Astronomers around the world are preparing for three days of intense sky-watching in honour of Galileo.
Galileo began observations 400 years ago with a two-lens telescope that eventually led him to discover the four main satellites of Jupiter.
He also realised Earth's Moon is pitted with craters and not a perfect sphere and revolutionised the understanding of the cosmos.
More than 1000 public events are being held in about 70 countries.
