All life on the earth depends on the sun for heat and light. The development of life on the earth was made possible by the steady flow of light and heat from the sun. Life would be endangered if the sun’s heat and light were to vary: it would be too hot or too cold to live. Life also depends on the sun for food. The heat of the sun is trapped by the atmosphere which lets sunlight through to the surface of the earth. The light warms the earth but the heat it creates cannot easily pass through the atmosphere into space.
This is known as the “greenhouse” effect. It is what happens when the glass roof lets the sunlight in to heat the plants in the greenhouse but it passes back through the roof only very slowly. All living things, both plants which make their own food through photosynthesis (they combine energy from sunlight with carbon dioxide from the air and water from the soil to make food). In the process they give off oxygen. Men and animals breathe this oxygen released by the plants and exhale the carbon dioxide which in turn is used by plants.
Sunbath is the exposure of the body to sunlight or to sun lamps. Sunlight is made up of many different kinds of light rays. Infrared ray penetrate deeply into the body. They benefit the circulatory system and the muscles. Ultraviolet rays are chiefly absorbed by the skin and may cause sun burns and tanning. They also caused chemicals in the skin to produce Vitamin D, the sunshine vitamin. Sun lamps produce ultraviolet rays. The importance of the Sun was realised by the ancient peoples of India, Egypt and Greece.
They worshipped it, made offerings to it and built temples to honour it. Today we acknowledge the sun as a source of light, heat and other kinds of energy. Life of men, animals and plants depends entirely on the energy of the sun. As we explained earlier, plants use sunlight to make their own food and in the process oxygen is released. Our infinitesimal position in the universe can be gauged from the fact that the life giving sun is only one of the billions of stars in the universe.