The Solar System

The Solar System 

Solar System

 The Solar System: A General Survey

At night you can see very many stars in the sky. But during the day, only one star is .visible, and that is the Sun. This is not because there is anything extraordinary about it but because it is the star closest to us. The light of the other, more distant stars is too feeble to be seen during the day time. The Sun's apparent magnificence had led ancient civilisations to think of it as the 'head' of the universe. Actually, it is only the 'head' of its own family, known as the Solar System. This family consists of :line planets, including the Earth, their satellites, asteroids and comets. Arranged according to their increasing distance from the Sun, the nine planets which go around the Sun are:

Mercury (Buddha), Venus (Shukra), Earth (Prithvi), Mars (Mangal), Jupiter ('Brihaspati), Saturn (Shani), Uranus (Arun), Neptune ( Varun), and Pluto ( Yama),
 Except for Mercury and Venus, all the planets have big and small satellites going around them. There are also countless asteroids and comets in orbit around the Sun.

 All the planets and asteroids, and some comets, revolve around the Sun in elliptical orbits. They all orbit the Sun in nearly the same plane. you can intake a fairly accurate model of the Solar System from a single piece of cardboard on which you can draw the planetary orbits.The only exception of this model is the orbit of. - Pluto, which is inclined at an approximate angle of -17'' to the general plane of the Solar System. The North Pole of the Earth determines the 'north side' of the Solar System. Seen from the "north side", all planets revolve around the Sun. Its gravitational attraction keeps them revolving in their orbits. If the Sun were to suddenly vanish, the planets would all fly off in straight lines at a tangent to their orbits,

The Sun is the dominating member of the Solar System. With a mass calculated to be approximately 2 X 10*30g (grams), it contains almost 99.87% of the mass of the entire  Solar System. Of the nine planets, Jupiter and Saturn are the most massive, accounting for 92% of the mass of all planets. The planets do no generate their own light, like the Sun does. They shine by reflecting the Sun's light that falls on them. The percentage of sunlight reflected by any object is directly related to the amount and type of atmosphere that it possesses. Planets or satellites with no atmosphere, such as Mercury and Moon reflect less light. The moon appears so bright to because of its nearness to the earth.

Sun

All planets, except Venus and Uranus, rotate on their axes in the anticlockwise direction. So, on all these, like on the Earth, the Sun rises in the east and sets in the west. Venus and Uranus rotate in a clockwise direction and as a result, on these two planets the Sun rises in the west and sets in the east! All planets except Uranus have their axes of rotations more or less perpendicular to the plane of orbits. The axis of rotation of Uranus is in its orbital plane, as though Uranus had toppled over.

The four planets, Mercury,  Venus,  Earth and  Mars  are  known as the inner or terrestrial (ie., earth-like) planets. Jupiter, Saturn. Uranus, Neptune, and Pluto are the outer or Jovian (i.e., Jupiter-like) planets. There is a clear division in the properties of the inner and the outer planets. The inner planets consist mostly of metals and rocks and have an average density of 4 or 5 g/cm3 (read as grams per cubic centimetre). The,asteroids.are also like the inner planets in composition. The outer planets, on the other hand, are mostly gas and ice with an average density of or 2 g1 /cm3.

The Sun, A Model Star

The Sun is the most important star from our point of view. It is the only star close enough to be studied in considerable detail. The grandeur of the Sun is partly because of its size. Its diameter is almost 110 times that of the Earth. We can best visualise the volume of the Sun if we realise that more than a million earths can be dropped into the space it occupies. As we have said above, the mass of the Sun is about 2 X 10*30 grams, which makes it more than 300,000 times the mass of the Earth. The average density of the Sun, i.e.. its mass per unit volume, is about 1.4 g/cm3.

Although the Sun appears to be unchanging, it rotates about its axis once every 25 days. From time to time dark patches appear on the surface of the Sun, usually in pairs or in groups. These dark patches are called sunspots. Their movement is an indication of the Sun's rotation. This fact was recognised for the first time by Galileo. Actually, a sun spot is a region on the surface of the S& that consists of gases almost 1000" C cooler than those surrounding the area . The number of sunspots increases and decreases in a cycle every 11 years. In the long term, there are periods of low number of sunspots and High'number of sunspots.

Layers of the Sun

The Sun's body is made up of several layer. The layer that forms the viable surface of the Sun is called the photogphere it is the surface that demarcates Lady oi the Sun and its atmosphere. When we talk of the diameter of the Sun, we are referring-to the diameter of the photosphere. The temperature of the photosphere is about 6000°C. The innermost layer of the Sun is its core where its energy is produced through nuclear reactions. There are other layers between the core and the photosphere which we will not describe here.

