The Earth and the Universe

Universe: Universe is vast space and anything that exist in this unlimited space.

Galaxy:

1. It is the cluster of billions of stars and everything in between them.
2. There are about 10¹² stars in a galaxy.
3. Diameter of galaxy is about 1000 light years to 1 million light years.
4. Name of our home galaxy is milky way galaxy.
5. The centre of galaxy is called galactic centre.
6. Time taken by the sun to revolve once around its galactic centre is 2.25X10⁸ years which is called cosmic year.
7. Solar system is about 30,000 light years far from galactic centre.
8. Name of nearest galaxy from milky way galaxy is Andromeda galaxy.

On the basis of shape there are 3 types of galaxy:

1. Irregular galaxy: Which does not have fixed shape. Some astronomer think that irregular shapes of these galaxies might caused by gigantic explosions at their centres.
2. Spiral galaxy: They have centre of bright stars and spiral arms around nucleus (centre).
3. Elliptical galaxy: They vary in shape from nearly spherical to flattened disc.

Solar Systems: The sun and other heavenly bodies like planets, satellites, meteor, comets, asteroids which revolve around the sun due to influence of its gravitational force is called solar system.

Planets: Planets are non-luminous celestial bodies with sufficient mass to have its own force of gravity,, nearly spherical in shape which moves around a star in its own fixed orbit.

Planets are also called wanderer of the sky since they change their position continuously with respect to stars.

Planets are classified into two groups:

Some informations about planet.

Mercury

1. It is smallest, nearest and fastest revolving planet.
2. It has satellite, no atmosphere.
3. Its surface temperature during day is 427°C and -170°C.
4. Rotation period is 59 day and revolution period 88 days.

Venus

1. It is brightest and hottest planet of solar system.
2. It is also called twin planet of Earth.
3. It is also called morning and evening star as it is seen only in morning and evening
4. It has no satellite. It has thick atmosphere of CO₂, Cloud of H₂O and H₂SO₄.
5. Temperature reaches up to 480°C at its surface.

Earth

1. It is only a planet where life exists.
2. Presence of suitable temperature atmosphere with sufficient oxygen and sufficient water. Due to presence of limonite at its surface it appears
3. Average surface temperature of 15°C.
4. It has only natural satellite called moon.

Mars

1. Due to presence of limonite at its surface it appears red so it is also called red planet.
2. It has two satellites called Phobos and Deimos.
3. Two polar ice caps are seen at polar region. Temperature during night reach up to -38°C.
4. It has atmosphere which consists of CO₂, H₂O, O₂ etc.
5. Dark patches are seen its surface which are called “seas of Mars”.

Jupiter

1. It is the largest planet of solar system.
2. It has 67 satellites.
3. Average surface temperature is -143°C
4. Rotation period 10 hrs and revolution period is 12 years.
5. Its atmosphere consist of mainly H₂ and He.
6. Its always surrounded by dense clouds of methane and Ammonia.
7. Red spot is seen in its atmosphere which is due formedde to atmospheric hurricane. hurricane.

Saturn

1. It is second largest planet of solar system.
2. Three rings of ice fragments and dust are present around the planet.
3. It has 62 satellites, Titan is largest satellite with diameter 5140 km.
4. Its atmosphere mainly consist of H₂ and He.
5. Its average surface temperature is -180°C.

Uranus

1. Its atmosphere consist of blue green clouds of methane, helium and Hydrogen.
2. It has 27 satellites.
3. Its average surface temperature i6 -216°C.
4. Its rotation period is 17 hours and revolution period is 84 years.

Neptune

1. It is farthest and coldest planet.
2. Its surface consists of H₂, He, Ne, silicate and water.
3. Its surface temperature is -220°C.
4. It consists of 14 satellites.
5. Triton is the biggest with diameter of 2706 km.
6. Its rotation period is 16 hours and revolution period is 164 years.

Sun

1. It is medium sized star.
2. Mass of sun is 770 times greater than mass of all other objects in solar system.
3. Main source of energy in sun is nuclear fusion reaction.
4. Sun blows wind of charged particles all around at very high speed (500 km/s) which is solar wind.
5. Mass of sun is 2X10³⁰ kg.
6. Volume s 1.4×10²⁷ m ³
7. Sun complete one revolution around galactic center in 2.25X10⁸ years, this year is called cosmic year.

Satellites

Satellites are the objects that revolve around the planet in their own orbit. There are two types of satellites they are:

1. Natural satellites
2. Artificial satellites

1. Natural Satellites: These are heavenly bodies that revolve around planet in their own fixed orbit. There are 173 natural satellites.

