“Sol” is the Latin word for sun. Conception of the solar system is easy to understand. The phrase solar system means the sun and the group of heavenly bodies held in captivity by the sun. These heavenly bodies include the nine known planets (of which the earth is one), there satellites (28 in numbers), a great number of asteroids, and some other bodies like comets, meteors and meteorites whose whereabouts are still a mystery. All these bodies move round the sun in elliptical path, being held in their orbit by the gravitational force of the sun and of one another.
For a clear conception of the scale of the solar system take the sun as reduced to the size of a beach ball of 24 inches in diameter. On the same scale, roughly the nine planets would be represented thus:
Mercury = a grain of mustard seed 164 feet away
Venus = a pea 284 feet away
Moon = a grain of mustard seed 13 feet out from the earth
Mars = a currant 654 feet away
Jupiter = an orange half mile away
Saturn = a tangerine 4/5 miles away
Uranus = a plum just over a mile away
Neptune = a plum 2 ½ miles away
Pluto = a pinhead usually about three miles away
The utter remoteness of the solar system from all other heavenly bodies is stressed by the fact that, still using the same scale of two feet sun, which for this purpose we shall place in the center of, say London the nearest stars, the triple Centauri system, would lie about 8000 miles away, say in the region of London with the largest member having a two feet diameter. Only the next three nearest two stars in our Milky Way galaxy could, even on this scale, be accommodated on supply on the earth’s surface.
Man had been considering the moon and the planets among the “Fixed Stars”. The Babylonians and Egyptians could predict the lunar and solar eclipses with certainty. The heavenly bodies were considered to be gods. The common believe was questioned Anaxagoras. He considered the sun to be a red hot stone and that the moon was made or earth. He was persecuted and made to flee from Athens.
All the time people had been considering that the stars, the sun, the moon all moved round the earth. But, towards the end of the 15th century B.C. it was discovered the earth was a globe, a round body like a ball, a sphere. Some hundred years ago, therefore they measured the diameter of the earth. Then the astronomers began to measure the distance of the earth from the stars and the planets, and the magnitude of the sun and the solar system. People had many superstitions about the earth and heavenly bodies. The worshiped them. The names of days such as Sun day (Sunday), Moon Day (Monday), etc, suggest that heavenly e.g., the sun the moon etc were worshiped and in those days. People like Galileo had to suffer at the hand of ignorant and superstitious minded people for long until the invention of telescope established the falsehood of most of the superstitions forming part of religion. Newton established beyond all doubt that all the planets move round the sun. He introduced the public to the clear conception of the solar system and the laws of gravitation. As regards the origin of the solar system, Newton held that the hand of god hurled away the planets which began to move in their orbit under the influence of the law of gravitation.
The origin of the solar system
There are different stories regarding the origin of the solar system.
Theory of Laplace
Laplace conception was different. He supposes of the solar system to have originated out of a flattened mass of gas or nebula extending beyond the present orbit of Neptune, which was, at the outset, at a high temperature and in rotation. The mass gradually cooled down by radiation at its surface and at the same time contracted under the influence of its own gravitation.
Consequently, the central portion was heated and the angular velocity of rotation was increased. As the angular velocity increased, the centrifugal (i.e., tending away from the center (baeed az markaz) force at the equator), at last become greater than gravity.
Laplace supposed that a ring of matter was left behind along the equator and that further contraction detached a series of such rings. Each ring was supposed to break up and condense in to a gaseous planet which again underwent a similar process of evaluation on a smaller scale. It resulted in the formation of satellites.
This theory presupposes that all the planets were formally gaseous. The objections to the theory of Laplace are numerous and strong. e.g., the matter left behind during the contraction would not form a ring, even if the rings were produced, they could not condense into planets, etc.
The Planetesimal theory
The Planetesimal theory developed by Chamberlain and Moulton supposes an initial non-rotating gaseous mass which, under the influence of its gravitation, would be spherical in shape. If another body passes sufficiently near this mass, tidal forces are produced. As they approach to near this mass, tidal forces are produced. As they approach more closely, there tides will raise in height until, according to the theory two jets of matter will rush out from the center to directly opposite points, where the tights are highest. And as the tide raising body passes on, it will set the primary body in rotation.
The two jets of nebulous (misty, hazy, having the appearance of little clouds) matter are, therefore ejected from a slowly rotating body and the ejected body will take the form of two spiral arms.
This theory appears to be reasonable so far as the explanation of the typical spiral form is concerned.
The theory of Jeans
The tidal theory of Jeans offers the most plausible explanation of the remarkable system of the planets and comets which owe allegiance to the sun.
The theory supposes that in the remote past the sun was approached by a larger and more massive star. This star came close enough to exert a great gravitational attraction upon the sun’s gaseous and liquid material, upon which huge tides were raised, and a portion being torn from the sun broke up into drops which condensed to the liquid and solid worlds we know. Thereafter the sun’s gravitational attraction held elliptical orbits.
Jeans has shown mathematically that the masses of the planets are just what would be expected from a parent of the size of the sun; and that their relative bulks, forming a cigar shape if jointed up ranging from small to large and down to small again are the natural result of such and origin. He has also shown that the orbits are all the newly born offspring must have been very elliptical at first, just like those of the comets but that frictions, due to much interfering spray, would tend to cause the orbits to cause the orbits to rise to the solar system, must be a comparatively rare occurrence in the universe, and it had been estimated by astronomers that ours took place some 3,000 – 5,000 million years ago.
There are many more theories put forward to account for the origin of the solar system but they do not appear to be quite plausible