2009: The International Year of Astronomy
Astronomers are celebrating the 400th anniversary of the birth of modern observational astronomy in 2009. The International Year of Astronomy commemorates Galileo Galilei's first use of the telescope to study the night sky in 1609. He discovered that the surface of the Moon is rough, that the Milky Way consists of a vast number of stars, that Venus shows phases, and that moons orbit Jupiter.
His discoveries confirmed that Earth is not the center of the universe and demonstrated that the universe is both vast and dynamic -- discoveries that revolutionized human understanding of the cosmos and our place in it.