# Write a note on Venus.

ANS:


* Considering the distance from sun, it is the second planet of our solar system.
* It is a neighbour of earth and its composition is much similar to that of earth.
* It is the most brilliant planet.
* Its atmosphere consists of clouds of carbon dioxide.
* Unlike other planets, Venus spins in opposite direction from east to west. Due to this the sun appears to rise in the west on Venus.
* The core of Venus contains metals like iron and nickel whereas the crust is made of rocks containing iron, magnesium and silicate rocks.
* Its surface contains large mountains, valleys and volcanoes.
* It has no satellite (moon).

# Write a note on Earth.

ANS:


* Considering the distance from sun, earth is the third planet of our solar system.
* It is the only planet of our solar system where life exists because it has a thin layer of atmosphere which extends up to about 800 to 1000 km.
* Atmosphere protects us from meteors as they burn out due to friction before reaching the earth's surface.
* The ozone layer of atmosphere blocks ultraviolet rays of solar radiation from reaching the surface and protects us from its harmful effects.
* The natural Green House Effect due to gases like carbon dioxide and methane keeps the atmosphere warm enough to sustain life.
* Due to all these favourable circumstances life originated and sustained on the earth.
* The surface of the earth is solid (rocky) and has very large proportion of silicon dioxide.
* The core region is made up of molten (semiliquid) mass containing iron, magnesium, silicates, etc.
* It has one natural satellite (moon).

# Write a note on Uranus.

ANS:


* William Herschel discovered Uranus in 1781 AD.
* It is 64 times bigger than earth.
* Its diameter is 3.7 times that of the earth.
* Its core contains iron, magnesium and silicate rocks.
* It has layers of hydrogen and helium surrounded by icy clouds of methane and ammonia.
* It has 9 narrow rings of ash colour.
* It has 21 moons.
* It cannot be seen with naked eyes.

Write a note on Pluto.

ANS:[NOTE: (Only for information) Though we describe Pluto as a planet it has recently been removed from the list of planets due to certain reasons and at present it is no longer a planet. However, for us it is still a planet.]


* It is cold, dark and yellowish.
* Its density is similar to that of earth (therefore it is more like a terrestrial planet).
* Its core contains silicate rocks surrounded by water, methane and carbon dioxide in the solid state.
* Its outermost thin layer consists of nitrogen, methane and carbon dioxide.
* Its atmosphere mainly consists of methane.
* Its orbit is highly elliptical.
* Pluto forms a binary system with its moon Sheron (actually 'Charon') and they revolve around their common centre of gravity.
* It cannot be seen with naked eyes.

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# Write a note on Asteroids.

ANS:


* Asteroids are rocks with irregular shape(s) revolving around sun, which failed to assemble into planets (form planets) during the formation of the solar system.
* They are found in the belt between the orbits of Mars and Jupiter.
* There are about 1 lakh (0.1 million) asteroids.
* Orbits of about 4000 asteroids are known.
* Ceres is the largest asteroid known and it was the first asteroid to be discovered. Its diameter is about 1000 km.
* Vesta is another asteroid which is luminous and has diameter of about 400 km. It was discovered in 1807 AD.
* During their movement around sun, they sometimes collide with one another and get broken.
* The debris of asteroids sometimes enters earth's atmosphere in the form of meteors which burn out due to atmospheric friction.
* If a meteor is very large, it reaches the earth's surface. Then it is called a meteorite.
* Asteroids contain silicon, nickel, chromium and calcium with possibly gold and platinum.

# Write a note on 'shooting stars'.

ANS:


* If a substance from space enters earth's atmosphere, it is called a meteor.
* Such substances after entering earth's atmosphere burn due to friction and we see a streak of light in the sky.
* Due to this meteors are called 'shooting stars', though they are not stars.
* Maximum number of meteors are seen in the period between August and November.
* If a large-sized meteor fails to burn completely after entering earth's atmosphere, it strikes the surface of the earth. Such an object is called a meteorite.

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# Write a note on Comets.