Layers of Sun

Like the Sun's body, the solar atmosphere too has several layers. The outermost layer of the Sun's atmosphere is called the corona. Normally, the corona cannot be s&n due I to the brilliance of the photosphere. However, if it is seen during a total solar eclipse, it is visible in its full . The corona extends all the way upto the Earth's orbit and even beyond.

Solar Wind and Solar Flare

Most of the Sun's family is continually bathed in an outflow of material from the Sun's atmosphere. Streams of electrons and protons continuously flow out from the Sun's atmosphere and travel across the Solar System. This rapidly moving stream of charged particles is called the solar wind. About one million ton material is removed every second from the Sun in the form of the solar wind. These charged particles react with the atoms of the Earth's atmosphere to produce northern lights, 'aurora borealis' at the North Pole and southern lights, 'aurora australis' at the South pole: This display of lights in nature, is truly spectacular

Solar Flare

The solar flare represents the most dynamic activity associated with the Sun's surface and atmosphere. It represents a tremendous release of energy in a very short time. Usually it occurs in the neighbourhood of a sunspot. There is a sudden brightening accompanied by a violent outflow of energy in the form of light, radiowaves, X-rays and solar material like electrons and protons.
The Sun is our nearest star and we have been able to examine it quite closely. We have just presented some salient features of the Sun's structure and its activity.

The Earth - The Most Familiar Planet

How do we describe the 'big ball' on which we live? Seen from space, it appears as a bluish-white sphere. Its wealth of plant and animal life, snow covered peaks, blue oceans and white clouds make the Earth a beautiful planet. Human beings have explored it extensively. Yet, the first hand knowledge of the Earth is limited to a thin shell of rock and water extending to a few kilometres below the surface, and to the atmosphere above. However, using indirect methods, such as the study of waves generated during earthquakes, scientists have been able to picture the Earth's interior. without ever seeing or sampling it. We will now briefly describe the current scientific knowledge about the Earth.

The Earth's atmosphere has been studied extensively with the help of ground based experiments, aircraft, rockets and balloons. Though it is not divided into distinct layers, it-is helpful to think of the atmosphere in this way. The troposphere, nearest to the surface, is made up of 78% nitrogen and 21% oxygen, with water vapour, carbon dioxide, neon and argon making up most of the remaining one per cent. It has an average temperature of about 16°C at sea level and- 16 C near its top. The stratosphere, coming next contains ozone and has a temperature ranging from - 16 C to -4C. This ozone layer absorbs the harmful UV radiations fron, the Sun, thus protecting us from them. The carbon dioxide in the Earth's atmosphere traps heat and makes it warmer through the greenhouse effect . Were it not for this, the Earth's surface temperature would be much lower and it would always be covered with ice.

Earth

We will now describe, in brief, the Earth's own structure and composition. Its crust is about 10 km thick under the oceans and about 65 km thick under the continents. If you imagined the Earth to be apple sized, its crust would be as thick as the apple's skin, The main elements in the crust are oxygen (47.3%) and silicon (27.7%). Elements such as aluminium, iron, calcium, sodium, potassium and magnesium make up about 23%, with less than 2% being made up of all other elements.
Crust is the top most part of a layer called lithosphere, the Earth's outer layer. The lithosphere has lumps which we see as mountains, and wrinkles in the form of trenches in the ocean. Beneath the crust, the bulk of the Earth's interior is hot and partially molten

Let us briefly discuss our day-to-day experiences on the Earth, for example, the Earth's rotation on its axis, once every 24 hours, gives it a 24 hours day and night. The regular seasons on the Earth result from the fact, that the Earth's axis of rotation is tilted at an angle to the normal. If it were almost along the normal, like the axis of rotation of some other planets, there would be no seasonal changes on the Earth . The Earth's rotation on its axis and revolution around the Sun makes it  appear as if the Sun, stars and planets were moving in the sky Then there are phenomena like tides in the sea or ocean, and solar and lunar eclipses . These are caused by the presence of me Moon, a satellite of the Earth. kt's find our-more about the Moon.

The Moon, the Earth's Companion

What do you normally observe about the Moon? It shines brightest, whenever present in the night sky. It seems to go through phases and it seems to present the same side toward the Earth always. Let's first explain these observations. The Moon appears to be the brightest night object, because it is the nearest to the Earth. Its phases occur because of its revolution around the Earth. It revolves in an elliptical orbit round the Earth, once in 27.33 days. In the same time, it rotates once on its axis. Thus, we always see the same face of the Moon from the Earth

The Moon is the only other heavenly body on which human beings have landed. They have spent only a short period, though, a total of only 13 days. They brought back samples of lunar rock and soil and much more information about the Moon which we'll briefly describe. The Moon's surface has flat dark expanses called maria (seas), big and small craters,,mountains and-valleys. It also has rilles, i.e., channels such as the ones made on.the Earth by the cutting action of water in a river bed. There are also dome-like structures made of concentric mountain rings.

