…Our understanding of the universe changed for ever. On August 25th 1609 an Italian mathematician called Galileo Galilei demonstrated his newly constructed telescope to the merchants of Venice. Shortly afterwards he turned it on the skies. He saw mountains casting shadows on the moon and realised this body was a world, like the Earth, endowed with complicated terrain. He saw the moons of Jupiter—objects that circled another heavenly body in direct disobedience of the church’s teaching. He saw the moonlike phases of Venus, indicating that this planet circled the sun, not the Earth, in even greater disobedience of the priests. He saw sunspots, demonstrating that the sun itself was not the perfect orb demanded by the Greek cosmology that had been adopted by the church. But he also saw something else, a thing that is often now forgotten. He saw that the Milky Way, that cloudy streak across the sky, is made of stars.

From The Economist.

Nice to see that Google is also honouring the anniversary.