World celebrates 400 years of astronomical discoveries

The year 2009 was declared the International Year of Astronomy by the United Nations, in its 62nd General Assembly.

This year marks the 400th anniversary of two important developments in astronomy. In the year 1609 Galileo Gallilei discovered the telescope as a tool for observing the heavens, while  Johannes Kepler wrote his book Astronomia Nova, in which
he laid down his laws of planetary motion. Both these  developments marked a giant leap forward in our perception of the heavens.

Take Galileo’s achievement first. The telescope had just been discovered and its value in bringing distant objects closer was beginning to be appreciated. For example an army general could spot the enemy’s actions from afar; or a hiker on the mountain could get his bearings right by observing the distant landscape.

Galileo had the remarkable idea: why not turn this remarkable instrument towards the sky and bring the distant heavenly bodies closer? With his experimental genius he made a few necessary modifications in the design and produced a working instrument. Its effect was indeed remarkable.

He could see that the apparently smooth surface of the Moon was full of craters and hills. And the planet Jupiter had four moons of its own, all circulating around the planet just as our Moon goes around the Earth. And when he trained his telescope on the shining Sun, he made an even more remarkable discovery, that the solar surface had a few black spots on it. This was the first time anyone on Earth had seen the sunspots, or for that matter the lunar craters and Jupiter’s satellites.

Kepler’s book published in the same year marked the culmination of his investigations for ten years, on the nature of planetary motion. For two millennia it was believed that the Earth is fixed in space and the Sun, the Moon and the planets all go round it.

A few decades earlier, at the risk of inviting the wrath of the Establishment, Copernicus had asserted that the system of planets including the Earth, all move around the Sun which was the fixed body of the solar system. Kepler took the Copernican ideas a great deal further and discovered the detailed rules governing the motion of planets.

Both Kepler and Galileo faced considerable opposition from the Society. Kepler’s ideas, following Copernicus, seemed to wrest the importance from the Earth and vest it in the Sun. Apart from factual aspects, this assertion challenged the widely assumed special status of the Earth in the cosmos and by implication man’s position in the universe.

Galileo’s findings with his new toy, the telescope, showed that the creation is not as perfect as one would have liked: the Moon has a rugged surface, the Sun has dark spots and we have to accept the motion of moons around a body other than the Earth. All these findings were against the prevalent ideas with belief in God creating a perfect world in which everything revolved around a fixed Earth.

Thus 1609 marked a watershed in our understanding of the cosmos and during the IYA we will come to appreciate how great those contributions of Galileo and Kepler were.

Astrophysician Jayant Narlikar and Thanu  Padmanabhan, theoretical physicist, will contribute to DNA’s special series through 2009, designated the International Year of Astronomy. This is the first article in the series