Tnpsc group 1, 2, 4 syllabus material nature of universal part-9


An object that revolves around a planet in a stable and consistent orbit is called a satellite. Satellites can be classified into two categories – natural and artificial.

Natural satellites

All natural objects revolving around a planet are natural satellites. They are also called moons. Most moons are spherical, the ones that are not usually asteroids or meteors that were captured by the strong gravity of a planet. All planets except mercury and Venus in our solar system have moons. Earth has only one moon- whereas planets like Jupiter and Saturn have more than 60 moons.

galileo galilei

Artificial satellites

Artificial satellites are man-made objects placed in an obit to rotate around a planet – usually the Earth. The world’s first artificial satellite launched was Sputnik-1 by Russia, Aryabhatta was the first satellite launched by India. These satellites are used in television and radio transmission, studying agriculture yield, locating mineral resources, weather forecasting, locate different places on earth.


The Indian Space Research Organisation (ISRO) is the space agency of the Government of India headquartered in the city of Bangalore. Its vision is to “harness space technology for national development while pursuing space science research and planetary exploration.”

Formed in 1969, ISRO superseded the erstwhile Indian National Committee for Space Research (INCOSPAR) established in 1962 by the Scientist Vikram Sarabhai. The establishment of ISRO thus institutionalized space activities in India. It is managed by the Department of Space, which reports to the Prime Minister of India. ISRO built India’s first satellite, Aryabhatta, which was launched by the Soviet Union on 19 April 1975.

It was named after the Indian astronomer Aryabhata. In 1980, Rohini became the first satellite to be placed in orbit by an Indian-made launch vehicle, SLV-3. ISRO subsequently developed two other rockets: the Polar Satellite Launch Vehicle (PSLV) for launching satellites into polar orbits and the Geosynchronous Satellite Launch Vehicle (GSLV) for placing satellites into geostationary orbits.

These rockets have launched numerous communication satellites and earth observation satellites. Satellite navigation systems like GAGAN and IRNSS have been deployed. In January 2014, ISRO used an indigenous cryogenic engine in a GSLV-D5 launch of the GSAT-14.


ISRO sent a lunar orbiter, Chandrayan -1, on 22 October 2008 and a Mars orbiter, Mars Orbiter Mission, on 5 November 2013, which entered Mars orbit on 24 September 2014, making India the first nation to succeed on its first attempt to Mars, and ISRO the fourth space agency in the world as well as the first space agency in Asia to reach Mars orbit. On 18 June 2016 ISRO set a record with a launch of 20 satellites in a single payload.

On 15 February 2017, ISRO launched 104 satellites in a single rocket (PSLV-C37) and created a world record. ISRO launched its heaviest rocket, Geosynchronous Satellite Launch Vehicle Mark III (GSLV-Mk III), on 5 June 2017 and placed a communications satellite GSAT-19 in orbit. With this launch, ISRO became capable of launching 4 ton heavy satellites. ISRO launched Chandran 2 on July 22, 2019, Geosynchronous Satellite Launch Vehicle (GSLV-Mk III). It entered the Moon’s orbit on August 20, 2019 and its lander landed on the Moon on September 7.

Points to Remember

The field of study of the universe is called astronomy.

The universe consists of galaxies, planets, stars, meteorites, satellites and all other forms of matter and energy.

The half moon during the waxing period is called as first quarter and the half moon during the waning period is called as third quarter.

The word crescent refers to the phases where the moon is less than half illuminated. The word gibbous refers to phases where the moon is more than half illuminated.

The reversal of direction of planets is called as ‘retrograde motion’.

The geocentric theory followed by the ancient people proposed that the Earth is at the centre and the sun and other planets revolve around it.

The helio-centric theory states that the sun I at the centre and the planets revolve around it

Galilio gave the observational evidence to support the heliocentric theory

There are at least hundreds of billions of galaxies in the Universe.

A galaxy is a large collection of stars or cluster of stars and celestial bodies held together by gravitational attraction.

A constellation is a recognizable pattern of stars in the night sky when viewed from the Earth.

An object that revolves around a planet in a stable and consistent orbit is called a satellite.

The Indian Space Research Organization (ISRO) is the space agency of the Government of India headquartered in the city of Bangalore.


10 std tamil study material

அன்னை மொழியே 

இரட்டுற மொழிதல் 

காற்றே வா




பெருமாள் திருமொழி 


நீதி வெண்பா 



முத்துக்குமாரசாமி பிள்ளைத்தமிழ் கம்பராமாயணம் 

ஏர் புதிதா ? 







9 std tamil study material


தமிழ்விடு தூது 





ஓ , என் சமகாலத் தோழர்களே


குடும்ப விளக்கு 


இராவண காவியம்

நாச்சியார் திருமொழி 

சீவக சிந்தாமணி 



ஒளியின் அழைப்பு 

தாவோ தே ஜிங் 

யசோதர காவியம் 



8 std tamil study material

தமிழ்மொழி வாழ்த்து 

தமிழ்மொழி மரபு 


கோணக்காத்தும் பாட்டு 

நோயும் மருந்தும் 

வருமுன் காப்போம் 

கல்வி அழகே அழகு 

புத்தியைத் தீட்டு 


பாடறிந்து ஒழுகுதல் 

வளம் பெருகுக 


படை வேழம் 

விடுதலைத் திருநாள் 

ஒன்றே குலம் 

மெய்ஞ்ஞான ஒளி 


இளைய தோழனுக்கு

7 std tamil study material

எங்கள் தமிழ் 

ஒன்றல்ல இரண்டல்ல 


புலிதங்கிய குகை 

கலங்கரை விளக்கம் 

இன்பத்தமிழ்க் கல்லி 

ஒரு வேண்டுகோள் 


வயலும் வாழ்வும் 

புதுமை விளக்கு 

அறம் என்னும் கதிர் 


6 std tamil study material


அறிவியல் ஆள்வோம் 


துன்பம் வெல்லும் கல்வி 

ஆசாரக் கோவை 

கண்மணியே கண்ணுறங்கு 

நானிலம் படைத்தவன் 

கடலோடு விளையாடு 


Ration and proportional



Number series

L.C.M and H.C.F

Simple Interest

Compound Interest


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