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Note on Universe

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Universe

The aggregate of all existing things or the whole creation including all celestial bodies(heavenly bodies) and all of the space is called universe.The earth, the sun, the moon, etc whatever we see around us are in the universe.

Light year

It is defined as the distance traveled by the light in one year. Its value is about 9.5*10^15 m or 63066 AV. The sun takes 2.5*10^8 years to revolve around the galactic center. This time is called cosmic year.

Astronomical unit

It is defined as the distance between the sun and the earth and its value is about 1.5*1011. This unit is suitable for measuring the distance of the planets and satellites in the solar system 1AU=1.5*1011. the diameter of the solar system is about 78.1 AU.

Galaxies

A galaxy is a huge assembly of stars, dust and gasses, mutually held together by gravitational force. Millions of stars are present in the galaxy and the diameter of galaxy ranges from 1000 light years to one million light years. Our universe contains 10galaxies and each galaxy has about 1011 stars.

Types of galaxy

  1. Elliptical galaxy: The galaxy which looks like a flat elliptical disc are called elliptical galaxy.The stars of this type of galaxy are quite old and advance in evolution.It is the most common galaxy. 
  2. Spiral galaxy: A spiral galaxy consists of a center core part called nucleus above which system of arms and spiral out the number of arms which spiral about the nucleus may be one old and advance evolution. Adomic and milky way are spiral galaxy. 
  3. Irregular galaxy: The galaxy whose shapes are neither elliptical nor spiral but any irregular shape are called irregular galaxy.This type of galaxy are less brighter than the spiral galaxy. 

Constellation

Some of the stars in the galaxy stay in a group called constellation such group of stars staying in certain patterns can be seen clearly in clear moonless night. As looking from the earth, the group of stars resembles with some animals, a group of people, some object, etc. On the basis of what they resemble, they are given different names.About 88 constellations are known sufor and 12 of them are considered as zodiac. E.g. Ursa major, Scorpio, Orion, etc. 

Star

The star is self glowing heavenly bodies which generate the energy themselves by nuclear fusion reaction. The temperature of star is very high.About 3000 stars can be seen in the sky in clear night with naked eyes.The sun is the nearest star of earth. Alpha Centauri is the nearest star to the sun.

Sun

It is a medium sized star whose surface temperature is about 6000 degree Celsius. Sun revolve around the galactic center once in 2.5 x 108 years. Sun consist of 3 layers which are photosphere, chromosphere, and corona.

Importance of sun in solar system:

i) It is the center of solar system.

ii) All the planets revolve around the sun in their own orbit. iii) It provides light to all the planet to shine as they have no light of their own. iv) It provides heat and light energy for the lives of the planets if the life

iii) It provides light to all the planet to shine as they have no light of their own. iv) It provides heat and light energy for the lives of the planets if the life

iv) It provides heat and light energy for the lives of the planets if the life exists there.

 

Solar system: The giant family of sun including planets, asteroids, comets etc is called solar system.The diameter of the solar system is 10.5 light hour.

 

Planets: In solar system, eight planets are out of them first four planets which are present inside asteroid belt are called planets.They are Mercury, Venus, Earth and mars. But the remaining four planets are out of the asteroid belt are called inner planet. They are Jupiter, Neptune, Saturn and Uranus.

Some important facts about planet: 1) Nearest planet to sun = Mercury 2) Farthest planet to sun = Neptune 3) Fastest rotating planet = Mercury 4) Morning and evening star = Venus 5) Hottest planet = Venus 6) Green planet or living planet = Earth 7) Red planet = Mars 8) Largest planet = Jupiter 9) Planet having ring = Saturn 10) Planet that can float in water = Saturn

Satellites

a) Natural satellite:

They are those members of the solar system which revolve around the planets in their elliptical orbits. There are about 163 natural satellites. All the planets do not have satellites. Mercury and Venus have no satellite.Satellite are non-luminous bodies but they appear bright by reflecting the sunlight. The number of a satellite are different and are given below:

1) Mercury = 0 2) Venus = 0 3) Earth = 1 4) Mars = 2 (Phobos and Deimos) 5) Jupiter = 63 (Europa,Callisto) 6) Saturn = 60 (Titan) 7) Uranus = 27 (Miranda, Ariel) 8)Neptune = 13(Nereid)

b)Artificial satellite: An artificial satellite is made on the earth which moves continuously around the earth. The orbit of artificial satellite is elliptical and characterized by the parameters, apogee, perigee and inclination. Satellites are launched for different purposes.

Asteroid: The piece of rocks revolving around the sun between variable size and about 200 asteroids are present in a solar system. The diameter of asteroids varies from 100m to 700 km.The largest asteroid is Ceres which takes 4.6 years to revolve around the sun.

Comet: A comet is a frozen chunk of gas, dust and ice which when approaching the sun it begins to resemble a foggy star with a long shiny tail. They are block of icy rock materials and surrounded by a large mass of substance like water, ammonia, methane, etc. They make round the sun in highly elongated oval orbit, so they spend most of their time away from the sun.

