Galileo�s telescope, 1610.

ITALY - FEBRUARY 15: This is a replica of one of the earliest telescopes made by Galileo Galilei (1564-1642) after he learnt of the invention of the telescope in 1608. This refracting telescope magnifies only 14 times and gives a very restricted field of view. As a result Galileo was only able to view about a third of the Moon through his telescopes. However, despite these limitations, Galileo published �Sidereus Nuncius� ('The Starry Messenger') in 1610, which describes the celestial sights he saw with his new telescope. These included craters on the Moon, the phases of Venus and the moons of Jupiter. This facsimile was made in 1923 at the Museo di Fisica e Storia Naturale, in Florence, Italy where the original still resides. (Photo by SSPL/Getty Images)