about universe

universe

                                                                                          Introduction

                In the earlier days, before the invention of astronomical instruments,people thought that Earth is the centre of all the objects in the space.  This was known as the geocentric model, held by Greek astronomer Ptolemy (2nd century), Indian astronomer Aryabhatta (5th century) and manh astronomers around the world.  Later polish atronomer Nicolaus Copernicus proposed the heliocentric model (helios = Sun), with Sun at the centre of the solar system.  Invention of the telescope in the Netherlands, in 1608, created a revolution in astronomy. 

Building block of the Universe

               The basic constituent of the universe is luminous matter i.e, galaxies which are really the collection of billions of stars.  The universe contains everything that exists including the Earth, planets, stars, space, and galaxies.  This include all matter, energy and even time.  No one knows how big the universee is.  It could be ifinitely large.  Scientists, however, measure the size of the universe by what they can see.  This is called the 'observable universe'.  The observable universe is around 93 billion light years (1 Light year = the distance that light travels in one year, which is 9.4607 x 10  kms) across.

Stars

             Stars are the fundamental building blocks of galaxies.  Stars were formed when the galaxies were formed during the Big Bang.  Stars produce heat, light, ultraviolet rays, x-rays, and other forms of radiation.  they are largely composed of gas and plasma (a superheated state of matter).  Stars are built by hydrogen gases.  Hydrogen atoms fusetogether to form helium atoms and in the process they produce large amount of heat.  In a dark night we can see nearly 3,000 stars with the naked eye.  We don't known how many stars exist.  Our universe contains more than 100 billion galaxies, and each of theose galaxies may have more than 100 billion stars.

             A group of stars forms an imaginary outline or meaningful pattern on the space.  they represent an animal, mythological perrson or creature, a god, or an object.  This group of stars is called is called constellations.  People in different cultures and countries adopted their own sets of constellation outlines.  there are 88 formally accepted constellations.  Aries, Gemini, Leo, Orion, Scorpius and cassiopeia are some of the constellations.

The Solar System

              Sun and the celestial bodies which revolve around it form the solar system.  It consists of
large number of bodies such as planets, comets, asteroids and meteors.  The gravitational force of attraction between the Sun and these objects keep them revolving around it.

The sun

    

              The Sun is a medium sized star, a very fiery spinning ball of hot gases.  Three quarters of the sun has hydrogen gas and one quarter has helium gas.  It is over  million times as big as the Earth.

Hydrogen atoms combine or fuse together to form helium under enormous pressure.  This process, called nuclear fusion releases enormous amount of energy as light and heat .  It is this energy which makes Sun shine and provide heat.  Sun is situated at the centre of the solar system.  The sttong gravitational fields cause other solar matter, mainly planets, asteroids, comets, meteoroids and other defbris, to orbit around it.  Sun is believed to be more than 4.6 billion years old.

planets

             A planet revolves around the Sun along a definite curved path which is called an orbit.  It is ellliptical.  The time taken by a planet to complete one revolution is called its period of revoulution .

             Besides revolving around the Sun, a planet also rotates on its own axis like a top.  the time taken by a planet to complete one rotation is called its period of rotation.  The period of rotation of the Earth is 23 hours and 56 minutes and so the length of a day on Earth is taken as 24 hours.

mercury 

             Mercury is a rocky planet nearest to the Sun.  It is very hot during day but very cold at night.  Mercury can be easily observed thorough telescope than naked eye since it is very faint and small.  It always appears in the eastern horizon or western horizon of the sky.

Venus

              Venus is a special planet from the Sun, almost the same size as the Earth.  It is the hottest planet in our solar system.  After our moon, it is the brightest heavenly body in our night sky.  This planet spins in the opposite direction to all other planets.  So, unlike Earth, the Sun rises in the west and sets in the east here.  Venus can be seen clearly through naked eye.  It always appears in the horizon of eastern or western sky.

Earth

The Earth

              The Earth where we live is the only planet in the solar system which supports life.  Due to its right distance from the sun it has the right temperature, the presence of water and suitable atmosphere and suitable atmosphere and a blanket of ozone.  All these have made continuation of life possible on the Earth.  From space, the Earth appears bluish green due to the reflection of light from water and land mass on its surface.

Mars

             The first planet outside the orbit of the Earth is Mars.  It appears slightly reddish and therefore it is also called the red planet.  It has two small natural satellites (Deimos and Phobos).

jupiter

             Jupiter is called as Giant planet.  It is the largest of all planets (about 11 times larger and 318 times heavier than earth ).  It has 3 rings and 65 moons.  Its moon Ganymede is the largest moon of our solar system .

Saturn

            Known for its bright shiny rings, Saturn appears yellowish in colour.  It is the second biggest and a giant gas planet in the outer solar system.  At least 60 moons are present - the largest being Titan . Titan is the only moon in the solar system with clouds.  Having least density of all (30 times less than earth ), this planet is so light.

Uranus

            Uranus is a cold gas giant and it can be seen only with the help of large telescope.  It has a greatly tilted axis of rotation.  As a result ,in its orbital motion it appears to roll on its side.  Due to its peculiar tilt, it has the longest summers and winters each lasting 42 years.

Neptune

             It appears as Greenish star. Iat is the eighth planet from the Sun and is the windiest planet.  Every 248years, pluto crosses its orbit.  This situation continues for 20 years.  It has 13 moons -triton being the largest.  Triton is the only moon in the solar system that moves in the opposite direction to the direction in which its planet spins.