Astronomy is an ancient science which has fascinated mandkind from early times. Its contributions to the development of scientific thought have been immense.
Our planet mother earth, the third planet in the solar system which seems so significant to us floats in space like a small ball. From our small world let us look outward into the vast ever expanding universe.
For generations human beings have been observing the sky. These observations and finding s have given us an opportunity to unravel some of the mysteries of the universe. Through this article i will take you to a journey through space and time and will introduce theuniverse to you. The universe filled with stars, galaxies and nebulae.
W will start our journey from the birth of our Universe then well go to the galaxies, birth, life and death of stars and then we will return oto our solar system with the knowledge of our origin and our link with the Universe.
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Astronomy has changed a lot during the last 40 years. Today it has become as part of our everyday life, satellites are circling the earth and space probes have been sent out to teh planets.In the olden days our ancestors could know the time by looking at the stars and could also define and use directions by looking at the stars.
In the past 4 decades there have been 2 main theories attempting to explain the evolution of the universe. One of them is the Steady State Theory, which states that the universe has neither beginning nor end, and will continue in the same state as of the present for ever.
A second theroy is called the Bg-Bang theory. According to thsi theory asll the matter in the universe was once contained in dense and hot fire ball. This fire ball suddenly exploded throwing out all the matter. This matter chiefly consisted of hot radiation and particles. Gradually the matter cooled down giving rise to primeval clouds of gas. later on tehy evolved into moare compact blobs of gas and out of which stars, planets, galaxies and all the matter that we see in the universe came into being.
Nebula plural is nebulae is alatin word which means cloud. This is not the same cloud, which gives us rain but it chiefly consists of hydrogen gas and interstellar sdust. Here stars are born. In other words we can say that the nebulae are the birth place of stars. Our Sun Was also born from one such nebula, about the billionj years ago.
Orion Nebula :
The well known orion nebula is in the constellation orion and can be seen in the winer sky with a powerful telescope. Dotted among the gas and dust are very hot young stars. One such group of strs, teh trapezium, is seen at the base of the Nebula. This Nebula is the birth place of stars. There is another nebula in orion, Nicknamed the horse head nebula it is also a birth place of stars. it is called horse head nebula because of its appearance.
Crab Nebula :
The crab nebula in the taurus constellation, is also a gas cloud tells you a different story but is quite different from teh orion nebula. It represents the end of a star's life rather than a beginning. In that sense it is the graveyard of a very massive star which died in an explosive death seven thousand years ago.
Ring Nebula :
This is a planetary nebula- a shell of gas, imprisoned among, it is a small hot star. The ring nebula- is visible near the star vega of the lyra constellation. It can be seen with a powerful telescope. Scientists believe that it is also a kind of dead star.
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A galaxy is a collection of several billions of stars, grouped together due to gravitational force and are in mutual gravitational interaction. It also contains huge gaas and dust particles, clouds of interstellar debris and high energy particles known as cosmic rays.
Types of Galaxies :
Our ancient astronomers had no knowledge about the galaxies, their shapes etc. Most of the work was done on the classification and identification of galaxies by teh great american astronomer Edwin Hubble in 1920. Hubble's classification provides four general categories of galaxies. All these major types of galaxies are again divided into subclasses but we will try to understand about 4 general types os galaxies. Hubble classified these galaxies into four groups - Elliptical,Spiral, Irregular and Lenticular.
Lenticular Galaxy :
Have disc like structures without arms but with a prononned center and an extended area around the centre.
Spiral Galaxy :
The third type of galaxies are the spiral galaxies. These galaxies differ considerably from elliptical galaxies both in structure and their stellar content. Thenucleus of these galaxies, resemble and elliptical galaxy but here the similarity between teh two ends. Spiral galaxies posses spiral arms. A spiral arm consists of concentrations of stars dust ana gas.These arms rotate about the galactic nucleus in a pin-wheel fashion taking hundreds of millions of years for one rotation. However, they do not rotate as solid objects but rather they resemble the motion of a thick layer of oil floating on water and being stirred. The stars in these arms do not rotate sall together like a gramophone record. Those near the central region go around the center much more rapidly than those in the outer regions. Spiral galaxies range in size from about 20000 to more than 100000 light years in diamieter. Our milky way galaxy belongs to this category.
