We all become familiar with the sky above right from our childhood days. We see the daily journey of the Sun across the sky, the waxing and waning of the Moon and the star-filled night sky. But in my childhood days we hardly ever gave a thought to what these celestial objects were or why they behaved or moved the way we saw them in the sky.
We gradually learnt about them as we grew up. Today, how-ever, things have changed. Children know a lot about the celestial objects thanks to the discoveries made by scientists over several centuries. The story of their discoveries has all the elements of a detective thriller. The exploration of space during the past four decades has further changed the scenario, revealing the solar system and the Earth's cosmic neighbourhood like never before.
To our distant ancestors, the Sun, Earth, Moon, planets and the stars made up the entire universe, with our Earth at the centre of it. Our ancestors believed that all the celestial bodies visible to the unaided eye-the Sun, Moon, five planets and the stars-move around the Earth in very complex paths. The ancient people did not even know what the stars and planets really were or how far they were from us.
There is, however, evidence that tells us that Vedic Indians, who probably lived more than 6,000 years ago, had considerable knowledge of astronomy. We find evidence of astronomical observations as early as 4,000 B.C. in the verses of the Rig Veda. But the oldest astronomical text in India is the Vedanga Jyotisha, which is dated about 1,400 в.с.
Gradually, with advances in science and technology, as telescopes and other observation tools were invented to study the universe, the real nature and shape of the universe gradually unfolded. With the help of astronomical records of hundreds of years, the Polish astronomer Nicolaus Copernicus in the 16th century established the Sun at the centre of the planetary family we call the 'solar system'. Later work by Johannes Kepler and Isaac Newton explained the way the planets moved around the Sun, thus solving a longstanding riddle of planetary motions. But more than that, these developments shifted the position of the Earth from being the hub of the universe to that of an insignificant member of the solar family.
The invention of the telescope in early 17th century brought in a revolution of sorts. For the first time, a single technological development radically changed all our ideas about the universe. It revealed the real nature of the celestial bodies like the Moon, the planets, and the Milky Way-the galaxy of which the Sun and its planetary family is a part. As more powerful telescopes came, distant galaxies were discovered which extended the limits of our universe manifold. The vastness of the universe gradually started unfolding. Astronomers discovered that the stars that we see as tiny specks of light in the night sky are actually suns, many of them hundreds or thousands of times larger than our Sun. In fact, it turned out that our Sun is a very ordinary and medium-sized star the like of which there are billions and billions in the universe, making up billions of galaxies like our Milky Way galaxy.
As techniques of astronomical observation were further refined and newer tools were put to use, giant clouds of gas and dust were discovered in space where stars were being born. Astronomers also recorded the dying moments of giant stars that end up with flashes of brilliance so bright that sometimes they can be seen in broad daylight. Stars were found to be mortal, like us humans. They were born from giant clouds of gas and dust, lived till old age and then died. Even our Sun will die eventually, but not in the near future. Astronomers say, it will continue to shine like it does now for at least 5,000 million years more.
Technological developments during the Second World War led to yet another breakthrough the discovery of radio waves coming from space that opened up a new dimension in our understanding of the universe. Galaxies and stars, and even our Sun, which appeared serene and shining steadily, turned out to be objects seething with extreme violence, spewing out highly energetic particles and powerful radiation. The universe as seen through the radio telescope appeared totally different from the visible universe we are familiar with.
Radio telescopes also brought forth new kinds of star-like objects, such as pulsars and quasars, the existence of which were never known before. Pulsars turned out to be fastspinning dead stars that behaved like extremely accurate celestial clocks, sending out preciselytimed pulses of radio waves. Quasars on the other hand are extremely distant objects, which emit extremely powerful radio waves. The real nature of quasars and the source of their enormous energy still remain a mystery.
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