Cosmos” is just another word for universe, and “cosmology” is the study of the origin, evolution and fate of the universe. Some of the best minds in history – both philosophers and scientists – have applied themselves to an understanding of just what the universe is and where it came from, suggesting in the process a bewildering variety of theories and ideas, from the Cosmic Egg to the Big Bang and beyond.

The most popular theory of our universe’s origin centers on a cosmic cataclysm unmatched in all of history—the big bang. This theory was born of the observation that other galaxies are moving away from our own at great speed, in all directions, as if they had all been propelled by an ancient explosive force.

Our universe is both ancient and vast, and expanding out farther and faster every day. This accelerating universe, the dark energy that seems to be behind it, and other puzzles like the exact nature of the Big Bang and the early evolution of the universe are among the great puzzles of cosmology.


Theories of the universe

Where did the Earth come from? This is an important question. A question that helps us understand our own origin as a race of sentient, thinking beings. Did the Earth always exist? Has our planet spent eternity orbiting the Sun, quietly unchanging? Has the Earth always looked like it does today, with the same mountains, streams, lakes, forests, and oceans? Or does the Earth change over time? Was the Earth always a planet, or was it built or constructed at some point in the past? If it was built, what forces caused its creation, and from where did the materials to build it come?

These are difficult questions to answer. The Earth is our home world. Before the Earth existed, there were no people. This means that there was no one around to witness its creation. At least not any humans. However, scientists, like geographers, are able to make educated guesses about how the Earth came to be. These guesses are called theories. A theory is a guess based on evidence. These guesses are made by scientists who study clues to understand new things about the world and universe around us.


There are only two legitimate options for the origin of the universe:

  1. Someone made the universe ( Intelligent Design )
  2. The universe made itself ( Random Chance ).

In general, theists attribute the origin of the universe, to some sort of transcendent, intelligent Designer. Atheists envision a natural, undirected process by which Universes spring into existence spontaneously.

Einstein’s theory of gravity and Hubble’s astronomical observations preclude an eternal universe. We now know beyond a reasonable doubt that the universe began at some point in the finite past.


Big Bang Theory

Georges Lemaitre (1927) had proposed a model for origin of the universe which became the Big Bang theory. The Big Bang theory explains the origin of universe, with the key idea that the universe is expanding. In the past, the universe was denser and hotter. All of space was contained in a single point, which is considered the inception of the universe. After the initial expansion, the universe freezes that allowed the creation of subatomic particles, consisting of protons, neutrons, and electrons. The majority of atoms formed were hydrogen, along with helium and traces of lithium. Huge clouds of these primal elements later fused through gravity to form stars and galaxies. The massive elements were synthesized either within stars or during supernova. Hence, the Big Bang theory does not explain the initial condition of the universe, but instead it describes the general evolution of the universe.

The Big Bang theory is based on Albert Einstein’s theory of general relativity. This also takes into consideration the homogeneity and isotropy of space. It was Edwin Hubble (1929), who discovered that the distances to remote galaxies were firmly correlated with their redshifts. According to Hubble, all observable areas of the universe are receding from each other.

Once there were two theories for explaining the expansion of universe, the Big Bang and the Steady State theory. But in 1964, with the discovery of the cosmic microwave background radiation, the Big Bang theory was confirmed.

In 1992, the launching of the Cosmic Background Explorer (COBE) satellite showed that 99.7% of the energy of the universe was released within the first year of its evolution. This confirmed the Big Bang theory, which proposes that the universe originated from a single violent explosion (which gives the name big bang) of a very minute amount of matter of high density and temperature.

The Moments after the Big Bang

The very early universe (at a time a few fractions of a second after the Big Bang began) was not bound by the laws of physics as we know them today. So, no one can predict with great accuracy what it looked like at that time. Yet, scientists have been able to construct an approximate representation of how the universe evolved.

First, the infant universe was initially so hot and dense that even elementary particles such as protons and neutrons could not exist. Instead, different types of matter (called matter and anti-matter) collided together, creating pure energy. As the universe began to cool during the first few minutes, protons and neutrons began to form. Slowly, protons, neutrons, and electrons came together to form hydrogen and small amounts of helium. During the billions of years that followed, stars, planets, and galaxies formed to create the current universe.


