GEOGRAPHY
The study of places and the interactions between people and their environs is known as geography. Geographers study the surface of the Earth and the various human societies that live there.
The ancient Greek scholar Eratosthenes is referred to be the "father of geography." He was the first to use the term "geography," and he also possessed a small-scale understanding of the planet, which enabled him to calculate the earth's diameter. Eratosthenes was a multi-talented individual.
As the Greek philosopher and explorer Herodotus showed in the fifth century B.C, knowledge was amassed about such novel and exotic locales. That knowledge came to be known as geography, a term first used in the third century B.C. as the title of Eratosthenes of Cyrene's book Geographica.
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UNIVERSE
The universe is commonly defined as the totality of everything that exists,including all physical matter and energy,the planets and star,galaxies and the contents of intergalactic space.
The study of universe is known as Cosmology.
The universe has no limit.
GALAXY
A galaxy is a vast system of billions of stars,which also contains a large number of gas clouds(mainly of hydrogen gas) and dust,isolated in space from similar systems.
There are about 100 billion galaxies ( 1011 galaxies) in universe,and each galaxy has,on an average 100 billion stars.(1011star)
The milky way galaxy is the home of the earth and our solar system.Its is spiral in shape.
Milky way Galaxy was formed 5 billion years after the Big bang.
Latest known galaxy is the Dwarf Galaxy.
According to the modern thought,universe can be classified into two parts namely
1) Atmosphere and 2) space.
Origin of the universe is explained by the BIG BANG THEORY,formulated and proposed by the Belgian astronomer and cosmologist Georges Lemaitre.
Andromeda is our near galaxy.
THE BIG BANG THEORY
All the matter in the universes was originally a concentrated lump called Primeral atom.
Big Bang was an explosion that occurred 15 billion year ago,leading to the formation of galaxies of stars and other heavenly bodies.
Since then,all galaxies have been flying away from one another causing expansion of the universe.
STAR
Clumps of dust and gas in a nebula come together due to gravity and form stars.
Stars are made of hot burning gases.
They emit light of their own and very large and very hot.
Light takes about 4.3 year to reach next nearest star proxima century.
THE SOLAR SYSTEM
The solar system consists of the sun,the eight planets and their satellities or moon,and thousands of other smaller heavenly bodies such as asteroids,comets and meteors.
The sun is the center of the solar system and all these bodies are revolving around it.
The gravitational pull of the sun keeps all the planets and other objects revolving round it.Thus,the motion of all the members of the solar system is governed mainly by the gravitational force of the sun.
Planets revolve around the sun in elliptical orbit.
In the solar system the planets nearest to the sun is mercury and the planets farthest from the sun is Neptune (not pluto).
The size of solar system has been estimated to at about 10 power 5 A.U.
The solar system is dominated by the sun which account for almost 99.9% of the matter in the whole solar system.
Pluto is a dwarf planet.
Mercury,venus,Earth,mars are called terrestrial planets and Jupiter,saturn,Uranus,neptune are called gaseous planets.
MEMBERS OF THE SOLAR SYSTEM
THE SUN
The sun is at the centre of the solar system.
Its size is thirteen lakh times as that of the earth.
Its is the nearest star to the Earth.
Its is an ultimate source of energy for life on Earth.
Its diameter is 14lakh kms.
Its is composed of 71%-Hydrogen,26.5%-Helium and 2.5% other elements.
Hydrogen and helium are mainly gases present in the sun.
Within the sun,hydrogen is converted to helium due to nuclear fusion releasing a tremendous amount of heat and light.
Its has a surface temperature of about 6000 degree celcius.
The temperature at the centre is around 15000000 degree celcius.
Shining surface of the sun is called photo sphere,it appears like a disc,radiates and acts as a source of energy.
The outer layer of suns atmosphere made up of thin hot gases is called CORONA.Corona is visible only during a total eclipse of the sun or with a special solar telescope called coronagraph.
The planet travels with the sun through millions of stars in our galaxy at speed of about 70,000 km/hr.
The Sun is about 150million kms away from the earth.
Planets
These are opaque bodies which continuously revolve around and are lighted by the sun.
There are eight planets in the Solar system.
A ninth planet has been recently discovered by NASA named as Carla.
The sequence of planets according to their distance from sun.is,mercury,venus,Earth,mars,Jupiter,saturn,uranus,neptune.
The sequence according to their size (in descending sequence from big to small) is
JUPITER>SATURN>URANUS>NEPTUNE>EARTH>VENUS>MARS>MERCURY
Jupiter is the biggest and mercury is the smallest planets of our system.
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