WHY IS THE SKY BLUE?

The sky is actually a little bit on the violet side. It only looks blue because your eyes are much more sensitive to blue light than to violet light.

When white light from the sun travels through clear air, it hits the molecules of nitrogen and oxygen and gets scattered a little bit, so it travels in a slightly different direction. Since there are miles of air between you and the sun, the light will scatter many times.

But how much the light is scattered depends on the color. Blue light is scattered about 10 times more than red light. This is called Rayleigh scattering, after the man who worked out the math.

Violet light is the light that is scattered the most out of all the light your eyes can see. This is why the sun looks yellow to you: white light from the sun will look yellow if you remove the violet light by scattering it away.

But your eyes are not very sensitive to violet light. They are very sensitive to blue light. They are also sensitive to green light and red light. A little bit of the violet light excites the red light sensing cones in your eyes, which is why violet looks like blue with a little red in it. It is also why the sky looks light blue instead of deep blue.

When the sun is near the horizon, there is more air between it and your eyes. The light near the sun has more red and yellow because light that is scattered only one or two times does not change direction much. There is also more dust and smog, which scatter more red and yellow light. So sunsets are red, yellow, orange, and pink.

WHAT IS PLASMA? - PLASMA BASIC INFORMATION

Plasma is a gas that is so hot that the molecules or atoms lose some of their electrons. On Earth, the most common forms of matter are solid, liquid, and gas. But in the universe as a whole, the most common form of matter is plasma.

The sun is a big ball of plasma. Lightning is a plasma. The electric sparks you get from static electricity are made of plasma. There is a plasma inside every glowing fluorescent light tube and every neon light.

Plasmas consist of electrons and the positively charged atoms the electrons were stripped from. These atoms that are missing electrons are called ions, and we say that the gas that has become a plasma has been ionized.

Gases that have only a small percentage of their atoms stripped of electrons are said to be weakly ionized. When more of the atoms are affected, the plasma is said to be highly ionized.

Most flames are weakly ionized plasmas. Sparks and lightning can be highly ionized.

Because electrons carry a negative charge and stripped atoms carry a positive charge, plasmas can conduct electricity. Gases do not conduct electricity.

Plasmas can emit colors just like flames do. The color of a neon light is due to excited electrons falling back into their normal energy levels, emitting light to lose the extra energy.

Other plasmas emit other colors, since their atoms or molecules have different energy levels. Helium plasmas are pink. Plasmas made from sodium vapor are the characteristic yellow of sodium.