THE SUN

Billions of stars are scattered throughout the universe. The one at the center of the solar system plays a special role for us here on Earth.

Our Sun formed about 4.5 billion years ago in the milky way galaxy’s Orion spur. it was born when a cloud of dust and gas known as solar nebulae collapsed. And in the middle of this formation that are condensed in to a burning ball of gas that became our Sun.

The Sun’s fiery nature along with the tremendous gravitational pull and an extensive magnetic field helped it to become the heart of our solar system.

The Sun can be divided  into six layers of regions. The corona, the chromospheres, the photosphere, the convective and radioactive zones and the core. In terms of Adam count, the Sun is about 91% hydrogen: the Sun’s fuel, 8.9% helium and .1% heavier elements such as carbon and nitrogen. Due to the Sun’s extreme temperature, these elements will stay in a gas like state called plasma.

In the core, temperature reaching at least 27 million degrees Fahrenheit. Combined with the Sun’s powerful gravity fused together hydrogen molecules to create helium called thermonuclear fusion. This releases an enormous amount of energy in the form of radiation, electricity, solar wind and as we experience on earth, life giving heat and light.

It is strong enough to hold the solar system  intact and is primarily due to the Sun’s size and mass. Our Sun is the largest and most massive object in the solar system. It is more than hundred Earth’s wide and could theoretically fit all eight planets inside nearly six hundred times. It also contain approximately  99.8% of all the masses in the solar system. Because of this mass, the Sun has a great pull on the fabric of space, creating a gravitational force that causes nearby   planetary bodies to be drawn towards it. This gravitational pull allows the Sun to hold together a system of eight planets, potentially dozens of dwarf planets at least 170 moons and countless comets and asteroids. Without the Sun’s gravity these celestial bodies would drift off into deep space.

Another critical property of Sun is its magnetic field which encapsulate the entire solar system called the heliosphere. This force field protects the planets from harmful cosmic radiations. It is caused by the Sun’s plasma pushing electrically charged particles towards the solar poles. This process turns the Sun in to a giant magnet. Although the Sun’s magnetic field is invisible to the naked eyes, its effects are noticeable. On the Sun’s surface, the dark areas are called Sun spots which marks strong magnetism.

On Earth and on some of the other planets, the Sun’s magnetic field interacts with their atmosphere resulting in beautiful auroras. Despite its size and strength, the Sun will not last forever. In about 6.5 billion years, it will run out of its hydrogen expand to envelop mercury. Then it will collapse in to a small star known as white dwarf.

In the mean time, the Sun will continue to play a critical role in the system  that bears its name. The Sun’s protected magnetic field, tremendous gravitational pull and ability to create vast amount of energy will protect, contain and give life to our solar system.  

THE SOLAR SYSTEM

A star may be defined as a huge, massive body of luminescent matter radiating enormous amount of energy second. Each star holds around itself, under the influence of force of gravity, a variable number of relatively small sized, non-radiant bodies of matter, called planets. The basic difference between the star and planet is in their masses : a star is thousand times bigger than a planet. Because of such an enormous mass very high temperatures are reached inside the star that make it radiate energy. Our sun is also a typical star. It has nine planets held and revolving around it under gravitation. The sun and the planets taken together make a solar system. Each galaxy is believed to contain billions of solar systems. Our solar system_ the sun in the center and the nine planets revolving around it is just an insignificant part of our galaxy, named by us for our convenience, as MILKY WAY.

The nine planets revolving around the sun in order of their increasing distance from the sun have been named as Mercury, Venus, the Earth, mars, Jupiter, Saturn, Uranus, Neptune. The mean distance from the Earth to sun is computed as 149,642,000 km. this distance is commonly referred as One Astronomical Unit. it is very inconvenient to use this unit in describing the distance of other planets from the sun as follows:

S.no	Name	Distance(A.U)	S.no	Name	Distance(A.U)
1.	Mercury	0.39	5.	Jupiter	5.20
2.	Venus	0.72	6.	Saturn	9.54
3.	The Earth	1.00	7.	Uranus	19.20
4.	Mars	1.52	8.	Neptune	30.10

*A.U. =Astronomical unit = 14,96,42,000 km, taken approximately as 150 million kilometres

**Astronomers classify Pluto(38.0 A.U) as a ‘dwarf planet’.

All the nine planets including the earth revolve around the Sun along regular, stable and nearly circular paths called orbits that lie almost in the same plane(except that of  Pluto). The Earth makes its orbital motion around the Sun at a speed of 29.76 km per second and complete one revolution in 365.25 days or one year. For the other 8 planets, the speeds of revolution and  the days they take to complete one revolution are different. All the nine planets also rotate around their own axes in a perpetual manner while revolving around the Sun. The period of rotation around their axes also varies from planet to planet. The Earth, as we know, has period of rotation of 23 hours 56 minutes and 4 seconds. The planet Venus takes the longest time to complete one rotation : 88 days and the planet Jupiter takes the shortest time : 9 hours 50 minutes.

