Tnpsc group 1, 2, 4 syllabus material Nature Of Universe Part – 3

Orbital Velocity

We saw that there are natural satellites moving around the planets. There will be gravitational force between the planet and satellites. Nowadays many artificial satellites are launched into the Earth’s orbit. The first artificial satellite Sputnik was launched in 1956. India launched its first satellite Aryabhatta on April 19, 1975.

Artificial satellites are made to revolve in an orbit at a height of few hundred kilometres. At this altitude, the friction due to air is negligible. The satellite is carried by a rocket to the desired height and released horizontally with a high velocity, so that it remains moving in a nearly circular orbit. The horizontal velocity that has to be imparted to a satellite at the determined height so that it makes a circular orbit around the planet is called orbital velocity.

The orbital velocity of the satellite depends on its altitude above Earth. Nearer the object to the Earth, the faster is the required orbital velocity. At an altitude of 200 kilometres, the required orbital velocity is little more than 27,400 kph. That orbital speed and distance permit the satellite to make one revolution in 24 hours.

Since Earth also rotates once in 24 hours, a satellite stays in a fixed position relative to a point on Earth’s surface. Because the satellite stays over the same spot all the time, this kind of orbit is called ‘geostationary’. Orbital velocity can be calculated using the following formula.

Microgravity is the condition in which people or objects appear to be weightless. The effects of microgravity can be seen when astronauts and objects float in space. Micro- means very small, so microgravity refers to the condition where gravity ‘seems’ to be very small.

All stars appear to us as moving from east to west, where as there is one star which appears to us stationary in its position. It has been named as Pole star. The pole star appears to us as fixed in space at the same place in the sky in the north direction because it lies on the axis of rotation of the Earth which itself is fixed and does not change its position in space. It may be noted that the pole star is not visible from the southern hemisphere.

Kepler’s Laws

In the early 1600s, Johannes Kepler proposed three laws of planetary motion. Kepler was able to summarize the carefully collected data of his mentor, Tycho Brahe  with three statements that described the motion of planets in a Sun-centered solar system. Kepler’s efforts to explain the underlying reasons for such motions are no longer accepted; nonetheless, the actual laws themselves are still considered an accurate description of the motion of any planet and any satellite. Kepler’s three laws of planetary motion can be described as below.

 First Law – The Law of Ellipses All planets revolve around the Sun in elliptical orbits with Sun at one of their foci. 

Second Law – The Law of Equal Areas The line connecting the planet and the Sun covers equal areas in equal intervals of time.

Third Law – The Law of Harmonies The square of time period of revolution of a planet around the Sun is directly proportional to the cube of the distance between sun and the planets

 International Space Station

ISS is a large spacecraft which can house astronauts. It goes around in low Earth orbit at approximately 400 km distance. It is also a science laboratory. Its very first part was placed in orbit in 1998 and its core construction was completed by 2011.

It is the largest man-made object in space which can also be seen from the Earth through the naked eye. The first human crew went to the ISS in 2000. Ever since that, it has never been unoccupied by humans. At any given instant, at least six humans will be present

in the ISS. According to the current plan, ISS will be operated until 2024, with a possible extension until 2028. After that, it could be deorbited, or recycled for future space stations.

Benefits of ISS

According to NASA, the following are some of the ways in which the ISS is already benefitting us or will benefit us in the future.

Supporting water-purification efforts

Using the technology developed for the ISS, areas having water scarcity can gain access to advanced water filtration and purification systems. The water recovery system (WRS) and the oxygen generation system (OGS) developed for the ISS have already saved a village in Iraq from being deserted due to lack of clean water.

Eye tracking technology

The Eye Tracking Device, built for a microgravity experiment, has proved ideal to be used in many laser surgeries. Also, eye tracking technology is helping disabled people with limited movement and speech. For example, a kid who has severe disability in body movements can use his eye-movements alone and do routine tasks and lead an independent life.

Robotic arms and surgeries

Robotic arms developed for research in the ISS are providing significant help to the surgeons in removing inoperable tumours (e.g., brain tumours) and taking biopsies with great accuracies. Its inventors say that the robot could take biopsies with remarkable precision and consistency.

Apart from the above-mentioned applications, there are many other ways in which the researches that take place in the ISS are helpful. They are: development of improved vaccines, breast cancer detection and treatment, ultrasound machines for remote regions etc

  ISS and International 

 Cooperation As great as the ISS’ scientific achievements are, no less in accomplishment is the international co-operation which resulted in the construction of the ISS. An international collaboration of five different space agencies of 16 countries provides, maintains and operates the ISS. They are: NASA (USA), Roskosmos (Russia), ESA (Europe), JAXA (Japan) and CSA (Cananda). Belgium, Brazil, Denmark, France, Germany, Italy, Holland, Norway, Spain, Sweden, Switzerland and the UK are also part of the consortium.

Points to Remember

The basic constituent of universe is galaxies which are really the collection of billions of stars.

 Scientists think that the universe began with the start of a massive explosion called the Big Bang. 

Depending on their appearance, galaxies are classified as spiral, elliptical, or irregular.

 Our Sun and all the planets in the solar system are in the Milky Way galaxy.

A group of stars forms an imaginary outline or meaningful pattern on the space, called constellations.

 The Sun and celestial bodies which revolve around it form the solar system.

Due to its right distance from the Sun, Earth has the right temperature, the presence of water and suitable atmosphere and a blanket of ozone.

Millions of pieces of rocks that were left over when the planets were formed and now revolve around the Sun are called asteroids.

 A body moving in an orbit around a planet is called satellite.

The ISS is intended to act as a scientific laboratory and observatory. Its main purpose is to provide an international lab for conducting experiments in space.


Asteroid               Small, rocky object orbiting the Sun.

Comet                  A chunk of dirty, dark ice, mixed with dust which revolves around the Sun.

Constellation                     A group of stars that can be seen as a pattern from Earth.

Galaxy                                  A group of stars, nebulae, star clusters, globular clusters and other matter.

Meteor                                A meteoroid that travels through the Earth’s atmosphere.

Meteorite                           A meteor that hits the Earth’s surface.

Milky Way                           A broad band of light that looks like a trail of spilled milk in the night sky.

Moon                                    Any natural object which orbits a planet.

Planet                                   A relatively large object that revolves around a star, but which is not itself a star.

Satellite                                Any object in outer space that orbits another object.

Space station                     A large, manned satellite in space used as a base for space exploration.

Star                                        A ball of constantly exploding gases, giving off light and heat.

Universe                              Everything in space, including the galaxies and stars, the Milky Way and the Solar System.


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 


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