The sun is the star- nearest to earth- and one of average size and characteristics. Its supreme importance to us is due to its comparative nearness, for the light from the nearest of the fixed stars takes about 4 1/2 years to reach us, while that of our luminary (i.e., the sun) takes only some eight minutes.
The sun is the central body of the solar system, of which our earth is a member, and its immensely superior mass controls the motions of planets and small bodies which revolve round it.
The sun’s constitution
The sun is a self luminous body. The material composition of the sun has been discovered by studying its light; and it has been found that it is largely composed of metals and other heavy elements in gaseous state.
The sun is mainly a mass of intensely hot gas, the interior of which is composed to a density greater than that of water, owing to the enormous gravitational attraction between its parts. Its temperature is enormously high and varies from million of degrees centigrade in the interior to some thousands at the exterior.
Dimensions of the sun
The earth continuously travel around the sun in an elliptical orbit, and takes a year to complete the journey, our average distance from it is about 93 million miles and, as already stated, its light takes about eight minutes to reach us, travelling at 186,000 miles per second.
The sun’s bulk is enormous; its mass is 332,000 times that of the earth and its volume more than a million times, its diameter is 864,000 miles. A train moving at 60 miles per hour day and night would take over five years to traverse its circumferences.
From observation of sun spot moments it has been gathered that the sun is rotating on its axis within a period of 15 days at its equator, to nearly 27 in higher latitudes. This variation shows that the outer regions of the sun which we see are fluid. The sun does not keep a fixed position in the heavens.
Astronomical observations and investigations show that it is travelling through space at an enormous speed, carrying its family of planets with it.
Solar radiation and temperature
The sun is contentiously radiating energy into space. Only a small part of this energy is intercepted by the earth and planets, the remainder passes away into space. A large part of the portion of energy that falls on the earth is absorbed by the earth’s atmosphere.
The temperature of the sun’s surface is stated to be about 6,000o C. the temperature at the center of the sun is stated to be in the neighborhood of twenty million degrees. Our earth receives only one part in 2,200 million of the energy radiated by the sun, yet it amounts to an average of five million H. P. per square mile of surface.
The sun’s atomic energy
We depend on atomic energy for our food, for clothing and shelter and for comfort. As a matter of fact, all that we are and all that we owe, we owe to the sun’s atomic energy which the sun sends to the earth day by day.
Botanists do not know just how the leaves of plants using soil, air and water prepare and store in their leaves, stems and roots the food needed by human beings and animals, but they do know that the sun must shine on the plants for this work to go on. If there were no light of the sun as well as its heat there would be no plant life, and therefore, no food.
What is true of grains, vegetables and fruits, is equally true for meat and dairy products. There must be sunshine to provide grass, hay and grain, the food for cattle, sheep and goats. These animals are really turning the products of sun shine, or atomic energy, into meat, milk, butter and cheese.
Thus all our food is due to the sun’s atomic energy. Plants are the factories; sunlight the power; and soil, water and air are the raw materials.
Apart from feeding, sunlight clothes us; cotton grows only where there are at least eight months of warm sunny weather. The same grass that provides meat and dairy products gives us wool and leather. Mulberry leaves grown in the sunshine give us silk.
Even the material of our homes can be traced to the same source. Timber comes from trees which can not grow without the light and warmth of the sun. The paint and paper on the walls, the rugs on the floor, and nearly all parts of our furniture are traceable back to the same origin as our food and clothing. Besides all these, the light and heat in our homes which make our surrounding comfortable and cheerful come from the same heavenly body.
Electricity although directly derived from water, indirectly it is the product of sun shine, which evaporates water to form into clouds, to rain, lastly to flow in rivers which produce hydro-electric power.
We derive energy to move about, to travel, to do work, from the sun. The energy of our muscles has come to us indirectly from the sun. If we walk, our power is from the sun. If we ride an automobile, our power is from the source.
Petroleum from which gasoline is obtained comes from rock which, like coal, were formed millions of years go. The sun’s heat causes winds to blow. Air heated by the sun is lighter than the cold air and is pushed onward by the cold; and thus wind is produced. A sailing vessel is propelled by the sunlight of its own day (wind), but a vessel which uses coal or oil is using stored sunshine.
It is the atomic energy of past ages which does nearly all our works. With its power we travel by land and by sea. It carries our goods from one corner to another. Airplanes fly over the land; submarines dip beneath the seas.
Unfortunately much of the destruction of warfare is done by the airplane and the submarine. Man would be much wiser if he saved the great forces which nature has stored up in the past and put them to uses which would make all mankind prosperous and happy.
The light of the sun
Generally it is regarded that the light of the sun is yellow. It is however, much whiter than the light from ordinary artificial source of light. The light of the sun is nearly half a million times that of the full moon. Each square centimeter of the sun surface shines with a light equal to about 50.000 candle powers.
Maintenance of the sun heat
The sun radiates enormous energy in the form of heat and light. It has been radiating this enormous energy for the past thousand of million years, but it is still the seed of terrific energy and there has been no appreciable decrease in the internal store of the heat of the sun.
In case the stellar magnitude of the sun were to decrease by half a magnitude equivalent to a decrease in the sun’s brightness, to two third of its present value, a universal ice age of the earth would result.
On the other hand, the energy also does not increase, for, if it were to increase by one magnitude, the temperature of the earth would rise to the boiling point. It is probable that, in either case, life would cause to exist on the earth.
As a matter of fact, the sun has been maintaining the heat, although not absolutely regularly, because geological evidences has indicated that there have been alternations of warm period and ice-ages in the past history of the earth. The variations have, fortunately, been small in amount. By what process this is achieved, has been a matter of controversy.
Surface of the sun
Photographs of the sun taken through the telescope show many peculiarities and irregularities on its surface. Its structure is not uniform, but appears to be speckled and granulate (broken into grains or small masses) changing rapidly at different time and places.
This is probably because of moments of gaseous layers of varying luminosity. Although the sun looks like a flat disk to the naked eye, the photographs proves its globular nature by a darkening haziness around the edge, and by the force shortening of sun spot as they approach the edge of the disk. The bright surface covering the sun is called photosphere.
The most remarkable feature of the solar surface is the presence of a number of dark patches called sun spots. They are seen through a telescope with colored glass. A sun spot is funnel shaped vortex whirling motion of a fluid forming a cavity in the center: a whirl pool in the outer regions of the sun.
With this vortex, gaseous matter streams spirally upwards and outwards. As the matter streams out of the funnel shape mouth, it expands rapidly. The expansion produces considerable cooling. The emitted gases flow more or less radial outwards from the spot along the surface. They vary greatly both in size and duration.
Some of them disappear in the course of a few days, other survive for one or two revolution of the sun. They very rarely last more usually greater in longitude than in latitude. The actual drift may amount to several thousand miles in the course of a day.
It has been found that the sun spots occur in cycles. There activity is waxing or waning in a period of eleven to twelve years, when they are once again at their maximum or minimum. It has been claimed that their activity has a definite effect on earth’s magnetism.
When sun spots are numerous, magnetic storms (disturbances in the magnetism of the earth or air which cause the magnet needle to move rapidly backward and forward when telephone circuits are likely to be interfered with) are relatively frequent; when sun spots are few numbers, the storms are rare. All the same, the presence of sun spot is not the necessary and only condition of a magnetic storm. There are other factors as well.
See also: Solar aclipse (A practical observation)