Why Does The Sky Appear Blue?

            A blanket of air called atmosphere, surrounds our earth. It is mainly composed of nitrogen, oxygen, carbon dioxide, dust particles, water vapors and other gases. The light coming to us from the sun has to travel through this atmosphere.

The Sky

            We all know that the sun is the main source of light for earth. When the sunlight passes through the atmosphere, it is scattered by the dust particles, water vapor and air molecules in all the directions. This is the reason why light is all around after the sunrise.

            Do you know that the sunlight is composed of seven colors- violet, indigo, blue, green, yellow, orange and red? When the sunrays pass through the atmospheric molecules, the violet, indigo and blue colors get scattered most and the red color least of them. Therefore, when we look at the sky, the light that enters our eyes mainly consists of violet, indigo and blue colors. The mixture of these three colors is almost blue. That is why the sky appears blue.

            If the earth had no atmosphere, the sky would have just appeared dark. This fact is clear when we look at the sky from the surface of the moon. It appears dark since there is no atmosphere in the moon. Similarly, the sky appears dark when we look form a spacecraft, because there are no light scattering particles in the higher space.

What is Helium?

            Most of the gases found in nature can be prepared in the laboratory. But there are a few gases that are found only in nature. Helium is one such gas. It is an inert gas, which is odorless and tasteless. Due to its unusual characteristics, helium is a very useful gas. It is the second lightest gas, next to hydrogen but unlike hydrogen, it is non inflammable.

The characteristics of Helium

            An English scientist sir Joseph Norman Lockyer and a French chemist, Pierre Janssen, independently discovered helium gas in 1868.

            While studying the solar spectrum to find the elements present in the sun, they came across some lines that were not observed earlier. These lines suggested the presence of a new element in the sun. This element was named helium, after the Greek word ‘Helios’ meaning the sun. A number of scientists tried to detect the presence of helium in the earth’s atmosphere. They detected very small quantities of helium in the atmosphere. Did you know that atmospheric air contains only one part of helium in 1,86,000 parts, i.e., 0.0005239%?

            Due to its lightness and non inflammability, helium is used in weather balloons. Helium is also used to ease the breathing difficulties of asthmatic patients. Deep sea divers are given a mixture of oxygen and helium for breathing so that after coming back, they do not suffer form the bends. Helium is also used to weld aluminum. A mixture of helium and neon is used to produce laser beams. Helium can be liquefied at -268.90 degree centigrade or 4.2 K. liquid helium is used in low temperature work.

How is Oxygen Useful to Us?

            Oxygen is the most important gas in the atmosphere. Without oxygen, there would be no life on the earth. No living being, plants or animals, can survive without it. Do you know what it is, and why is it absolutely essential for us?

            Oxygen is a gaseous element. Two scientists discovered oxygen independently. Carl Scheele, a Swedish Chemist, discovered oxygen in 1772 and Joseph Priestley from England in 1774. It is a colorless, tasteless and odorless gas. The atmosphere around us contains 21% oxygen, 78% nitrogen and other gases about 1%.

            On the earth’s crust, oxygen is found in the forms of oxides of metals. Oxygen can be liquefied at -182.9 degree centigrade under a certain pressure. In the liquid state, it becomes light blue in color. At -218.4 degree centigrade, it is converted into solid state.

            In the laboratory, oxygen is obtained by heating a mixture of potassium chlorate and manganese dioxide. Fro the atmosphere, it is obtained by the fractional distillation of air. The air is compressed to tow hundred times the normal atmospheric pressure and passed through a narrow hole into a chamber. When the pressure is suddenly dropped, the air gets liquefied and is collected in the chamber.

            Nitrogen gas is separated form this by special method ad oxygen is obtained in the liquid state.

            All living beings need oxygen for breathing. Plants also breathe oxygen. They absorb oxygen during the light. During the day, they give off oxygen by the process of photosynthesis.

            Burning oxygen gas along with acetylene gas produces a flame of high temperature called oxyacetylene flame. This flame is used for welding and cutting metals. Liquid oxygen is also used as a fuel in space vehicles.

            Oxygen cylinders are used by patients in hospitals having breathing problems and also by mountaineers and divers in the sea. Oxygen helps in the oxidation of food in our body, which ultimately give us energy. Fuels can burn due to oxygen in the atmosphere.

            We cannot breathe in pure oxygen, as it is harmful for our body cells. Fresh air in essential for us because it contains oxygen and other gases it he correct proportion. It is for this reason that we should keep the doors and windows of our rooms open to let in fresh air.

Sea-divers take oxygen cylinders with them to breathe while in the sea

            This is the reason why one should not cover one’s face while sleeping, as it would prevent him from breathing in fresh air. During winters, one should not close the doors and window and light a fire of coal inside the room to keep warm, because during this process, oxygen is used up and carbon dioxide is released, which is very harmful.