The Universe



 



 



 



 



 



 



 



 



 



What are asteroids?



Asteroids are tiny heavenly bodies that move around the Sun. Most of them occur in the region between Mars and Jupiter. They are thought to be fragments left over from the formation of the solar system.





 



What is trajectory?



Trajectory is a general term for the path of any object moving in a force field such as a gravitational field that exerts a force on the object. Hence, the term trajectory can be applied to the path of space probe moving in a gravitational field.



 



 



 



 



What is an orbit?



When a small heavenly body moves around a larger one, the smaller body is said to orbit the larger one and the path followed by the smaller body is called its orbit around body. For example, the Earth orbits the Sun.



 



 



 



What are comets?



Comets are small heavenly bodies which orbit the Sun but regularly come close to the Sun. They are partially vaporized by the Sun’s heat and glow brightly for a short time when near the Sun. A comet consists of a central nucleus a few kilometers across and can be mixed with dust.



 


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The Universe


What is a natural satellite?



A natural satellite is a smaller natural heavenly body that moves around a planet. For example, the Earth has one natural satellite (the Moon), Mars has two and Venus has none. Natural satellites that orbit planets are also called the moons of their planets.



What is the difference between natural and artificial satellites?



Nowadays man-made objects can be launched into space from the Earth. Today, the satellites circling the Earth in space include the Moon as well as such man-made objects. Satellites such as the Moon are called natural satellites and man-made ones are called artificial satellites.



 


The Universe


What do we mean by the Solar System?



The solar system refers to the Sun and the various heavenly objects that move around the Sun.



Name the heavenly bodies that move around the Sun?



Planets, satellites, asteroids, comets etc.



What is a planet?



A planet is a major heavenly body. For example, the Earth is a planet and so are Venus and Mars.



What is a star?



A star is a massive heavenly body which emits enormous quantities of energy and appears to be glowing.



How many stars are there in a galaxy?



On an average, there are about a hundred billion stars in each galaxy.



How many stars are there in our galaxy, the Milky Way?



About four hundred billion stars.



Which star is nearest to the Earth?



The Sun.



How many stars are bigger in magnitude than the Sun?



In the Milky Way galaxy alone, there are five billion stars larger in magnitude than the Sun.



which heavenly body is nearest to the Earth?



The Moon.



 


The Universe

What is the universe?



The Universe consists of everything one can cognize through one’s senses and through observations using instruments.



The Sun and the Moon are components of the Universe one can easily observe but some objects too faint or too far away can easily only be observed through instruments like telescopes.



What are the main components of the Universe is general terms?



 The Universe consists of a vast emptiness called space with unknown boundaries, containing matter and energy in various forms.



In what forms does matter exist in the Universe?



Matter exists in the form of stars, plants, comets, satellites, meteors, asteroids, galaxies etc.



In what forms does energy exist in the Universe?



Energy exists in the form of heat, light, X-rays, microwaves, gamma rays, radio waves etc. What the eyes detect is only a minute range of wavelengths and frequencies (visible light) from a vastly broader spectrum of electromagnetic radiation. The heat and light from the Sun is a part of the energy can be detected only through instruments.



Does the Universe remain steady and unchanging?



No. The Universe is constantly changing with the passage of time.



 


What is the weight of our atmosphere?


            Our Earth is surrounded by a blanket of air from all sides. This enveloping blanket is called atmosphere. The atmosphere consists of a mixture of more than ten gases. In terms of volume, 78.05% of the atmosphere is nitrogen, 20.94% is oxygen and nearly 1% carbon dioxide. The remaining gases include argon, helium, neon, carbon monoxide, ammonia etc. The atmosphere also contains water vapour and dust particles, hydrocarbon, hydrogen oxide and sulphur compounds in variable amounts.



            Since all these gases are different forms of matter, they exert a downward force on the surface of the Earth and are regulated by the force of gravity. Man is rarely conscious of this weight since it presses on him from all directions, and his body is fully adjusted to it. The weight of the atmosphere can be determined by taking into account the masses of these gases and the force of gravity (weight = mass x gravity). We know that one mole of nitrogen weighs 28 gm. and that of oxygen 32 gm. Mole is the basic unit for measuring the amount of any substance in terms of atoms and molecules. 


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How can we locate the North Star?


          From the ancient times, the mariners in the Northern Hemisphere have been finding their way by observing the position of a bright star that is almost exactly in line with the North Pole. This star is called the North Star or the Pole Star or Polaris. Of course, with the invention of the compass, mariners no more depend on it. Moreover, the latest radio-direction-finding-technique has almost eliminated the need of the North Star. But since this star played a very important role in navigation for a long time it is desirable on our part to know the method of locating it.



