When I look up at the sky on a clear day, there is the sun, then a surrounding c…

When I look up at the sky on a clear day, there is the sun, then a surrounding circle of white-blue light covering maybe half the sky, encircled by deep blue down to the horizon, followed by a white layer at the horizon itself. Please explain these zones.

The ring that you see surrounding the sun is probably the 22° halo caused by refraction from ice crystals in the upper atmosphere. These tiny ice crystals are hexagonal prisms and they deflect the light that passes through them to form a ring of light around the sun. Because the particles are large enough to bend all the colors of light equally, the ring appears white—or blue-white when superimposed on the blue sky. The deep blue of the surrounding sky is caused by Rayleigh scattering of the sunlight passing through it. In this process, small groups of air molecules and tiny dust particles deflect sunlight toward your eye. Since they deflect short wavelength light (blue light) more effectively than long wavelength light (red light), they give the sky a bluish glow. Finally, the white appearance of the horizon is probably light scattered toward your eyes by surface haze. Relatively large particles in the air scatter sunlight in all directions so that you see a white glow from the air near the ground.

A wonderful reference for some of these ideas is “Rainbows, Halos, and Glories” by Robert Greenler.

Can you see out of sunglasses which shade both horizontally and vertically polar…

Can you see out of sunglasses which shade both horizontally and vertically polarized light?

No. Such sunglasses would absorb all light and would appear black. Polarizing sunglasses are designed to absorb only horizontally polarized light; the light associated with glare. There is no reason to absorb vertically polarized light.

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

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.

How does light create heat?

How does light create heat?

Actually, some light is heat. Heat is the energy that flows from one object to another because of a difference in their temperatures. The sun is hotter than you are so that it sends heat toward you. Sunlight is heat; it is the sun’s heat being sent toward you as electromagnetic radiation. When it strikes the surface of your skin, this radiation is absorbed and becomes the more familiar form of heat: kinetic and potential energy in the atoms and molecules. From the surface of your skin, this heat flows inward to warm the rest of your body. Any material that absorbs light usually converts it to heat. The charged particles in that material move under the influence of the light’s electric field and these moving charged particles transfer their energy here and there as heat.

Why are tanning beds not good for you; also there are some new ones recently tha…

Why are tanning beds not good for you; also there are some new ones recently that claim that they are safer than others (have no B rays)? Are they about the same as the sun itself or how much worse for you?

Tanning beds emit ultraviolet light in order to trigger your skin’s tanning response. This ultraviolet light can and does cause chemical damage to your skin. Like all light, ultraviolet light is absorbed and emitted as particles. The energy in each light particle depends on its wavelength and, since ultraviolet light has short wavelengths, ultraviolet light particles carry lots of energy. They carry enough energy to rearrange the molecules that absorb them. If those molecules are part of the genetic information of a cell, the cell may die or, worse yet, may become cancerous. The shorter the wavelength of the ultraviolet light, the more energetic its particles and the more damage it can do. Tanning beds walk a narrow line between inducing tanning and causing significant damage. Leather skin is one end result of too much chemical damage. Tanning beds that emit relatively long wavelength ultraviolet are probably less harmful than those that emit shorter wavelength ultraviolet (these wavelength ranges are sometimes designated by letters A, B, and C…I think that A is the longest wavelength and least harmful). Still, you skin’s tanning response is a defense against chemical damage and is probably not worth trying to trigger with light. Recent research seems to have found chemicals that trigger tanning. These chemicals mimic light-damaged molecules in your skin. Your skin senses these molecules and responds by tanning. If these chemicals work, you’ll soon be able to develop a true tan without exposure to light.