The United Nations Organisation (UNO) following a global scheme laid out by the International Astronomical Union (IAU) has declared the year 2009 as the International year of Astronomy to commemorate and celebrate the important occasion just 400 years back, when Galileo invented the first astronomical telescope in 1609 and instantly turned it around to heavens. The year is intended to be a global celebration of astronomy and its contributions to society and culture, stimulating worldwide interest not only in astronomy but science in general, with a particular slant towards young people. Galileo’s astronomical discoveries and investigations into the Copernican theory have led to a lasting legacy which includes the categorisation of the four large moons of Jupiter discovered by Galileo as the Galilean moons. It was an important milestone in the field of astronomy and of science in general. Till that discovery, science was mostly theoretical and speculative. It was the beginning of a new era of science, that of acquiring knowledge through observation and experimentation. In this article, we shall try to explore, in brief, the important achievements in the field of astronomy during last 50 years.