          If you look towards the north of a clear night sky, you will see a group of seven stars that look like points placed along a dipper with a curved handle. When you have found such a group or constellation, look around in the same direction for another constellation. This too is shaped like a dipper, but with its handle curving in the opposite direction to that of the first dipper. The larger of these two is the Big Dipper, and the other one is the Little Dipper. They are also called Ursa Major (Big Bear) and Ursa Minor (Little Bear).



          Note that the forepart of the bowl of the Big Dipper is made up of two stars. The one at the top of the bowl is called ‘Dubhe’ and the other one is called ‘Merak’. These two stars are known as the pointers because if you draw a line from Merak to Dubhe, and continue the line for a distance equal to about four times the distance between the pointers, you will arrive at a bright star which is the one we are seeking - the North Star. 


How do astronauts walk in space?

          It appears strange but true that astronauts can walk in the space. This is so because in ordinary walking we rest our feet on the surface of the earth and the force of earth’s gravity pulls us towards it. But when there is nothing in the empty space – neither any surface to walk on nor any gravitational force to pull the feet down onto the ground – how does an astronaut walk in the space?



           Space walking by astronauts is quite different from the normal walking. To walk in the space the astronauts take the help of hand rockets which provide them the force to move. The hand rockets follow the principle of rocket propulsion. In rockets, the ejection of gas with a great force from the backside pushes the rocket forward with an equal thrust. This working principle is based on Newton’s third law of motion which states, ‘To every action there is always an equal and opposite reaction’. Similarly in hand rockets when the engine is powered the exhaust thrust pushes the rocket in the opposite direction and the astronaut walks along with this force as he carries the hand rocket with him. In fact, it is not ‘walking’ in the strict sense as there is no surface in the space to rest the feet but rather ‘floating’ – to express more accurately.



          But why do the astronauts walk in the space? Apart from experimental reasons, sometimes they are required to shift from one spacecraft to another or need to carry out a repairing work on the outer surface of the craft. During such operations they use the specially designed hand rockets and the direction of the exhaust outlet is pointed opposite to the desired direction of walking.



          The first spacewalk was made in March 1965 by a Soviet astronaut, A. Leonov, who stayed outside the aircraft for 24 minutes. Another important walk was made in 1973 when the American satellite Skylab was to be repaired for damage in the heat shield that made the craft dangerously hot. 


Who was the first man to land on the Moon?


For many centuries man had been dreaming of space travel and exploration of extra-terrestrial lands. The first concrete step in this direction was taken by the Russians when they launched the artificial satellite Sputnik I on 4 October, 1957. A month later on 3 November, 1957 a bigger Sputnik II was sent into the space. It took along, the first living creature, a dog named Liaka. Following closely on the heels of the Russians, the United States launched its first satellite Explorer I, on 31 January, 1958 triggering off a race between the two countries in space research. The first man in space was a Soviet cosmonaut, Yuri Gagarin, who orbited the earth on 12 April, 1961 in Vostok I.



In 1961, America started the famous Apollo project which was aimed at taking man to the Moon. It was an ambitious project with hurdles at every step. On 27 January, 1967 the Apollo project had a serious setback. During a practice session the astronauts Virgil Grissom, Edward White and Roger Chaffee were burnt to death in a fire aboard the spacecraft. This tragedy led to many modifications in the design of the spacecraft.



In July 1969, Neil Armstrong, Edwin Aldrin and Michael Collins went to the Moon in Apollo - 11. On 20 July, 1969 at 10.56 p.m. (GMT) Neil Armstrong put his first step on the surface of the Moon. He sent the message to the Earth, ‘That’s one small step for a man, one giant leap for mankind’. A little later, Aldrin also landed on the Moon. Michael Collins remained in the spacecraft. Armstrong and Aldrin stayed on the Moon for 21 hours and 35 minutes.



After this, four successful landings of the Apollo on the Moon followed. The final landing was on 11 December, 1972 by Apollo 17. Eugene Cernan and Harrison Schmitt spent 74 hours and 59 minutes on the moon and returned with 113.6 kg of lunar material. The first Indian to go to the space was Sq. Ldr. Rakesh Sharma in a joint Indo-Soviet flight on 3 April, 1984.



So far a total of 12 Americans walked on the Moon during the Apollo programme, bringing back 380 kg of rocks and soil. They have moved about 100 km of the lunar surface in a total time of 166 hours. 


Why does the sky appear blue?


          Our earth is surrounded by a blanket of air, which is called the atmosphere. It is mainly composed of nitrogen, oxygen, carbon dioxide, dust particles, water vapours and other gases. The light that comes to us from the sun has to travel through this atmosphere.



