What happened 1609 AD

Many of the Pilgrims who migrated to the Plymouth Plantation resided in the city of Leiden from 1609–1620, and had recorded their births, marriages, and deaths at the Pieterskerk (St. Peter's church). In commemoration, a non-denominational Thanksgiving Day service is held each year on the morning of the American Thanksgiving Day in the Pieterskerk, a Gothic church in Leiden, noting the hospitality the Pilgrims received in Leiden on their way to the New World.

Based only on uncertain descriptions of the first practical telescope which Hans Lippershey tried to patent in the Netherlands in 1608, Galileo, in the following year, made a telescope with about 3x magnification. He later made improved versions with up to about 30x magnification.

In 1609, Galileo was, along with Englishman Thomas Harriot and others, among the first to use a refracting telescope as an instrument to observe stars, planets or moons. The name "telescope" was coined for Galileo's instrument by a Greek mathematician, Giovanni Demisiani, at a banquet held in 1611 by Prince Federico Cesi to make Galileo a member of his Accademia dei Lincei.

In Milan Cardinal Federico Borromeo founded the Biblioteca Ambrosiana.

On November 30, 1609 Galileo aimed his telescope at the Moon. While not being the first person to observe the Moon through a telescope (English mathematician Thomas Harriot had done it four months before but only saw a "strange spottednesse"), Galileo was the first to deduce the cause of the uneven waning as light occlusion from lunar mountains and craters. In his study, he also made topographical charts, estimating the heights of the mountains. The Moon was not what was long thought to have been a translucent and perfect sphere, as Aristotle claimed, and hardly the first "planet", an "eternal pearl to magnificently ascend into the heavenly empyrian", as put forth by Dante. Galileo is sometimes credited with the discovery of the lunar libration in latitude in 1632, although Thomas Harriot or William Gilbert might have done it before.

The Dutch painter Judith Leyster was born in Haarlem, the Netherlands.