Moon

1. It is natural satellite of Earth.
2. It is 384400 km far from Earth.
3. Its diameter is 3476 m.

Sidereal month: Time taken by moon to complete one revolution around the Earth is called sidereal month. Its duration is 2733 days.

Synodic month: The duration between two nearest full moan is called synodic month. Its duration is 29.5 days.

2. Artificial satellite: The man made objects revolving around the Earth are called artificial satellites. Artificial Satellites are kept at a geostationary orbit at height of 36900 km from earth surface. Purpose of Launching artificial satellite ore:

1. To forecast weather.
2. For telecommunication.
3. To research and study.
4. For different military and spying operations.

Comet: Comets are the mass frozen gases, dust and ice that revolve around the sun highly elliptical orbit. These are non-luminous objects but when they approach closer to Sun, heat of sun evaporates ice present in them and as it reflects sunlight, it appears like star with tail. so they are also called tailed star.

A comet has 3 main parts they are: nucleus, coma and tail. The core of dust particles and ice is called nucleus. The Hazing cloud of gases around nucleus is called coma. Evaporated particles blown away by solar wind forms tail. The length of tail of a coma increases as it appears to sun it is because relatively it receives more heat from the sun which evaporates mate ice farming longer tail. Tail of a comet always appear in opposite direction of sun.

Meteors and Meteorites: When objects like piece of rock in space falls towards the Earth surface due to gravity of earth they burn completely in atmosphere producing bright streak of light, such objects are called meteors.

Very big and bright meteor is called fireball.

Some meteors which doesn’t burn completely and reach to Earth surface ore called meteorites. There are 3 types of meteorites. They are: stony, iron and stony iron.

Constellations: Constellations are the groups of few stars which are arranged in a fixed pattern and don’t change their relative position.

1. There are 88 constellations which were given name of animals, instruments etc.
2. All constellations are not visible at same time from same place.
3. 12 constellations are used as a sign of zodiac.

Some constellations are:

Ursa major (Saptarishi)

1. It has bright stars.
2. It is visible in the month of Baisakh and Jestha in Northern hemisphere.

Ursa major (laghu Saptarishi)

1. It has 7 stars.
2. Its shape is similar to Ursa major.
3. At the end of ursa minor there is polar star.
4. It is seen in month of Ashar and Shrawan.

Orion

1. It appears as hunter in the sky.
2. Three bright stars in straight line form belt of hunter.
3. It is commonly seen in Poush and Magh.
4. There are 7 bright stars in this constellation.

Zodiac signs:

1. Aries
2. Pisces
3. Aquarius
4. Capricorn
5. Sagittarius
6. Scorpio
7. Libra
8. Virgo
9. Leo
10. Cancer
11. Gemini
12. Taurus

Misconception of constellations:

1. People forecast about their future on the basis their signs of zodiac it does not have any scientific background.
2. It is believed that person born on new moon must marry person born on new moon. It doesn’t have any scientific support.
3. The babies born in mool Nakshatra are neglected socially in some communities. In fact, it doesn’t have scientific ground..
4. Zodiac signs connected with good or bad in marriage, tour, initiation of new work, type of job etc don’t have scientific background.

Importance of constellation:

Since ancient time constellations were used to find time and direction still they are used for the purpose.

Q. Differentiate between Star and planet

Q. Differentiate between Meteors and Meteorites

Q. Differentiate between Galaxy and constellation

Give reasons

a. Moon is not a planet.

A planet revolves around a star but moon revolves around a planet. So. moon is not a planet.

b. Earth is not a star.

Stars are luminous object having nuclear fusion reaction in them but Earth is non-luminous object and there is no possibility of nuclear fusion reaction so it not a star.

c. Comet is not a star.

Stars are luminous object with very high surface temperature but comets are non-luminous object with very low surface temperature, so it is not a star.

d. Venus is called as morning and evening star.

Venus appear as a bright object in the sky during morning and evening time. So, it is called morning and evening star.

e. Venus is the brightest and hottest planet even though it is farther than Mercury from the sun.

Atmosphere is absent in Mercury but there is thick atmosphere of Carbon dioxide in Venus which causes greenhouse effect increasing the surface temperature. Due to this, Venus is the brightest and hottest planet even though it is farther than Mercury from the sun.

Q. Identify following celestial bodies.

1. Temple tuttle: Comet
2. Titan: Satellite
3. Milky way: Galaxy
4. Triton: satellite