Telescope earliest existing record of a telescope was a 1608 patent submitted to the government in the Netherlands by Middelburg spectacle maker Hans Lippershey for a refracting telescope. The actual inventor is unknown but word of it spread through Europe. [[Galileo Galilei|Galileo]] heard about it and, in 1609, built his own version, and made his telescopic observations of celestial objects. The idea that the [[Objective (optics)|objective]], or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using [[parabolic reflector|parabolic mirrors]]—reduction of [[spherical aberration]] and no
Adriaan Metius and developed a special form of Jacob's staff. In 1585, his father had estimated the ratio of a circle's circumference to its diameter, later called pi, to be approximately . Metius later published his father's results, and the value is traditionally referred to as Metius' number. The lunar crater Metius is named after him. In Vermeer's painting "The Astronomer" (1668), the book lying on the table has been identified as a 1621 second edition of Metius's "Institutiones Astronomicae Geographicae". It is opened to Book III, where "inspiration from God" is recommended for astronomical research along with knowledge of geometry and