ANS:





* In our solar system, there is a group of about a million celestial objects beyond Pluto which is called 'Cloud of Urt' [Wikipedia mentions it as : Cloud of Oort].
* These objects revolve around sun in a highly elliptical orbit and are called Comets.
* Comets are made up of dust and icy rocks.
* When a comet comes closer to sun, the ice gets vapourised forming a luminous tail.
* When the comet is nearest to sun, the tail is the longest and away from the sun.
* As the comet moves away from sun, the tail starts becoming smaller and ultimately disappears.
* Due to its tail a comet is called 'Tailed Star' despite the fact that it is neither a star nor is its tail permanent.
* The orbits of more than 750 comets are known.
* The most famous Halley's comet appears after a period of 76 years. It was last seen in 1986 AD and will be seen next in 2062 AD. It was named after Edmond Halley who had studied it in detail.
* In 1997 AD, a brilliant comet 'Helibob'[Wikipedia mentions it as : Hale Bopp] was seen for about 19 months even with naked eyes.
* A comet is basically made of water, carbon dioxide, ammonia, other frozen gases and dust particles.
* A detailed study has shown that the tail of a comet contains molecules of CO and HCN. These molecules are essential for the formation of certain complex compounds required for the origin of life.
* Some scientists believe that these molecules might have come to the earth from the tails of comets and resulted in the origin of life.
* Ancient people believed that the arrival of a comet was responsible for war, epidemic and natural calamities like flood. Modern science has, however proved that the arrival of a comet is a normal event and there is nothing to panic about.

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# Write a note on galaxy.

ANS:



* Stars are found in big clusters called galaxies.
* There are about 1011 galaxies in the universe and each galaxy contains about 1011 stars. Thus, there are in all about 1022 stars.
* Galaxies have generally two types of shapes: (i)Spiral (ii) Elliptical. Some galaxies have irregular shape.
* Most stars in elliptical galaxies are red indicating that they are very old. On the other hand the stars in spiral galaxies are bluish indicating that they are young. Thus, elliptical galaxies are older than the spiral galaxies.
* The number of spiral galaxies is greater than that of elliptical galaxies.
* The galaxy in which our solar system is situated is called the Milky Way. Milky Way appears as a milky belt stretching from North to South during dark night when the sky is clear.
* Milky Way is spiral in shape when viewed from the top. When viewed from the sides, it is seen bulging at the center and tapered towards the ends.
* The diameter of Milky Way is about 1 lakh (0.1 million) light years and the thickness of the middle (bulging) part is about 15000-20000 light years.
* Sun (and therefore the solar system)is located at about 30000 light years away from the galactic center.
* The sun completes one revolution around the galactic center in 22.5 crore (225 million) years at the speed of 250 km/s.

# Describe various orbits for artificial satellites.

ANS:


* Artificial satellites are kept in (i)Equatorial orbit (ii)Polar orbit.
* The orbit which is parallel to the equator is known as Equatorial orbit.
* If a satellite is placed at a height of 35786 km, its revolution period is 24 hours. Such asatellite is called 'Geostationary' as it appears stationary in space when observed from earth.
* By proper arrangement of several geostationary satellites we can link all corners of the earth with one another.
* Satellites in equatorial orbits do not require energy for revolutions.
* The orbit which is parallel to the Meridian is called Polar orbit.
* If a satellite is placed at a height of about 1000 km, its revolution period is about 2 hours. Such satellites complete several revolutions around earth in a day and they pass over a location on the earth at regular time interval.
* Remote sensing satellites of India visit any location on the earth at the interval of 21 days whereas America's Landsat takes 16 days for that.
* Like natural satellites, the orbits of artificial satellites are elliptical due to gravity effect.

# Mention uses of artificial satellites.
ANS:The uses of artificial satellites are as follows :


* In communication : For telecommunication (telephone), television transmission, radio networks and computer networks (internet).
* In Education Field : For teleconferencing and conducting country-wide classrooms.
* In Weather Forecasting : Getting prior information about monsoon, climatic changes, cyclones, etc.
* In Oceanography : To study changes occuring under sea and the aquatic life.
* In Geological Surveys providing information about water resources, mineral resources, changes in earth's crust, etc.
* In Agriculture to estimate the crop yield and to detect disease spread in crops.
* In defence to keep an eye on the activities of enemy country.