Category Great Scientific Discoveries

          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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