Inflation Universe Theories

The original big bang theory is no longer the dominant scientific explanation for the atheistic origin of the universe.

Starting with Alan Guth in the late 1990’s ( The Infla – tionary Universe :  The Quest for a New Theory of Cosmic Origins ), the scientific community has now proposed roughly 50 different IUT variants.

The Inflation Theory, developed by Alan Guth, Andrei Linde, Paul Steinhardt, and Andy Albrecht, proposes a period of extremely rapid ( exponential ) expansion of the universe leading to the Big Bang expansion, during which time the energy density of the universe was dominated by a cosmological constant term that later decayed to produce the matter and radiation that fill the universe today.

The Inflation Theory links important ideas in modern physics, such as symmetry breaking and phase transitions, to cosmology.


String Theory

In the last few decades, string theory has emerged as the most promising candidate for a microscopic theory of gravity. It attempts to provide a complete, unified, and consistent description of the fundamental structure of our universe.

String theory suggests that the big bang was not the origin of the universe but simply the outcome of a pre – existing state.

Our current knowledge about the subatomic composition of the universe is summarized in what is known as the Standard Model of particle physics.

It describes both the fundamental building blocks out of which the world is made, and the forces through which these blocks interact.

There are twelve basic building blocks. Six of these are quarks – having the interesting names of up, down, charm, strange, bottom and top. ( A proton, for instance, is made of two up quarks and one down quark. ) The other six are leptons – these include the electron and its two heavier siblings, the muon and the tauon, as well as three neutrinos.

The essential idea behind string theory is this all of the different fundamental’ particles of the Standard Model are really just different manifestations of one basic object – a string. Ordinarily, an electron is picturised as a point with no internal structure.

A point cannot do anything but move. But, if string theory is correct, then under an extremely powerful ‘microscope’ we would realize that the electron is not really a point, but a tiny loop of string.

A string can do something extra than moving – it can oscillate in different ways ( like a guitar string ). If it oscillates in a certain way, then from a distance; unable to tell that it is really a string, we see an electron. But if it oscillates in some other way, we call it a photon, or a quark, or something else. So if string theory is correct, the entire world is made of strings.


Universe New Theory

A New Zealand theorist, Peter Lynds, presented his second paper on the theory of origin of universe on 1 November 2007, and has suggested that time is ‘cyclic’.
Thus, the universe’s clock has neither a start nor finish, yet time is finite. The cyclic view of time was also held by ancient thinkers such as Plato, Aristotle and Leonardo da Vinci.
However, the Christianity and the Church established the view of time being linear and going in a straight line.
Lynds’ theory involves the second law of thermo-dynamics. All of the laws of physics – with the exception of the second law of thermodynamics – are time reversible and work equally well in opposing directions.
This is in contrast to previous theories involving thermodynamic time reversed, including those by Thomas Gold in the 1960s and Stephen Hawking in the 1980s, which all involve the second law of thermodynamics being breached.
Such theories have generally been dismissed by physicists because of contradictions directly resulting from such a second law violation.
Lynds asserts that if many billions of years from now the universe stops expanding and contracts to a big crunch, such a revised conception of thermodynamic time reversal leads to a coherent picture of the cosmos in which there is no differentiation between past and future, and the so called beginning of the universe, the big bang, can equally be said to be in the past or future of the big crunch.
This means that the big bang’ and the big crunch can also equally be said to cause one another, therefore providing an answer to that most intractable of questions : what caused the big bang?’ His theory asserts that the universe is finite, but yet also has no beginning or first cause ( because the big bang is caused by the big crunch, and the big crunch is caused by the big bang, in a cyclical occurence ).
Cosmogony, or cosmogeny, is any theory concerning the coming into existence or origin of the universe. Cosmogony can be distinguished from cosmology, which studies the universe at large and throughout its existence, and which technically does not inquire directly into the source of its origins.
The difference between space and outer space is that space means the whole universe including the earth while outer space means all space other than earth. In fact, outer space begins where the earth’s atmosphere ends and extends on and on in all directions.


Asteroid Belt

The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter.

It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt region is also termed the main belt to distinguish it from other concentrations of minor planets within the Solar System, such as the Kuiper belt and scattered disk.