GROUPING OF PLANETS

On the basis of their distance from the Sun and other broad similarities, the nine planets conveniently fall in to two groups.

(a) The inner or terrestrial planets

      Four planets namely Mercury, Venus, the Earth and Mars constitute the terrestrial group. They are characterized with

      (i) relatively smaller masses

     (ii) higher densities

    (iii) slower speed of rotation

(b) The outer planets

       They are also called superior planets and include five members : Jupiter, Saturn, Uranus, Neptune. They are characterized with :

     (i) very large masses

     (ii) much lower densities

    (iii) faster rotation

    (iv) Higher number of satellites

 Moons

Except Mercury and Venus, all the other seven planets have natural satellites called moons revolving around them. The number of moons is different for different planets. Our Earth have one moon where as Mars have two moons as per the information released by planetary society, the number of moons , including ”moonlets” for other planets of solar system as on June 2003 stood as Jupiter (61), Saturn (31), Uranus (21), Neptune (11). These counts are likely to increase with time as more and more discoveries are announced periodically from observatories.

Our moon moves around the earth in an elliptical orbit at a mean distance of 3,83,403 km and a period of 27 days, 7 hours 43 minutes and 11.5 seconds.

Beside the planets and other satellites, our solar system is also populated with a belt of smaller planet- like masses called Asteroids that revolves around the Sun in the space between the orbit of Mars and Jupiter.

 Meteors commonly seen as shooting stars are merely broken fragments of planetary materials that enter in to our atmosphere almost every day. When such a mass of matter happens to enter our atmosphere at night, it meets enormous friction from the atmospheric gases and shines brilliantly for a few moments before it gets completely consumed and dissipated. Occasionally remaining parts of these meteors reach the surface of the Earth and strike with strong impact. These meteors reaching the surface are called Meteorites. Thousand of tones of meteoric material is believed to fall on the surface of the Earth every year. These materials have been extensively studied and grouped in to three categories : stony meteorites, intermediate meteorites, iron meteorites. Many craters(depressions) found on the surface of the Earth are believed to have resulted due to the impacts of meteorites in the recent geological past. Sometimes the meteoric materials can be actually traced near the crater leaving no doubts about its origin.

Comets are yet another group of planet-like masses having very elliptical orbit of motion around the Sun. They appear in the sky as dazzling tailed stars (having tail spread over thousands of kilometres) after regular interval of many years. The famous HAILLEY’S COMET has a period of 76 years and was last seen in 1986.

THE MILKY WAY GALAXY

The milky way is the name given to the faint band of light that stretches across the night sky. This light comes from stars and nebulae in our galaxy, known as the milky way galaxy or simply as ”the galaxy”. The galaxy is shaped like a spiral, with a dense central bulge that is encircle by four arms spiraling outwards and surrounded by a less dense halo. We cannot see the spiral shape because the solar system is in one of the spiral arms, the Orion arms(also called the local arm). From our position, the center of the galaxy is completely obscured by dust clouds; as a result, optical maps give only limited view of the galaxy. However, most complete picture can be obtained by studying radio, infra-red, and other radiations. The central bulge of the galaxy is a relatively small, dense sphere that contains mainly older red and yellow stars. The halo is a less dense region  in which the oldest stars are situated; some of  these stars may be as old as the galaxy itself (possibly 15 billion years). The spiral arms contain mainly hot, young, blue star, as well as nebula (clouds of dust and gas inside which stars are born). The galaxy is vast, about 100,000 light years across(a light year is about 9,460 billion kilometres ); in comparison, the solar system seems small, at about 12 light hours across(about 13 billion kilometres ). The entire galaxy is rotating in space, although the inner travels faster than those further out. The sun, which is about two-thirds out from the center, completes one lap of the galaxy about every 220 million years.

NEBULA AND STAR CLUSTERS

A nebula is the cloud of dust and gas inside a galaxy.  Nebula become visible if the gas glows, or if the cloud reflects starlight or obscure light from more distant objects. Emission nebulae shine because their gas emits light when it is stimulated by radiation from hot young stars. Reflection nebula shine because their dust reflects light from stars in or around the nebula. Dark nebulae appear as silhouettes because they block out light from shining nebulae or star behind them. Two types of nebula are associated with the dying stars: planetary nebula and supernova remnants. Both consist of expanding shell of gas that were once the outer layers of a star. A planetary nebula is a gas shell drifting away from a dying stellar core. A supernova remnant is a gas shell moving away from a stellar core at great speed following a violent explosion called a supernova. Stars are often found in groups known as clusters. Open clusters are loose groups of a thousand young stars that were born in the same cloud and are drifting apart. Globular clusters are densely packed, roughly spherical groups of  hundreds of thousands of older stars.

