean, then you've seen a wavelength. When I go in the ocean with my dad to go boogie boarding, I watch the wave that's closest, about to hit me. But I've also got my eye on the next wave after that, in case that's a big wave, a better ride. The distance between the two waves (maybe 30 feet) is the wavelength. Like the ocean, light washes over us in tiny little waves.
Our bodies react in different ways to different wavelengths. Our eyes are sensitive to wavelengths from 400 to 700 nanometers. Take a human hair and split it into one thousand thin strands, and each of those is the size of a wavelength of light that we can see. Infrared light is about twice the wavelength of the light we can see, and UV light is about half. Stretch the light waves out by two, putting the crests of the waves twice as far apart, and suddenly, instead of seeing it with our eyeballs we feel it on our skin. Scrunch the light together by a factor of two, so the crests are twice as close together, then instead of seeing it with our eyeballs we don't notice it at all until suddenly we have a sunburn (or worse, skin cancer).
There is light even beyond infrared and ultraviolet. That is just a small, small part of the many kinds of light out there. Radio waves, which we use to listen to NPR or POP-FM, these radio waves are light too. They're very very very stretched out light. The waves picked up by our radios are 10 feet long. So we're going from one one-thousandth of the width of a human hair to two humans tall. But they are both light.
If we go in the other direction, to very very short, we can get to gamma rays. Gamma rays have the shortest wavelength and the most energy, and they come from the strongest most powerful creatures in the Universe - violent explosions and exotic beasts like black holes. Gamma rays have a wavelength that is even smaller than the size of an individual atom. Because gamma rays are so so small, they just sneak right on through everything. This makes them very hard to detect. We definitely can't see, or feel, them with our bodies.
Astronomy is the cure for colorblindness. Using telescopes - optical telescopes and infrared telescopes (like night-vision goggles!) and ultraviolet telescopes and X-ray detectors and gamma-ray detectors and radio telescopes, we can "see" all the different wavelengths. We can look at the sky through new eyes, eyes that can see what people 100 years ago never dreamed we would see.
Take a look at the pictures here. These pictures are pictures of the Milky Way galaxy, where we live. The visible-light image (center row on the right) shows the familiar band of stars stretching across the sky that you can see when you go camping up in the mountains or out in the desert, in a very dark place. These other pictures show our same galaxy, from the same point of view, just with different "eyes" (telescopes) that see in different wavelengths. Relying on the ingenuity of engineers and scientists and inventors who built us those eyes, we can see the unseen universe.
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