August 25, 2009--Galileo Galilei peers at the cosmos through a telescope circa 1620, as seen in a modern drawing. (History buffs take note: The carved ebony-and-ivory mounting, now a famous part of Galileo's telescope, was actually made in 1677.)

Just over 400 years ago, Galileo--then chair of mathematics at Italy's University of Padua--got word that Dutch glass makers had invented a device that allowed viewers to see very distant objects as if they were nearby.

The mathematician soon acquired a Dutch instrument, and on August 25, 1609, he presented an improved, more powerful telescope of his own design to the senate of the city-state of Venice. The government officials were so impressed with Galileo's telescope that they rewarded the professor with a higher salary and tenure for life at his university.

At the time, Galileo was touting the telescope for commercial and military applications, such as watching ships at sea. But in the fall of 1609 Galileo turned his telescope to the heavens, setting into motion a new kind of science: telescopic astronomy.

--Victoria Jaggard

More Galileo's Telescope 400th Anniversary Coverage

• GALILEO'S TELESCOPE AT 400: Facts, Myths, More
• TELESCOPE TIME LINE: From Galileo to Hubble
• GALILEO'S "DAUGHTERS": Today's Telescopes in Pictures
• BLOG: Galileo's Telescope Helps Kick Off 100 Hours of Astronomy