           Sun is the main source of light for earth. When the sunlight passes through the atmosphere, it is scattered by the dust particles, water and air molecules in all the directions. This is why, there is light all around after the sunrise.



          We know that the sunlight is composed of seven colours: violet, indigo, blue, green, yellow, orange and red. When the sunrays pass though the atmospheric molecules, the violet, indigo and blue colours get reflected most and the red colour least of them. Therefore, when we look at the sky the light that enters our eyes mainly consists of violet, indigo and blue colours. The mixture of these three colours is almost blue. That is why the sky appears blue.



          If the earth had no atmosphere, the sky would have just appeared dark. This fact becomes very clear when we look at the sky from the surface of the moon. It appears dark since there is no atmosphere in the moon. Similarly, the sky appears dark when we look from a spacecraft, because there are no light scattering particles in the higher space.



 


What are nebulae?

A nebula is a large cloud of gases and dust in outer space. There are two types of nebulae - diffuse nebulae and planetary nebulae. Diffuse nebulae are much larger than planetary nebulae. Some times a diffuse nebula is close enough to a star so that its dust reflects the light. A planetary nebula is an expanding cloud of glowing gas that surrounds a star.

If we look at the sky at night through a telescope, we can see many big black and white spots. These spots are called nebulae. The word ‘nebula’ comes from Latin which means ‘mist’ or cloud as they give the appearance of mist to us.



Black spots are called ‘black nebulae’, whereas white ones are called ‘bright nebulae’. In reality these nebulae consist of dust, gas and a cluster of stars. Many nebulae are situated in our Milky Way, but many more are outside it. Lot of information has been obtained about them with the help of powerful telescopes.



There are some 2000 nebulae in our Milky Way. It is estimated that there are millions of them existing outside it. Some of them are elliptical, some others are spiral shaped and some do not have any regular shape at all.



The temperature of the nebulae has been found to be varying from 6,000°C to 12,000°C. The temperature of the black nebulae is much less than that of the bright ones. Therefore, they appear black. They contain mostly hydrogen and helium gases. The nearest nebula is 300 light years away from us. And those situated outside the Milky Way are at least 150,000 light years away from us.



Scientists have photographed some of the nebulae. The photograph of the Crab nebula indicates that it is some 6000 light years away from earth. The photograph of one nebula resembles the head of a horse. It is, therefore, named the ‘Horse’ nebula. Another appears like a ring and thus it is called ‘Ring’ nebula. Nebulae are classified depending on whether they emit, reflect or absorb light. Scientists have already studied many nebulae. 


Why does thunder follow lightning?


          During the rainy season we often see lightning in the sky followed by thunder. Do you know what this lightning is and how thunder follows it?



          In ancient times whenever man saw lightning in the sky and heard thunder he used to believe that gods were angry and punishing him for some sin. Benjamin Franklin was the first person who, in 1872, scientifically explained the occurrence of lightning. In fact, whenever the sky gets overcast with clouds, the small particles of water present in them get charged due to air friction. In the process, some clouds become positively-charged, while some others negatively. When a positively-charged cloud approaches a negatively-charged one, there develops a potential difference of millions of volts between them. Because of this high voltage, there is a sudden electric discharge through the air between the two clouds and a streak of light is seen. This is called ‘lightning’. The electric discharge through the air produces a large amount of heat due to which the atmospheric air suddenly expands. With this sudden expansion, the innumerable molecules of the air collide with one another and produce sound. This is called ‘thunder’. In other words, the thunder is the acoustic shock waves, which may be a sudden clap depending upon the lightning path. Although lightning and thunder are produced simultaneously, yet we see the flash of lightning first. It is so because the speed of light is very high i.e., 300,000 kms per second. On the other hand speed of sound is only 332 metres per second. Thus, because of high velocity, light immediately reaches our eyes, but the sound takes some time to reach our ears.



          Whenever a charged cloud passes by some tall tree or high building, by induction, it produces the opposite charge on that tree or building. When the amount of charge so produced is very high, a giant electric spark travels between the cloud and the ground. It is then said that lightning has struck such a tree or building.



          To protect high buildings from such mishaps, pointed rods of copper or some other metal are fixed on the top of buildings which run to the bottom and are buried deep in the earth. These are called ‘lightning conductors’. Whenever some charged cloud passes by such a building and produces opposite charge on it, the charge goes to earth through the metal rod and does not damage the building. This how buildings are protected from the lightning.



 


Why can’t we see stars during the day?


          The stars become visible in the sky as soon as there is darkness after the sunset. As the darkness increases, the number as well as brightness of the stars also increase. The number of visible stars dwindles with the approach of dawn. Only very bright stars remain visible. At sunrise all the stars disappear. Do you know why stars are not visible during the day?



