My Science School

          The greatest contribution made by Hans Christian Orsted is the discovery of electromagnetism. Some early scientists such as William Gilbert and Benjamin Franklin suspected a connection between electricity and magnetism. But, until the 1820s, electricity and magnetism were treated as separate entities.

          William Gilbert experimented with electricity in the early 17th century hoping to improve maritime navigation using magnetic compasses. Many of Benjamin Franklin’s experiments were aimed at a better understanding of the relationship between electricity and magnetism.

          Ultimately, it was Orsted who discovered the connection. He put a compass needle near a wire, then connected the wire to the terminals of a battery. The needle set itself at right angles to the wire, demonstrating that electricity could create magnetism.

          However, Orsted did not come up with a suitable explanation for the phenomenon immediately after the experiment. He engaged in intensive investigations for three months and then published his findings. Orsted proved that an electric current produces a magnetic field as it flows through a wire.

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          Asteroids are rocky worlds revolving around the sun which are too small to be called planets. They are also known as planetoids or minor planets.

          There are millions of asteroids of different sizes. When it comes to size, they may be a few feet wide or hundreds of miles long. Altogether, the combined mass of all asteroids is lesser than Earth’s moon.

          Giuseppe Piazzi, director of the observatory of Palermo in Sicily discovered Ceres, the first asteroid. It was mistaken as a new planet and Piazzi named it after the Roman goddess of agriculture, Ceres. Following this, more and more small bodies were discovered.

          Due to the limitations of the equipment of the time, they appeared only as points of light, like stars. This inspired the astronomer Sir William Herschel to propose the term asteroid, meaning star-like or star shaped.

         Hundreds of asteroids have been discovered till date and more are added every year. Millions more await discovery but may be too small to be seen from the earth.

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          Infrared radiation was discovered in 1800 by astronomer Sir William Herschel. When visible light passes through a prism, a rainbow of colours is seen. This is called a spectrum.

          Herschel discovered an invisible radiation in the spectrum that was lower in energy than the red light, through its effect on the thermometer. This was the first time that a form of light beyond visible light had been detected.

          Infrared radiation has a longer wavelength than visible light. It has applications in industrial, scientific, military, law enforcement, and medical fields. For instance, night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected.

          Ultraviolet (UV) radiation was discovered in the year 1801 by the German physicist Johann Ritter. He observed invisible rays just beyond the violet end of the visible spectrum which darkened silver chloride-soaked paper more quickly than violet light itself. Initially named oxidizing rays by Ritter, these later came to be known as ultraviolet light. The word ‘ultra’ means ‘beyond.’

          Through their discoveries Ritter and Herschel proved that there are invisible forms of light beyond both ends of the visible spectrum.

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          English astronomer Edmond Halley was the first person to predict the periodicity of Halley’s Comet. Subsequently, the comet was named after him.

          Comets were believed to make a single appearance. However, Halley showed that they could orbit the Sun and make periodic appearances. Though Halley was the first to prove the periodicity of comets, he was not the first to record their appearance. The return of Halley’s Comet to the inner solar system had been observed and recorded at least since 240 BC by astronomers. Chinese and European chroniclers had also made records of Halley’s Comet, although they did not realize that these were reappearances of the same object.

          Periodic reappearances of Halley’s Comet have been scientifically investigated even in the modern era. The three appearances from 1531 to 1682 were noted by Halley who recognized it as the same comet. In 1705, he predicted that it would return in 1758. Halley’s prediction came true and the comet was named in his honour. Unfortunately, Halley did not live long enough to see its return. He passed away in 1742.

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          Sir Isaac Newton discovered that white light can be broken down into its composite colours. Prior to this, most scientists believed that light was fundamentally white in Colour.

          When Newton started his experiments with light in the 1660s, our knowledge of light was saddled with many misconceptions. People thought that colour was a mixture of light and darkness, and that prisms coloured light. Even scientists like Robert Hooke were proponents of this theory. Realising the inconsistencies in the existing ideas about light, Newton set up a prism near his window, and projected a beautiful spectrum consisting of the rainbow of colours in visible light, 22 feet onto the far wall. To prove that the prism was not colouring the light, he recombined the light back together.