Asteroids: Asteroids are small bodies that are believed to be left over from the beginning of the solar system 4.6 billion years ago. They are rocky objects with round or irregular shapes up to several hundred km across, but most are much smaller.

Meteors : Meteors are streaks of light, usually lasting just a few seconds, which people occasionally see in the night sky.

They are sometimes called ‘shooting stars or ‘falling stars’, though they are not stars at all. Meteors are caused by the entry of small pieces of rock, dust, or metal from space into the atmosphere at extremely high speeds.

These particles are called ‘meteoroids’ when they are floating around in space. The incredible pressure meteoroids experience when they collide with Earth’s atmosphere shatters them, transferring energy to atoms and molecules in the atmosphere, which then release the energy by glowing. This glow produces the bright trails of light in the sky we see as meteors. Very rarefy, a larger meteoroid actually survives to strike the ground. These chunks of rock or metal are called “meteorites’.


The Milky Way

The Milky Way is our galaxy, Le., it is the home of our Solar System together with at least 200 billion other stars ( more recent estimates have given numbers around 400 billion ) and their planets, and thousands of clusters and nebulae, including at least almost all objects of Messier’s catalog which are not galaxies on their own.
Light year : The Light year is a measure of distance not time. It is the distance that light travels in a vaccuum in one year at the speed of 300,000 km / s or 186,000 miles per second. In one year, at that speed, light travels approximately 6 million miles or around 9.5 trillion kilometres. Light travels one Astronomical Unit ( AU ) in only 8 minutes.
Astronomical unit : We classify distances in space according to the mean distance between the sun and the earth, which is one AU. One AU is equal to 93 million miles or 150 million kilometers. So that means the sun is 93 million miles away from Earth. Light travels this distance in 8.3 min approx. 9.
Messier’s catalog : During the years from 1758 to 1782 Charles Messier, a French astronomer ( 1730 -1817 ), compiled a list of approximately 100 diffuse objects that were difficult to distinguish from comet through the telescopes of the day. Discovering comets was the way to make a name in astronomy in the 18th century. Messier’s first aim was to catalog the objects that were often mistaken for comets.



Not all comets have tails.

The tails takes shape only when the comet gets close to the sun.

Comet tails always point away from the sun because of the force exerted by solar wind and radiation on the cometary material.

The period of Encke’s comet is only 3.3 years, Halley’s comet – 76 years, Hale -Bopp is about 4000 years, and Kohoutek’s comet is about 75,000 years.

Comets are lumps of ice and dust that periodically come into the center of the solar system from somewhere in its outer reaches. When comets get close enough to the Sun, heat makes them start to evaporate. Jets of gas and dust form long tails that we can see from Earth.

The comets that pass close to the Sun originally came from one of two places : either the Oort Cloud or the Kuiper Belt.

The Kuiper Belt : The Kuiper belt is the most recently observed section of the Solar System. The Kuiper belt extends from Neptune’s orbit to three billion kilometers beyond it. It contains lumps of icy material with organic compounds. That makes them like comets. These lumps are called Kuiper belt objects or minor planets.

The Oort Cloud : A vast cloud exists at the outer reaches of the solar system. This has come known as the Oort Cloud.



A galaxy is a huge collection of gas, dust and billions of stars held together by their mutual gravity. Almost all the galaxies display red shift in their spectra indicating they are moving from us.
There are an estimated 50 thousand million galaxies in the universe, and a typical galaxy contains 50 thousand million to 100 thousand million stars.
Our sun and the surrounding planets orbit around the center of the Milky Way galaxy once every 250 million years.
The Local Group of Galaxies : This is our group of galaxies. It was first recognized by Hubble, at the time of the first distance determinations and red – shift measurements.


Andromeda Galaxy

Andromeda is the nearest major galaxy to our own Milky Way Galaxy. It j is a large spiral galaxy, very similar in appearance to, and slightly larger than, our own Galaxy, and our closest normal galaxy companion ( the very dose Magellanic clouds are classified as irregular galaxies ).
The farthest one can see with the naked eye is 2.4 million light years away or ( 140,000,000, 000,000,000, 000 miles. ) That’s the distance to the giant Androm – edii Galaxy.
The light arriving at earth from the Andromeda Galaxy is shifted toward the blue end of the spectrum, whereas the light from all other cosmic sources exhibits red shift.
Magellanic Clouds : The two Magellanic Clouds ( Large Magellanic Cloud and Small Magellenic Cloud ) are irregular dwarf galaxies, which are members of our Local Group of galaxies.
Geography Types of Galaxies

