1609 in science

Astronomy

• July 26 – English scientist Thomas Harriot becomes the first to draw an astronomical object after viewing it through a telescope: he draws a map of the Moon, preceding Galileo by several months.
• Johannes Kepler publishes Astronomia nova, containing his first two laws of planetary motion.

Biology

• Charles Butler publishes The Feminine Monarchie, or the History of Bees, the first full-length English-language treatise on the science of beekeeping.

Exploration

• April 4 – Henry Hudson sets out from Amsterdam in the Halve Maen.
• * August 28 – Hudson finds Delaware Bay.
• * September 11–12 – Hudson sails into Upper New York Bay and begins a journey up the Hudson River.

Medicine

• Louise Bourgeois Boursier publishes Diverse Observations on Sterility; Loss of the Ovum after Fecundation, Fecundity and Childbirth; Diseases of Women and of Newborn Infants in Paris, the first book on obstetrics written by a woman.
• Jacques Guillemeau publishes De l'heureux accouchement des femmes in which he describes a method of assisted breech delivery.

Technology

• Cornelius Drebbel invents the thermostat.

Births

• June 29 – Pierre Paul Riquet, French engineer and canal builder
• October 8 – John Clarke, English physician

Deaths

• March 26 – John Dee, English alchemist, astrologer and mathematician
• April 4 – Carolus Clusius, Flemish botanist
• August 4 – Joseph Duchesne, French physician and alchemist.
• August 16 – André du Laurens, French physician and gerontologist.
• December – Oswald Croll, German iatrochemist