Earth and Moon

The Moon rocks and soil are almost similar to the earth rocks and soil. However, they are older and contain much higher levels of some elements like titanium and lack elements like sodium and potassium. The lunar soil has the texture of fine damp sand. Unlike its face, the far side of the Moon has no seas, mountains or valleys . It has only uniformly distributed craters. The temperature of the Moon ranges from 130°C in areas directly under the Sun, to - 170°C on its night side. It has neither water nor any atmosphere. About three billion years ago the Moon's interior 'cooled. Since then, it has changed very little and has settled down to a quiet existence.

Formation of  The Solar System

This theory is based on the assumption that the Sun and all the planets were formed from a huge rotating cloud of interstellar gas and dust . For some  reasons, the cloud started contracting. The contraction was hastened by its gravitational  pull. Thee cloud continued to contract. It also started rotating faster and became disc shaped. More and more'matter contracted towards the centre of the disc, forming the star to be-the new Sun. The temperature of this star rose due to contraction until it started generating its own energy . Revolving around the Sun was a disc of gas and dust from which the planets condensed. In this revolving disc, the lighter elements were thrown towards the periphery and heavier elements concentrated inwards. As the Sun's energy increased, the gas shells around the inner planets were driven off and only cores of heavier elements in the cloud remained . The outer planets were less affected. Finally, the bright star's radiation removed the last of the system's free gases and a mixed array of planets remained . The smaller, solid ones were near the star and the much larger gaseous ones farther away. The Earth was the third planet.

Formation of The Solar System

The Early History of the Earth

The Earth has been evolving and changing ever since its origin, about 4.5 billion years ago. In the first tens of millions of years of the Earth's evolution, the impact of small bodies, gravitation, squeezing together of matter and some other factors heated it. This caused some of its constituents to melt. Iron melted before most of the silicates. Since it was heavier it tended to sink toward the centre, forcing up the Lighter silicates towards the surface, just as hot air rises over a stove. As the iron descended, the Earths surface heaved and huge bubbles formed, with volcanoes exploding through it and lava flowing over large parts of it. There were violent storms too. At last most of the iron reached the centre, where it accumulated as the core. Slowly, the Earth cooled and quietened down. Then, a thin shell of solid rock was formed on its surface. The rock shell accumulated as the initial continents at the top of [he lithosphere, like huge rafts. These initial continents drifted about for billions of years. Scientists believe that they formed a supercontinent, which, about 200 million years ago began to drift apart to become the present continents.

The Early History of the Earth

The Sun's radiation had removed the gases from the Earth's surface, so the early Earth had no atmosphere. Water vapour, carbon dioxide, methane and ammonia were released from the molten mass and volcanic eruption and they formed the initial atmosphere. The UV rays from the Sun broke up water into its constituents, hydrogen and oxygen. Being a light gas, hydrogen escaped from the Earth. Oxygen combined  with ammonia and methane to form water, nitrogen, carbon dioxide and other compounds. Higher up three atoms of oxygen combined to form ozone molecules and so the ozone layer was formed at the same time. As the Earth cooled further, water vapour in the atmosphere became condensed, and it fell as rain to fill the huge craters on the Earth.

About four billion years ago, a much more remarkable process began on the Earth. This was the first feeble start of life. Paradoxically, the same UV rays that would kill most modern creatures today, helped the beginnings of life.  The Earth has a special relationship with the Sun. Life on Earth would not have survived, but for the Sun It is a steady source of energy tor all basic processes that sustain life. Also the Earth's distance from the Sun is such as to produce a climate that was and still is quite mild, conducive to our kind of life

Old Earth to New Earth

So far we have discussed various features of the Sun, the planets and their satellites, asteroids and comets, and the formation of the Solar System. It is appropriate that we now analyse some myths and misconceptions associated with their influence on our lives.

Some Myths and Misconceptions

Out of this wrong, but natural conviction grew astrology. The idea started developing that a person's future was determined by which constellations the planets were in at the moment of his or her birth. The motion of the planets was believed to determine the fates of kings, dynasties and empires. Astrologers studied the motion of planets accurately. They would know what had happened, the last time that, say, Mars was rising in the Constellation of the Lion. Perhaps a similar thing would happen again. And, thus, they would tell kings when to attack a neighbouring state. If the position of thc 'war gods' Saturn and Mars were 'unfavourable', they might advise the king to postpone his campaign. A good way to overthrow a regime was to predict its downfall! And if planets could determine the fate of nations, they could also influence the events in a person's life. Thus, astrology grew into a strange combination of observations and mathematics, with illogical thinking. Nevertheless, with time, astrologers came to be patronised by the State. This led to an increase in the influence of 'astrology, which continues to this day all over the world. But a precise cause and effect relationship between the movements of planets and human beings has never been scientifically established. In fact a critical analysis of astrological beliefs would show you that they re totally unscientific; they can be disproved in the light of the day to day events.