Three main classes of galaxy were originally described by Edwin Hubble in his 1936 work, The Realm of the Nebulae – ellipticals, lenticulars and spirals – based on their visual appearance ( originally on photographic plates ). A fourth class contains galaxies with an irregular appearance.
Spiral Galaxy : Spiral galaxies consist of a flat, rotating disk of stars, gas and dust, and a central concentration of stars known as the nuclear bulge. These are surrounded by a much fainter halo of stars, many of which reside in globular dusters.
Elliptical Galaxy : Elliptical galaxies have smooth, featureless and light profiles and range in shape from nearly spherical to highly flattened, and in size from hundreds of millions to over one trillion stars.
Lenticular galaxy : It is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disc galaxies ( like spiral galaxies ) which have used up or lost their interstellar matter ( like elliptical galaxies ). Because of their ill – defined spiral arms, if they are inclined face – on, it is often difficult to distinguish between them and elliptical galaxies.
Irregular galaxy : A galaxy that does not fall into any of the regular classes of the Hubble sequence. These are galaxies that feature neither spiral nor elliptical morphology. They are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.
The Hubble sequence : It is a morphological classification scheme for galaxies invented by Edwin Hubble in 1936. To this day, the Hubble sequence is the most commonly used system for classifying galaxies, both in professional astronomical research and in amateur astronomy.



A theoretical shortcut through space caused when a black hole punches through the fabric of spacetime. While possible mathematically, in reality they probably do not exist.



A constellation is anyone of the 88 areas into which the sky – or the celestial sphere is divided. The term is also traditionally and less formally used to denote a group of stars visibly related to each other in a particular configuration or pattern.

Some well – known – constellations contain striking and familiar patterns of bright stars. Examples are Orion ( containing a figure of a hunter ), Leo ( containing bright stars outlining the form of a lion ), Scorpius ( a scorpion ), and Crux ( a cross ).


Black Hole

John Wheeler, a US Physicist, first used the term ‘black hole’ for a completely collapsed star at a meeting at the Institute for Space, New York, in 1967.

The nearest known black hole is 1,600 light years ( 10 quadrillion miles / 16 quadrillion kilometers ) away.

Black holes may not be totally black. Infalling material can get hot enough to glow.

Sometimes black holes are so bright they can out-shine an entire galaxy.

A black hole is a region of space in which the gravitational field is so powerful that nothing can escape after having fallen past the event horizon.

The name comes from the fact that even electro – magnetic radiation ( e.g. light ) is unable to escape, rendering the interior invisible.

However, black holes can be detected if they interact with matter outside the event horizon, for example by drawing in gas from an orbiting star.

While the idea of an object with gravity strong enough to prevent light from escaping was proposed in the 18th century, black holes, as presently understood, are described by Einstein’s theory of general relativity, developed in 1916.

This theory predicts that when a large enough amount of mass is present within a sufficiently small region of space, all paths through space are warped inwards towards the center of the volume, forcing all matter and radiation to fall inward.

Event horizon : In general relativity, event horizon is a general term for a boundary in spacetime, an area surrounding the black hole, beyond which events cannot affect an outside observer. Light emitted from inside the horizon can never reach the observer and anything that passes through the horizon from the observer’s side is never seen again.

Escape velocity is the velocity needed for an object to become essentially free of the gravitational effect of another object. Thus, event horizon can also be defined as the distance from the center of a black hole where the escape velocity is equal to the speed of light.


Birth of a Star

Nebulae : It is the plural of nebula, which means an interstellar cloud of dust, hydrogen gas and plasma. It is the first stage of a star’s cycle. These young stars undergo further collapse, forming main se – Ili quence stars.

Orion Nebula : The Orion Nebula ( also known as Messier 42, M42, or NGC 1976 ) is a diffuse nebula situated south of Orion’s Belt. It is one of the brightest nebulae, and is visible to the naked eye in the night sky.