Irregular Galaxy :
The least common type of galaxy is the irregular galaxy irregular galaxies are quite different from both the elliptical and spiral galaxies. These show no trace of either circular or rotational dymmetry but instead have anirregular or chaotic appearance. The best known examples are the large and small magellanic clouds, which are satellites of our own galaxy. Let us go into more details of our own galaxy : Milky Way Galaxy.
Milky Way Galaxy : It resembles a smugged pattern of flowing milky inthe sky. Of course It is not visible to the naked eye from cities like bombay due to the haze created by the city lights and industrial pollution. But if you were to go to avillage you can see the milky way with the naked eye. All the stars which we see in the night belong to our own galaxy. Infact the milky way contains more than 200 billion stars and our sun is just an average star, situated two- third away from its centre in one of the spiral arms.
Our Galaxy is so large that light takes about 100000 years to go from its one end to other end ie. the diamieter of our galaxy is one lakh light years.
LIGHT YEAR :
In astronomy, measureing distances in kilometers and meters is inconvinient. Hence a new light year is used. A light year is the distance travelled by light in 1 year in free space. The speed of light is about 3 lakh kilomters per second. At This fantastic speed, light covers the distance of approximately 10 trillion lilomters i.e. one followed by thriteen zeros in one year.
Galaxy is a collection of billions of stars so the question is that what is a star? A star is a celestial object which has its own luminosity. they thake birth,live their lives and die like us humans. However, unlike us their life spans over not hundreds but billions of years.
Birth Of Stars :
Stars from within and from those massive gas clouds- the Nebulae. These clouds are gigantic in size with most of the material being a tenuous mixture of hydrogen, helium and small amount of other heavier elements. A huge cloud of gas in teh interstellar space does not remain stable. teh gs is occasionally subjected to tremendous pressure due to shock waves cased by nearby explosions of stars. Tehis compresses the cloud and splits it into a number of much denser clouds and triggers the formation of stars in the nebula.
As the gas gets denser and denser due to gravity or due to its internal eddies at some stage it begins condensing due to its own gravitational force. Teh cloud starts shrinking by itself. As the dust and gas contract under the pull of their own gravity, the temperature within the nebula.
Teh gravitational energy is being converted and released as heat. The higher the temperature, the faster the motion of particles in teh heart of this cloud. As a result the atoms and molecules of the cloud collide with one another more and more violently. when the temperarture reaches a few thousand degrees celsius, electrons get stripped off from their atoms. Teh hydrogen atom has a single negatively charged electron. When the hydrogen atoms within the interstellar gas cloud are stripped of their orbiting electrons teh protons are free and due to high temperature electrons are highly excited. As the temperature in teh cloud reaches about 10 million dgreees kwlvin, 2 protons on colliding fuse together releasing a positron and neutrino. This fusion of 2 protons results in teh formation of the nucleous of deuterium heavy hydrogen - A nucleus containing a positively charged proton and neutral neutron- the neutron being formed from one of the protons during the fusion reaction. In course of time thsi deuterium nucleus fuses with one more proton and in due course a four proton in absorbed by the nucleus. Teh net result of the process is the formation of nucleus of the atom helium from 4 neucleii of the atom Hydrogen.The fusion reaction is called Thermo-nuclear reaction. Due to this reaction taking place in the cloud energy in the form of light and heat is given out. The outward pressure generated by this newly released energy balances the universal pressure of gravity. The cloud reaches a state of dynamical equilirium and it shines brightly as it becomes stable and gives out heat and light. And we say A star is Born.
Death Of Stars :
Stars convert hydrogen into helium by thermo nucleur reactions. Hence a stage comes in the life of a star when hydrogen is depleted in its core. Much of it has already been converted into helium and releasing energy in the process. Howeversome amount of hydrogen is still leftover in a shell surrounding the core. The fusion reaction continues here and leads to the death of star.
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