          Some people think that as the sun disappears during the night, the stars too vanish during the day. But this is not correct. The stars never disappear. They simply become invisible during the day because of the brightness of the sun’s rays. In fact, the dust, gas and water vapours present in the atmosphere scatter the sun’s rays in all the directions. Due to this, the whole atmosphere starts shining. The light of stars is very weak as compared to the sunlight and as such it fails to make any impact on our eyes. We, therefore, can not see the stars during the day. This fact becomes clear by just observing a burning lamp. During night a lamp’s flame is visible from a long distance, but during the day the same is not visible to us even from a short distance. This implies that even a feeble light can reach our eyes during the night and as such stars become visible to us at night. Had there been no atmosphere, the stars would have been visible even during the day. Stars are visible in the space even during the day because in space you are beyond the atmosphere. 


What are asteroids?


                We all know that in our solar system there are nine planets which always revolve round the sun in elliptical orbits. In addition to these planets, there are many small bodies or irregular lumps of rocks which orbit the sun. These small heavenly bodies are called ‘asteroids’ or ‘planetoids’.



               There are about 100,000 asteroids but majority of them are two small to be seen from the earth. Each asteroid has its own orbit in which it revolves round the sun. The biggest asteroid is ‘Ceres’. It measures 1/800th of the size of the earth. The Italian astronomer Piazzi discovered this asteroid in January 1801. The ‘Vestal’ is the only asteroid visible to the naked eye though it was discovered after “Ceres”. The diameter of these asteroids range from 1 km to 800 kms. The total mass of these asteroids is 1/3000th of that of the earth. Two-thirds of the asteroids revolve in orbits lying between the orbits of Mars and Jupiter. Some asteroids revolve between Mercury and Mars also. The asteroid ‘Incarus’ is one of them. The orbit of the asteroid named ‘Hidalgo’ lies between Mars and Saturn. The asteroids ‘Hermes’ and ‘Eros’ are within a range of a few million kms from the earth.



               Eros is a small asteroid that wanders from the asteroid belt and comes within a range of 25.6 million kms from the earth in every seven years, i.e. closer than any other body in the solar system except the moon. It was discovered by G.Witt, in 1898. A second asteroid belt beyond the orbit of “Pluto” has been assumed by the scientists in their recent studies.



               These bodies appear like saucers under powerful telescopes. Some of them are very bright, while some others are faint. Their sizes have been determined on the basis of their brightness.



               Most of the asteroids are constituted of the same ingredients of which the rocks on the earth are made. Their surface temperatures however differ. Scientists believe that asteroids might have originated when some big planets exploded in space and its small pieces then started revolving round the sun. However, nothing can be said about their origin correctly. 


Why are all the heavenly bodies round?


           The earth is round, and so are the sun and the moon. Even the planets, their satellites and the stars are also spherical. Do you know why all these heavenly bodies are spherical in shape?



           According to a law of science, every physical system in the universe tries to attain a state of minimum energy for maximum stability. It is an established fact that if a sphere is made from a given volume of any material it will have the least surface area compared to any other form. Consequently the spherical bodies have the minimum surface energy. Substances try to acquire a round form like a football in order to achieve the state of minimum energy, that is, the state of maximum stability. This is why the sun, the moon, the stars, the earth and all other heavenly bodies have a spherical shape.



           The rain drops are also spherical. It is so because the surface of the spherical drops has the minimum energy and maximum stability. Whatever be the process of producing the water drops, they immediately try to acquire a spherical shape.





           Atoms and molecules are also spherical in shape. Even the electrons, protons and neutrons present in the atoms are also spherical.



          You might have observed that every man tries to earn the most with the least effort. Every student tries to secure maximum marks after putting in the minimum labour. Thus we see that the tendency to come to the minimum energy state is found in all the living and non-living bodies. As soon as a substance acquires the minimum energy state, its shape becomes spherical.



 



 


Why Apollo 17 is considered the last moon mission?

 



The Apollo 11 was the first manned mission that successfully landed on the Moon. Manned by three American astronauts, Apollo’s lunar module, the Eagle, landed on the face of the Moon on July 20th, 1969. Neil Armstrong and Edwin Aldrin were the first men to walk on the Moon. Three years later, Apollo 17 was the last Apollo Mission to land men on the Moon. It carried the only trained geologist to walk on the lunar surface – Harrison Schmitt. The Apollo 17 astronauts traversed the greatest distance on the Moon, using the lunar roving vehicle. They also returned the greatest amount of samples of rock and soil. The last human being to walk on the Moon was the Commander of Apollo 17, Eugene Cernan. No humans have visited the Moon since December 14th 1972.