          Newton’s demonstration of the composition of light was a novel experience to the scientific world. Though he announced his discovery in 1670, the world took notice of it only in 1704 after he published his findings in his book Opticks. His discovery laid the foundation of modern physical optics.

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          The three laws of motion formulated by Isaac Newton laid the foundation of classical mechanics. Newton published these in his Philosophae Naturalis Principia Mathematics (Mathematical Principles of Natural Philosophy) in the year 1687. The laws of motion are still used to get people to the Moon.

           Newton’s first law takes hints from Galileo’s observations. Newton redefined Galileo’s observation that an object in motion will continue moving in the absence of a force. As Newton’s first law is a restatement of the law of inertia which Galileo had already described, Newton appropriately gave credit to Galileo.

           Newton’s first law states that the velocity (speed and direction) of an object only changes if a force acts on it. The second law states to what extent the object’s velocity will be changed by a given force. The third law states that when a body exerts some force on another one, the second will apply an equal force in the opposite direction, that is, every action has an equal and opposite reaction.

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          Gravity or gravitation is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light are brought towards one another. Isaac Newton was the first to discover gravity.

          It is said that Newton came up with the concept of gravity when he saw an apple fall, just as he was thinking about the forces of nature. Whether this particular incident happened or not, Newton realised that some force must be acting on falling objects like apples, or else, they would not start moving from the rest. He also realised that the moon would move away from the earth in a straight-line tangent to its orbit, if some force was not pulling it towards our planet. Newton called this force “gravity” and determined that gravitational forces exist between all objects.

          The new discovery cleared many of the long-standing doubts such as the reason why orbiting objects do not fly off into space.

          However, Newton’s theory could only describe how objects attracted each other and not why they did. The answer to this was suitably explained by Einstein’s Theory of Relativity.

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          As light is tremendously fast, measuring its speed was almost an impossible task. It was easier to calculate when light had travelled a long way.

          Ole Romer, a Danish astronomer accidentally found this in 1676. He noticed that the time between eclipses of Jupiter’s moons when they are hidden behind the planet varied throughout the year. Romer realised that it was because of variation in two things: the distance from Earth to Jupiter throughout the year and the distance travelled by light from the moons. His initial calculations estimated the speed of light to be about 220,000 km per second. Though this was 25 per cent slower than the correct speed, it was a significant start in the right direction. Christiaan Huygens later deduced that the speed of light is approximately 212,000 km/s.

          In 1809, astronomer Jean Baptiste Joseph Delambre estimated the time taken by light to travel from the Sun to Earth as 8 minutes and 12 seconds. This is quite close to the modern value, which is 8 minutes and 19 seconds, at a speed of 299,792.458 metres per second.

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          It is believed that light travels in straight lines. However, light bends very slightly at the edges of objects. Thus, the shadows formed will be a little smaller than if it were a simple straight line. This effect is called diffraction.

          The effects of diffraction of light were first carefully observed and characterised by Francesco Maria Grimaldi. Grimaldi also coined the word ‘diffraction’ from the Latin word diffringere, meaning, ‘to break into pieces’, referring to light breaking up in different directions. Grimaldi’s observations were posthumously published in 1665. A more conclusive study was done by Augustin-Jean Fresnel who made his calculations on diffraction public in 1815 and 1818.

          The discovery of diffraction supported the wave theory proposed by Christiaan Huygens. According to the wave theory, light is a stream of waves, with each wave made up of smaller wavelets. When light hits a glass at an angle, the wavelets that reached first would slow down. This causes light to bend. As the wave theory conflicted with Newton’s ideas, it was not accepted until the 19th century.

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          In the early 17th century, the concept of planetary motion was based on the ideas of Copernicus. People believed that planets orbited the Sun at a constant speed in perfect circles. This belief was challenged by the astronomer Johannes Kepler. He used the data meticulously gathered by his former employer Tyco Brahe, who had worked, without even the advantage of a telescope. Kepler calculated that rather than circles, the planets’ paths were ovals or ellipses and they did not have a constant speed. His discoveries certainly made people aware that the universe was not as simple as initially thought.

          Kepler’s first two laws on planetary motion were published in 1609 and the third one in 1619. The application of Kepler’s laws extends to the motions of natural and artificial satellites and unpowered space crafts in orbits in stellar systems or near planets. It is to be noted that these laws, as formulated by Kepler, do not take gravitational interactions between planets into consideration.