PLANETARY  NEBULAE

Planetary nebulae is a stage of star’s death. A planetary nebula, singular for nebulae is a shell of illuminated gas surrounding certain dying stars. Planetary nebulae have central stars and these stars were once lower to medium sized stars, like that of our sun, which eventually become a giant star and will soon become a white dwarf. As adult stars, the stars that make planetary nebulae burn hydrogen for fuel and leave helium ash as a byproduct. The hydrogen eventually runs out but these stars are massive enough to force the helium to be used as a secondary fuel thereafter. The helium is burned to a carbon  core as a byproduct. The helium eventually  begins to runs out as well. But unfortunately these stars are not massive enough to force the ignition of carbon as a tertiary fuel and they begin to die instead. As our stars becomes red giants and run out of helium fuel, they reignite the helium energy shells and increase the luminosity  called thermal pulse.ie, a thermal pulse is a temporary re-ignition of helium and increase of luminosity in a dying star. Luminosity is the total energy a star radiates out in one second. It is during the thermal pause, that the star’s outer gaseous layer were separate from its core, one that is now made up of carbon. In a sense, as the old star momentarily hits its gas pedal to use its remaining helium for energy production. During this time, it’s very hot inner core becomes exposed. The surface temperature is so high that the core will emit ultra violet radiations which is strong enough to ionize these shells of previously ejected gas. It is this that causes the gases to glow and produce all sort of amazing colors.

SUPERNOVA

A supernova is a massive explosion generated by a dying star. A star in our galaxy goes supernova approximately once every one hundred years. The explosion holds matter in the space that shines as brightly as an entire galaxy for short period. Stars are giant nuclear reactors producing energy by fusing hydrogen in to helium. Eventually however when  the star is out of hydrogen to fuse, the helium will fuse to heavier elements including iron. The star’s core shrinks and the outer layer expand, creating a red giant that consumes the surrounding planets. When the star runs out of helium, the star becomes a white dwarf and slowly fades away. When a large star depletes its helium, its core collapse within seconds, causing temperature of one hundred billion degrees. The outer layer of the star collapse as well. This massive explosion is known as supernova. Supernova generate enough energy to fuse elements heavier than iron. Gold, silver, uranium and other elements with higher atomic numbers are created in the supernovas. Then the star becomes a dense neutron star or a black hole. After the supernova, materials expelled  in the explosion forms a nebulae which has a massive inner stellar cloud of gas and dust. Over million years ,the gravity pulls nebulae materials together in to a dense hot core called a protostar. Protostars eventually become newborn stars.   

STELLAR SYSTEM

Our earth is a cosmic body. It is an insignificant speck of dust in the universe. The universe itself is a vast infinite expanse of space and matter. Mostly it is empty space or vacuum containing nothing seemingly physical. In this space matter is only sparely dispersed in a fashion and due to causes that are as yet beyond our complete understanding. The so-called concentration of matter in space have been differentiated by the scientists  into nebulae, galaxies, stars, planets, asteroids, comets and cosmic dusts and so on. Nebulae are enormous masses of  gaseous clouds without any structural differentiation. Galaxies are assemblies or associations of billions of stars in each case. All the stars in a galaxy are held together by the force of gravitation. There are millions of  galaxies each with billions of stars in our universe. A single galaxy with its constituent stars makes a stellar system.

THE STELLAR SYSTEM

A star system or a stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large number of stars bound by gravitational attraction is generally called a star cloud or galaxy, although, broadly speaking , they are also star systems. Stars systems are no to be confused with planetary systems, which include planets and similar bodies. A star system of two stars is known as a binary star system . If there are no tidal effects, no perturbation from other forces, and no transfer of mass from one star to the other, such a system is stable, and both stars will trace out an elliptical orbit around the center of mass of the system indefinitely. Example of  binary system are SIRIUS, PROCYON and CYGNUS X-1, the last of which probably consists of a star and a black hole.

A multiple star system consists of three or more stars that appears from earth to be close to one another in the sky. This may result from the stars actually being physically close and gravitationally bound to each other, in which case it is a physical multiple star and this closeness may be merely apparent in which case it is an optical multiple star(Meaning that the stars may appear to be close to each other when viewed from planet earth as they both seems to occupy the same point in the sky but in reality, one star may be much farther  from earth and the other, which is not readily apparent unless one can view them from a different angle.) Physical multiple stars are also commonly called multiple stars or multiple star systems. Most multiple star systems are triple stars. Systems with four or more components are less likely to occur. Multiple star systems are triple, trinary if they contain three stars; quadruple or quaternary if they contain four stars; quintuple or quintenary with five stars; sextuple or sextenary with six stars; septuple or septenary with seven stars. These systems are smaller than open star clusters, which have more complex dynamics and typically have from 100 stars to 1000 stars. Most multiple stars systems known are triple; for higher multiplicities, the number of known systems with given multiplicity decreases exponentially with multiplicity. For example in the 1999 revision of  TOKOVININ’S CATALOG OF PHYSICAL MULTIPLE STARS, 551 out of 728 system described are triples. However, because of selection effects knowledge of these statistics is very incomplete.

