The year 1586 in science and technology included a number of events, some of which are listed here.

Astronomy

• The last time Mercury and Venus transit the sun at the same time.^[1]

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.^[2]

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 phisicke cure, and spirituall consolation... in London.

Physics

• Galileo publishes La Billancetta, describing an accurate balance to weigh objects in air or water.^[3]
• Simon Stevin publishes De Beghinselen der Weeghconst in Leiden, discussing static forces; and De Beghinselen des Waterwichts, discussing the weight of water.

Births

• February 26 – Niccolò Cabeo, Italian polymath (died 1650)
• December 6 – Niccolò Zucchi, Italian astronomer (died 1670)^[4]
• John Mason, English explorer (died 1635)
• Giovanni de Galliano Pieroni, Italian military engineer and astronomer (died 1654)
• approx. date – Guy de La Brosse, French physician and botanist (died 1641)

Deaths

• January 9 – Paul Wittich, German astronomer and mathematician (born c. 1546)
• January 22 - Louis Duret, French physician (born 1527)
• May 29 – Adam Lonicer, German botanist (born 1528)
• June 1 − Martín de Azpilcueta, Spanish theologian and economist (born 1491)
• October 19 – Ignazio Danti, Italian mathematician and astronomer (born 1536)