Nearly four hundred years ago, an instrument called a spyglass was causing rumours across Europe for its wondrous abilities. Galileo Galilei was visiting his friend Paolo Sarpi in Venice when he heard about the miraculous power of the spyglass, a long tube fitted with glass lenses that enabled one to see distant objects as if they were much closer. Back in Padua, where he served as a professor of Mathematics, he spent about a month perfecting the design of the instrument and then presented his own version which was much better than prevailing instruments. His major achievement was to derive a mathematical relation for the magnifying power in terms of the focal lengths of the two lenses, the eye–piece and the objective. Other people played with such tubes during that period but they could not improve the power beyond two to three times, merely by using a hit and trial method. Initially, Galileo saw that the instrument could be useful to track distant enemies on land or at sea. Its usefulness for celestial phenomena was not anticipated immediately, although people had used empty long tubes to watch stars long before Galileo’s invention. Even at the time of Aristotle, it was known that watching through a tube helped one to look at far off things more clearly. Also if one watched the sky from a pit or a well, it appeared clearer due to the
blocking of stray light.
It was the fourth night after the new Moon during the end of November 1609, when Galileo, in the backyard of his apartment in Padua, directed his telescope towards the Moon. He saw the line dividing light and darkness as something ridged, as if there were elevations and depressions on the surface of the Moon. He saw pinpoints of light sprouting in the dark region which then grew in size as if they were great mountain peaks shining in the morning sun. He was watching daybreak on the Moon!
The discovery of new lands by Columbus and other explorers based on the roundearth speculation made people believe in this model. But it was accepted that the Earth is stationary while all the stars, including the Sun, Moon and the planets revolved around it, just as it appeared to our senses. This model was given by Aristotle. All the clergy also believed in it and held it holy. In the 16th century, Copernicus gave a suncentered model in which the Moon revolved around the Earth which itself moved around the Sun. Similarly, all other known planets revolved around the Sun. The model was mathematically more elegant and calculations based on it, predicted celestial phenomena such as eclipses with far greater accuracy. But it was still regarded as only a mathematical model with little connection to reality. One of the objections was, why should only Earth have a Moon or why should there be two centers of rotation , the Earth around which the Moon revolved and the Sun around which all the planets moved?
When Galileo observed the planets through his device, he found they were globes. These were called planets after the Greek word for wanderers, as they moved against the backdrop of fixed stars. The notion of a round Earth might have given rise to the question, are these planets like our own Earth or could it be that Earth is also a wanderer? After a few months, Galileo saw some accompanying stars around planet Jupiter. There were four of them and they seemed to change their relative positions with respect to Jupiter. The known orbit of Jupiter could not explain the strange appearance of these stars until Galileo realized that they must be orbiting the planet itself, which was why sometimes they were on the west of it and at other times on the east. This was a momentous discovery, which could potentially be a rebuttal to the objections against Copernican model: it could show that other planets can have moons and also the center of rotation need not be the privilege of Earth alone.
Galileo made many telescopes and distributed them so that people themselves could verify his claims. But only about ten percent of the instruments really were good enough to show the moons of Jupiter. Other people held their prejudices and blamed the telescope itself for causing optical illusions. They acknowledged the usefulness of telescopes on land, but for sky they said it was an instrument of deception. It took some time before Galileo´s findings were corroborated by independent sources.
For two thousand years, man had regarded sky as an abode of perfect objects. With telescopes, we started to discern the universe in much greater detail and could spot imperfections in our picture of the universe. Galileo had to face the ire of the Church for challenging the established world view. He had to abandon his work and face punishment. But the telescope in due time was adopted as an essential tool in astronomy. Over centuries, the instrument has undergone tremendous changes and improvements. To this day, it continues to enhance our understanding of the structure and origin of the universe and keeps redefining our place in it.