Astronomy is the science that deals with the origin, evaluation, composition, distance and motion of all bodies and scattered matter in the mysterious universe.
All along there has been a mystery regarding the beginning of creation of the universe (i.e., the world, the whole system of created things: Jahan, Alam). Science theology and philosophy have had different conceptions about it. They fail to explain the universe beyond certain limits.
Perhaps in the beginning the universe was a limitless boiling ocean of thin vapor of matter. Some people believe that originally matter was uniformly distributed in the space and from this matter were congealed out (changed from fluid to solid by cold) the heavenly bodies, perhaps in the beginning God said, ‘let there be light’ and there was light. Some people think that originally the space was flooded with light, which translated itself into energy. According to this view, Energy lay motionless over a limitless space and for ages on end there was no indication of cosmos (kai’nat- the world as an orderly or systematic whole).
Later on in the course of time, the energy took the shape of incandescent vapors of matter distributed uniformly in space. Where from this original energy came? Our science and philosophy have no reply to make. As a matter of fact our conceptions are essentially contracted by our environment of definite space and definite time and we cannot go out of these to investigate what lies beyond their confines.
Mysterious formation of the universe
Presuming, therefore, that somehow or other all the substance of the presents stars and nebulae (clusters of distance stars forming misty clouds) was at first, spread out uniformly throughout the space, it is stated by Hubble that a force of attraction (called gravitation) was thrown between the particles (molecules, as they are technically called) of this unbounded ocean of the thin matter.
Henceforth every particle of matter in space could be held in equilibrium only by an exact balancing of the forces of attraction exerted between itself and its neighbors. And it became impossible for any particle distributed from its original position to regain that state.
Therefore, the vapor separated out in myriads of condensation which dotted all around the regions of space. Each of these condensations held together its particles from flying away by attractive gravitational forces exerted by its center. As a result of the gravitational un-stability, the condensations began whirling round in such a way that their motions generated forces which sustained and overcame the gravitational un-stability and the component vapors of each individual condensation began rotating about a center. That was essential for gravitational stability.
The rotation in a mass of un solidified matter also caused another change in the shape of condensation. It got flattened in an orange like shape. As the rotation increased, the flattening also increased.
A further step in the building up of the universe now took place. As these condensations rotated they also underwent contraction, with corresponding increase in the speed. This rotation and contraction continued till at last the flattening process reached their height and gave raise t further split-up into smaller condensations; for example the star, nebulae etc, as we find them today. This is how Hubble has accounted for development of the universe.
General structure of the mysterious universe
The invention of telescope brought about a great change in the astronomical outlook of man. Something is now known about the structure of the universe. The sun is the star in Milky Way (Kehkeshan), an assembly of some 300,000 million stars, about 150,000 million years across and between 25,000 and 40.000 light years thick. The total mass of the galaxy is about 160,000 million times the mass of the sun; the mass of the sun is about 2x(10)27 tons. The whole of this system is rotating about its center of gravity. The sun takes about 225 million years to complete its orbit round the Milky Way.
In the space beyond the Milky Way other system of stars, of approximately the same size as the Milky Way, are scattered at fairly regular intervals throughout the space that our telescope can explore. The systems are called extra galactic nebulae. It is thought that about 30 million of them are visible. The average distance between two nebulae is about two million light years.
The universe is finite
Einstein’s theory of relativity maintains that the mysterious universe is of finite size. It does not mean, however, that there is an edge to it beyond which there is something which is not included in the mysterious universe. The theory tells us that space itself is curved. The universe is a three dimensional sphere (involving length, breadth and height) in which the straightest possible line returns in time to the starting point, as on the surface of the earth. The theory further considers that the universe is either contracting or expanding.
The expansion of the universe
It has been observed that the extra galactic systems are all receding from us with velocities which increase proportionally to their distances. Similarly, the distance of any nebula from any other nebula must also be increasing, at a rate proportional to their mutual distance. This is held to show that the universe is expanding. This may or may not be so. Possibly, this mysterious universe may oscillate between a certain maximum and a minimum limit with a finite period of oscillation. Astronomers are not definite about it. All that can definitely be said is that at present the universe is expanding.
The age of the universe
When did the earth, the stars and the nebulae come into existence? Basing on geology (Ilme Tabaqat-ul-Arz), the science relating to the history and development of earth’s crust, together with the several floras and faunas (which have successively clothed and peopled its surface), the age of the universe is some 3,000 million years. But there still exists controversy over the age of the sun and other stars. They may be several million years old or only a few thousand million years. Eddington used to maintain that the universe began in about 90,000 million B.C.