Category: sunlight

Why does purple bend more in a prism than, say, red?

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Why does purple bend more in a prism than, say, red?

Purple (or violet) light travels slower in most materials than does red light. That occurs because violet light is higher in frequency than red light and gives the charged particles that it jiggles about less time to move up and down. With very little time to move, these charged particles barely notice that they are parts of atoms and molecules and respond easily to the passing electromagnetic wave. But when red light pushes and pulls on charged particles, there is more time for them to find the limits of their freedom. These charged particles are not able to move so easily when pushed on by a passing wave of red light so they do not interact with that passing wave as well as with one of violet light. Thus red light passes by with less effect and it behaves more like it would in empty space. Violet light, which interacts relatively strongly with the atoms it passes, slows down more than red light. Since red light travels more quickly than violet light, it bends less in passing through a prism. Violet light slows down more and bends more than red light.

What causes the colors in the aurora borealis?

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What causes the colors in the aurora borealis?

These colors come from the atomic fluorescence of particles high above the earth’s surface. As charged particles from the sun’s “solar wind” spiral through the earth’s magnetic field toward its poles, they collide with one another and with atoms in the earth’s upper atmosphere. The energy of such collisions can excite the atoms involved and cause them to emit light.

Why doesn’t light go through the other side of a water droplet, refracting as it…

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Why doesn’t light go through the other side of a water droplet, refracting as it goes through, rather than reflecting back?

Actually, 96% of the light hitting the “other side of a water droplet” does pass out of the droplet. What you see in the rainbow is the 4% that reflects back from the far side of the water droplet. If all of the light reflected, the rainbow would be much brighter.

Does a mirage operate under the same principle as the puddles on a road?

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Does a mirage operate under the same principle as the puddles on a road?

Not exactly. A puddle contains water, which reflects light directly. Light from the blue sky travels toward the puddle and illuminates it. As the light enters the water, with its higher refractive index, part of the light reflects. You see this light when you look at the surface of a puddle. But a mirage involves refraction (bending) of light. As light from the blue sky enters a regions of hot air near the surface, that light bends upward. You again see light from the sky, but bent upward by the air rather than being reflected upward by a surface of water. Since the two appear similar, you interpret the shimmering blue light of a mirage as coming from a pool of water. But it is just hot air.

Does air pollution contribute to the blueness of the sky (make it bluer)? Has th…

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Does air pollution contribute to the blueness of the sky (make it bluer)? Has the sky become more blue with the advent of technology (factories, machinery, etc.)?

Yes. Pollution does tend to make the sky bluer and the sunsets redder. However, pollution also imparts colors directly by absorbing certain wavelengths of light. The orange haze that hovers over cities is often caused by nitrogen oxides, which are simply orange in color and act like pigments to make everything appear orangish. However smoke and dust certainly change the look of the sky by increasing scattering. Natural disasters are even more effective: volcanic eruptions create the most beautiful sunsets of all by tossing vast amounts of dust into the air.

What is black light and how does it work?

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What is black light and how does it work?

Black light is ultraviolet light. You cannot see it so a room illuminated only by ultraviolet light appears dark or “black”. However any fluorescent materials in the room (e.g. brighteners in your clothes) will absorb the ultraviolet light and reemit it as visible light. That is why things with fluorescent pigments on them glow when illuminate by black light.

Why is it any worse to observe a solar eclipse rather than a normal glimpse at t…

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Why is it any worse to observe a solar eclipse rather than a normal glimpse at the sun?

The problem with looking at the sun during a solar eclipse is not that it is somehow brighter than normal but rather that (1) you tend to stare at it and (2) the size of its bright region is reduced so that it doesn’t hurt as much to stare at it. It’s hard to stare at the full sun because it feels uncomfortable but looking at a tiny part of the sun may not feel bad enough to make you avert your eyes. Nonetheless, that tiny part of the sun can cook your retina and cause permanent damage.