1586 in science

Astronomy

• The last time Mercury and Venus transit the sun at the same time.

Botany

• Jacques Daléchamps publishes Historia generalis plantarum in Lyon, describing 2,731 plants, a record number for this time.

Cryptography

• Blaise de Vigenère publishes Traicté des chiffres ou secretes manières d'escrire in Paris, describing an autokey cipher of his invention.

Exploration

• July 21 – Thomas Cavendish sets out from Plymouth in the Desire on the first deliberately planned circumnavigation.

Mathematics

• Francesco Barozzi publishes Admirandum illud geometricum problema tredecim modis demonstratum quod docet duas lineas in eodem plano designare, a treatise on the construction of parallel lines.

Medicine

• Timothy Bright publishes A Treatise of Melancholie; containing the causes thereof, & reasons of the strange effects it worketh in our minds and bodies: with the cure, and spirituall consolation... in London.

Physics

• Galileo publishes La Billancetta, describing an accurate balance to weigh objects in air or water.
• Simon Stevin publishes De Beghinselen der Weeghconst in Leiden, discussing static forces; and De Beghinselen des Waterwichts, discussing the weight of water.

Zoology

• Luis Méndez de Torres's Tratado Breve De La Cultivacion y Cura de las Colmenas first observes that hives have a queen bee and not a king as previously thought.

Births

• February 26 – Niccolò Cabeo, Italian polymath
• December 6 – Niccolò Zucchi, Italian astronomer
• John Mason, English explorer
• Giovanni de Galliano Pieroni, Italian military engineer and astronomer approx. date – Guy de La Brosse, French physician and botanist

Deaths

• January 9 – Paul Wittich, German astronomer and mathematician
• January 22 - Louis Duret, French physician
• May 29 – Adam Lonicer, German botanist
• June 1 − Martín de Azpilcueta, Spanish theologian and economist
• October 19 – Ignazio Danti, Italian mathematician and astronomer