Protostar : Stars are born in nebulae. Later, huge clouds of dust and gas collapse under gravitational forces, forming protostars. For a solar – mass star, the protostar stage lasts about 100,000 years. It starts with a core of increased density in a molecular cloud and ends with the formation of a Tauri star, which then develops into a main sequence star. This is her aided by the T Tauri wind, a type of ‘Super solar wind that marks the change from the star accreting mass into radiating energy.

Red giant : Stars expand as they grow old. As the core runs out of hydrogen and then helium, the core contacts and the outer layers expand, cool, and become less bright. This is a red giant or a red super giant ( depending on the initial mass of the star ). It will eventually collapse and explode. Its fate is determined by the original mass of the star.

It will become either a black dwarf, a neutron star, or a black hole. A red giant is a luminous giant star of low or intermediate mass that is in a later phase of its evolution, with nuclear fusion going on in a shell outside the core but not in the core itself.


Lifecycle of a Star

There are three possibilities, based on the initialass of the star.

  1. Stellar nursery ( stars form in a nebula, from collapsing clouds of interstellar gas and dust ). 2. Sunlike stars ( up to 1.5 times the mass of the Sun ). 3. Red giant. 4. Planetary nebula: 5. White dwarf. 6. Black dwarf.
  2. Stellar nursery ( stars form in a nebula, from collapsing clouds of interstellar gas and dust ). 2. Huge stars ( from 1.5 to 3 times the mass of the Sun ). 3. Red supergiant. 4. Supernova. 5. Neutron star.
  3. Stellar nursery ( stars form in a nebula, from collapsing clouds of interstellar gas and dust ). 2. Giant stars ( over 3 times the mass of the Sun ). 3. Red supergiant. 4. Supernova. 5. Black hole.


Death of a Star

Planetary Nebula : A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. The name originates from a similarity in appearance to giant planets when viewed through a small optical telescope, and is unrelated to planets of the solar system.

Supernova : It is a stellar explosion. After the core of an aging massive star ceases to generate energy frol} 1 nuclear fusion, it may undergo sudden gravitational collapse into a neutron star or black hole, releasing gravitational potential energy that heats and expels the star’s outer layers.

Alternatively, a white dwarf star may accumulate sufficient material from a stellar companion to raise its core temperature enough to ignite carbon fusion, at which point it undergoes runaway nuclear fusion, completely disrupting it.

Stellar cores whose furnaces have permanently gone out, collapse when their masses exceed the Chandrasekhar limit ( roughly 1.38 times the mass of the Sun ). The material that is exploded away from the star is now known as a supernova remnant.

White Dwarf : It is a tiny, dense, hot star, representing, a late stage in the life of a star like the sun. The core of a very hot young white dwarf cools down over the course of the next billion years or so. Many nearby, young white dwarfs have been detected as sources of soft ( Le. lower – energy ) X – rays.

Black Dwarf : It is a tiny blackened corpse of a star like the sun. Ultimately it disappears into the blackness of space.

Neutron star : A neutron star is formed from the collapsed remnant of a massive star after supernova. Models predict that it consists mostly of neutrons. A neutron star is one of the few possible conclusions of stellar evolution.

Chandrasekhar limit : The Chandrasekhar limit named after Subrahmanyan Chandrasekhar  is the maximum non – rotating mass which can be supported against gravitational collapse, by electron, degeneracy pressure.



Pulsars are highly magnetized rotating neutron stars which emit a beam of detectable electromagnetic radiation in the form of radio waves. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the light – house effect and gives rise to the pulsed nature that gives pulsars their name.

Because neutron stars are very dense objects, the rotation period and thus the interval between observed pulses are very regular. For some pulsars, the regularity of pulsation is as accurate as an atomic clock. Pulsars are known to have planets orbiting them.

Variable star: are stars that show varing degree of luminosity. Delta cephei was the first of this type of stars noticed in 1784 by the deaf and dumb English astronomer John Goodriche.



A Quasar is an enormously bright object at the edge of our universe with the appearance of a star when viewed through a telescope. It emits massive amounts of energy, more energy than 100 normal galaxies combined.

The name comes from a shortening of quasi stellar sources of radio radiations. Current theories hold that quasars are one type of active galactic nuclei ( AGN ).

Many astronomers believe supermassive black holes may lie at the center of these galaxies and power their explosive energy output. In one second, a typical quasar releases enough energy to satisfy the electrical energy needs of Earth for the next billion years.

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