Meteors and meteorites: Small pieces of rocks or metals which enter the earth atmosphere from outer space with very high speed are called Meteors. They are also called shooting star. If meteors is too big, then it will not burn completely and reach on earth. Some objects which land on the earth from the outer space are called a meteorite.

Evolution of stars

1) Formation of star: Scientist believed that stars are formed by the nebula. The nebula will make the collection of inter seller objects into various places into smaller parts. By any means, any one of the mass will develop the gravitational force and stars to attract the other patches towards itself. As a result of which its mass increases and the pressure on the circle also increases. And when the temperature of center reaches 5 x 106 degree Celsius then it is called a protostar. In protostar gradually, nuclear fusion reaction starts, due to excessive gravitational force, and it converts into stars.

2) Destruction of stars

  • Red giant: In stars gravitation is pulling all matter to its core and that force is balanced by the repulsive force created by a nuclear reaction in the core. When the stock of hydrogen starts to finish then gravitation starts to take over and compress the star. Due to high gravitational pressure helium starts to fuse to give carbon this release high amount of energy. Due to that energy stars expand their diameter. Red giants have radius from 100 million to a billion kilometers. Since the surface area of the star increases the produced energy is distributed over a large area. So the temperature of the star decreases. Our sun becomes a red giant in about 5.5 billion years from now. 
  • White dwarf: If the mass of red giant is smaller or equal to the sun then gradually the outer part will start to escape into space, then the inner core which is still hot starts to seem white, which is called white dwarf. 
  • Black dwarf: Gradually, the white dwarf continue to cool and finally it turns into black color which is called black dwarf. Finally, it starts to be invisible. 
  • Supernova: If the red giant is extremely big, then in core, further fusion reaction will continue. Then the helium core turns into carbon, oxygen, neon, silicon and finally iron and finally core of star explodes and such exploding star is called supernova.
  • Neutron star: Sometimes, after supernova explosion, nothing of star is left, the central core of the star which is equal to the size of earth. In which the proton and electron fuse together to give neutral neutron is called neutron star. 
  • PULSAR: A rapidly spinning neutron star surrounded by an extremely powerful magnetic field that can spin with it and is called pulsar. 
  • Black hole: A black hole is a remnant of a star so condensed that its gravitational pull is strong enough to prevent matter or even formed by identification contraction of heavy and large neutron stars under the action of their own gravity. 

 

  • The aggregate of all existing things or the whole creation including all celestial bodies and all of the space is called universe.
  • A galaxy is a huge assembly of stars, dust and gases, mutually held together by gravitational force . Galaxy are of three types elliptical, irregular and spiral.
  • Small pieces of rocks or metals which enter the earths atmosphere from outer space with very high speed are called Meteors.
  • Some objects which land on the earth from the outer space are called meteorite.
  • Star goes through the stages of red giant, white dwarf, black dwarf, supernova, neutron star, pulsars, and finally black hole.
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Very Short Questions

The four differences between a star and a meteor are:
Star Meteor
  1. A star is made up of hot gases like hydrogen.
  2. It has its own light.
  3. It is very large in size.
  4. It doesn't burn out.
  1. A meteor is made up of rock and metals.
  2. It doesn't have its own light.
  3. It is much smaller in size.
  4. It burns due to heat produce from friction against earth's atmosphere.

The two differences between comet and meteor are:
Comet Meteor
  1. It is made up of hard particles and embedded in ice.
  2. It has a head and a long tail that glows due to vaporizing ice crystals.
  1. It is made up of rock and metals.
  2. It does not have distinct head and tail but it glows due to heat produced from friction.

0%
  • 1AU (Astronomical Unit) equals to

    2.5*10^11
    1.5*10^11
    1.5*10^10
    1.9*10^11
  • The diameter of the solar system is about

    78.1 AU
    77.1 AU
    87.1 AU
    88.1 AU
  • The value of one light year is about

    8.5*10^15 m
    3.5*10^15 m
    9.5*20^15 m
    9.5*10^15 m
  • The surface temperature of sun is about

    8000 degree
    6000 degree
    1000 degree
    4000 degree
  • The diameter of the solar system is

    15.5 light hour
    11.5 light hour
    20.5 light hour
    10.5 light hour
  • The fastest rotating planet is

    Earth
    Mars
    Venus
    Mercury
  • Which planet is also known as morning and evening star?

    Earth
    Mars
    Venus
    Saturn
  • The planet that can float in water is

    Mars
    Earth
    Jupiter
    Saturn
  • The speed of light is

    298,792 km/sec
    299,792 km/sec
    299,872 km/sec
    199,792 km/sec
  • How many years does Ceres(largest asteroid) take to revolve around the sun?

    5.6 years
    6.4 years
    4.6 years
    3.7 years
  • Sun revolve around the galactic center

    once in 2.5 x 108 years
    twice in 3.5 x 108 years
    twice in 2.5 x 108 years
    once in 3.5 x 108 years
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jyotsna

what is black dwarf ?


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