Galileo was born in Pisa, Italy in 1564 and he died in Florence at his house while house-arrest in 1642. Kepler was born in 1571 in a community near Stuttgart, Germany and died in 1630 during a voyage in Regensburg. They were not only contemporary but were fighting the same battle against the religious freedom at their places. Although, they both were from different Christian faiths; Galileo was a Roman Catholic and Kepler was a student of Lutheran theology at Tubingen, Germany. After coming in the contact of Tycho Brahe, Kepler became a mathematical astronomer while Galileo was an observational astronomer and he used self-made telescopes to observe the cosmic objects.

Galileo and Kepler came in to contact when Kepler sent his book “Mysterium cosmographicum” to Galilio in 1597. In response to this gift, Galileo wrote a letter to Kepler. Kepler made a hypothesis that the sun was the reason for the movement of planets. Kepler also presented some data regarding the distance and speed of the planets which later Galileo used in his manuscripts. In 1609, Kepler used the word “inertia” which was referred to the tendency of objects of being in motion if moving and in rest if are in rest in absence of external force. Kepler also hypothesized that sun is rotating on its own axis. Kepler wrote a letter to Galileo when Galileo published the “Sidereus nuncius” in which he wrote about sun as- “in the center of the world is the Sun, heart of the universe, font of light, source of heat, origin of life and cosmic motion”.

Galileo also observed the Jupiter with its four satellites. In the meantime, people started opposing ideas of Galileo and this opposition it kept growing. Religious authorities were not in condition to accept that the sun is in the centre of solar system. The earth was considered to be in the centre at that time. In the midst of these circumstances, Galileo wrote a letter to his friend Kepler, which is presented here. It seems, Galileo’s mood was not good when he wrote this letter-

Letter of Galileo to Kepler

August 19, 1610

“You are the first and almost the only person who, even after but a cursory investigation, has, such is your openness of mind and lofty genius, given entire credit to my statements…. We will not trouble ourselves about the abuse of the multitude, for against Jupiter even giants, to say nothing of pigmies, fight in vain. Let Jupiter stand in the heavens, and let eh sycophants bark at him as they will….

In Pisa, Florence, Bologna, Venice, and Padua many have seen the planets; but all are silent on the subject and undecided, for the greater number recognize neither Jupiter nor Mars and scarcely the moon as planet. At Venice one man spoke against me, boasting that he knew for certain that my satellites of Jupiter, which he had several times observed, were not planets because they were always to be seen with Jupiter, and either all of some them, now followed and now preceded him. What is to be done? Shall we side with Democritus or Heraclitus?

I think, my Kepler, we will laugh at the extraordinary stupidity of the multitude. What do you say to the leading philosophers of the faculty here, to whom I have offered a thousand times of my own accord to show my studies, but who with the lazy obstinacy of a serpent who has eaten his fill have never consented to look at planets, nor moon, nor telescope? Verily, just as serpents close their ears, so do these men close their eyes to the light of truth.

These are great matters; yet they do not occasion any surprise. People of this sort thin that philosophy is a kind of book like the AEneid or the Odyssey, and that the truth is to be sought, not in the universe, not in nature, but (I use their own words) by comparing texts! How you would laugh if you heard what things the first philosopher of the faculty at Pisa brought against me in the presence of the Grand Duke, for he tried, now with logical arguments, now with magical adjurations, to tear down and argue the new planets our of heaven.”

Source: Karl Von Gebler, Galileo Galilei, p. 26 (1879).