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          Jupiter has 79 known moons, almost making it a solar system by itself. In January 1610, Italian astronomer Galileo Galilei discovered four of Jupiter’s moons which are now called lo, Europa, Ganymede and Callisto. Originally, Galileo referred to them numerically as I, II, III, and IV. The first moon he discovered was lo and it is closest to Jupiter among the four. He published his observations in a book called The Starry Messenger. However, Simon Marius, who discovered the moons independently around the same time as Galileo, gave these moons their present names.

          Galileo’s discovery proved the importance of the telescope as a tool for astronomers. It made possible for humans to perceive celestial objects that remained unseen by the naked eye.

          Galileo’s discovery was a turning point in astronomical history as it put an end to the geo-centric model of the universe.

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          For almost 2000 years, Western thinking was influenced by the concept of universe being centred around Earth, advocated by Aristotle and Ptolemy. In the 16th century, the Polish astronomer Nicolaus Copernicus proposed a new concept.

          In his book On the Revolutions of the Heavenly Bodies, Copernicus proposed that it was the Sun at the centre of the solar system and not Earth. This model was called the heliocentric system in 1543.

          The Copernican model displaced Ptolemy’s geocentric model. Copernican heliocentrism became the launching point for modern astronomy. It described Earth as just another planet; placed third outward from the Sun.

          Copernicus also explained that stars are distant objects that do not revolve around the Sun. Instead, Earth rotates once in 24 hours. This causes the stars to appear as if they revolve around Earth in the opposite direction.

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          Earth’s circumference was first accurately measured more than 2,000 years ago by the Greek astronomer Eratosthenes.

         Eratosthenes heard that midday sunlight shines straight down to the bottom of deep wells, on the same day each year in the nearby town of Syene. This indicated that the Sun was directly overhead in Syene on that day. However, on the same day, sunlight fell only on the sides of the wells in Alexandria.

          Eratosthenes reasoned that the difference in the angle of incoming sunlight was due to the curved surface of Earth. By measuring this angle, he related the distance between Alexandria and Syene to the total dimension of the globe.

          On the day the Sun shone at the bottom of the wells in Syene, Eratosthenes measured the sun’s position in the sky over Alexandria.

          It was seven degrees away from the zenith, which meant that Syene was seven degrees away from Alexandria. He then made several calculations considering this angle and the distance between Alexandria and Syene, which is about 800 kilometres.

          There is only a difference of five per cent between the answer he got (42,000 km) back then and the value accepted today (40,075 km).

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          Why do some things float in water while the others sink? The answer to this question was found by the Greek scientist Archimedes. The principle he formulated is called the Archimedes principle.

          The Archimedes principle states that, when anything is immersed in a fluid even partly, it feels an upward push equal to the weight of the fluid it displaces. For instance, a ship launched into the ocean will sink until it displaces water equal to its own weight.

          There is an anecdote related to this discovery. King Hiero II of Syracuse wished to give a gold crown to a temple. The king him-self supplied the gold. However, he had a suspicion that the gold-smith mixed some silver to it. The king asked Archimedes to find the truth without damaging the crown. While taking a bath, Archimedes noticed that the level of the water in the tub rose as he got in. He realised that the submerged crown would displace an amount of water equal to its volume. Thus, the Archimedes principle was formulated.

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          People were aware of shocks from eels long before they knew about electricity. Egyptian texts dating back to 2750 BC referred to these fish as the “Thundered of the Nile”.

          Ancient cultures around the Mediterranean knew that certain objects such as rods of amber, when rubbed against cat’s fur could attract light objects like feathers.

          Electricity was nothing more than an intellectual curiosity until the 1600s, when the English scientist William Gilbert wrote De Magnete on his study of electricity and magnetism. However, Benjamin Franklin is often the one credited for the discovery of electricity. Franklin came up with the concept of electricity consisting of positive and negative elements. Franklin’s idea formed the basis of many future inventions.

          Franklin’s famous kite experiment was conducted to prove his assumption that lightning was a form of electricity. He flew a kite with a metal key attached to the string during a thunderstorm. As he expected, the key conducted electricity from the storm clouds, which was transferred to the kite and gave him a shock.

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