Multiple star systems can be divided in to two main dynamical classes; hierarchical system which are stable and consistent of nested orbits that don’t interact much and so each level of the hierarchy can be treated as a two-body problem, or the trapezia, which have the unstable strongly interacting orbits and are modeled as n-body problem, exhibiting the chaotic behavior.

ANATOMY OF THE UNIVERSE

The universe contains everything that exists, from the tiniest subatomic particles to galactic super clusters (the largest structures known). Nobody knows how big the universe is, but astronomers estimate that it contains about 100 billion galaxies, each comprising an average of 100 billion stars. The most widely accepted theory about the origin of universe is the Big Bang theory.

BIG BANG THEORY

The universe is everything. From the tiniest particle to the largest galaxies, to the very existence of space, time and life. But how did it all begin? The origin of the universe is the origin of everything. Multiple scientific theories and creation myths from around the world have tried to explain it’s mysterious origin. However the most widely accepted explanation is the  Big Bang theory.The Big Bang theory states that the universe began as a hot and infinitely dense point, only a few millimetres wide. It was similar to a supercharged black hole. About 13.7 billion years ago, this tiny singularity violently exploded. From this explosion(this Bang), all the matter, energy, space and time were created. What happened next is two major stage of the universe’s evolution called the RADIATION AND MATTER ERA that are defined by keys of hands that helps to shape the universe.

^{First came the RADIATION ERA. Number the domination of radiation after the Big Bang. This era is made of smaller stages called EPOCHS, that occurred within the universe’s first tens and thousands of years. first is the PLANCK EPOCH (temperature:10^40 kelvin, temperature after Big Bang: immediate )in which no matter existed. In the universe at this time, only energy and the four forces of nature called SUPER FORCE. At the end of the stage, however the gravity splits away from the super force. (time after Big Bang: 10^-43 seconds) named for the three remaining unified forces of nature. This epoch ended when one of the forces  called STRONG or STRONG NUCLEAR broke away. Then the INFLATIONRY EPOCH(temperature:10^33kelvin,time after Big Bang:10^-36seconds) began. During which the universe rapidly expanded. Almost instantly a from the size of an atom  to the size of a great fruit. The universe at this time was piping hot and it turned with electrons, quarks and other particles. Then came the ELECTROWEAK EPOCH(temperature:10^20kelvin,time after Big Bang: 10^ -32seconds), when the last two forces electromagnetic and weak finally split off. During the  next stage, the QUARK EPOCH(temperatureL10^20kelvin,time after Big Bang:10^-12seconds), all of the universe’s ingredients were present. However, the universe was still too hot and dense for subatomic particles to form.} 

^{Then in the HADRON EPOCH(temperature:10^10 kelvin, time after Big Bang:10^-6second), the universe cooled down enough for quark to bind together and formed protons and neutrons. In the LEPTON(temperature:10^12kelvin,time after Big Bang: about 1second) and NUCLEAR EPOCHS(temperature:10^6kelvin, time after Big Bang: about 100seconds) the radiation entered to the last two stages. The proton and neutrons underwent a significant change. They fused and created nuclei and doing so, they created the first chemical element in the universe, ’helium’. The universe’s new ability to form elements, the building blocks of matter acquired at the MATTER ERA. Much as the name suggests the matter era is defined by the  presence and predominance of the matter in the universe. It features three epochs that span billion of years, the vast majority of the universe’s lifespan and includes the present day. The first was the ATOMIC EPOCH(temperature:3000kelvin, time after Big Bang: 50,000years). In this stage, the universe’s temperature cooled down enough for electrons to attach to nuclei for the first time called recombination. This process helped to form the universe’s second element ’hydrogen’. This hydrogen along with the helium atoms dotted the universe with atomic clouds. Within the clouds, small pockets of gas may had enough gravity to cause atoms to collect.} 

^{These clusters of atoms formed during the GALACTIC EPOCH(time after Big Bang:200million years) became the seedlings of galaxies. Inside those galaxies, stars began to form and by doing so, there acquired the latest and current stage of the universe’s development, the STELLAR EPOCH(time after Big Bang: 3billion years).}

^{The formation of stars then caused a tremendous ripple effect and helped in shaping the universe as we know it. Heat within the stars caused the conversion of helium and hydrogen into almost all the remaining elements in the universe. In turn, those elements became the building blocks of planets, moons, lives, everything we see today. The ecosystem of everything was only possible because of them any stages of the universe’s development.}