1823 in science
- Olbers' paradox is described by the German astronomer Heinrich Wilhelm Matthäus Olbers.
- Cambridge Observatory established in England.
- December 29 – Great Comet of 1823 first observed.
- February 20 – James Weddell's expedition to Antarctica reaches latitude 74°15' S and longitude 34°16'45" W, the most southerly position that will be attained for more than 80 years.
- After August – Philipp Franz von Siebold begins to introduce Western medicine to Japan.
- October 5 – The Lancet founded by Thomas Wakley.
- Theodric Romeyn Beck publishes the first significant American book on forensic medicine, Elements of Medical Jurisprudence in Albany, New York.
- January 23 – In a cave on the Gower Peninsula of Wales, William Buckland inspects the "Red Lady of Paviland", the first identification of a prehistoric (male) human burial. The bones, discovered on December 21 last, are with those of the woolly mammoth, proving that the two had coexisted.
- December 10 – On the Jurassic Coast of southern England, Mary Anning finds the first complete Plesiosaurus skeleton.
- December 6 – English inventor Samuel Brown obtains his first patent for a hydrogen fuelled compressionless atmospheric gas vacuum engine, the first internal combustion engine to be applied industrially.
- First use of a Fresnel lens in a lighthouse optic, at the Cordouan lighthouse on the Gironde estuary.
- First permanent wire cable suspension bridge, Pont Saint Antoine in Geneva, by Guillaume Henri Dufour, of two 40 m spans.
- French officer Henri-Joseph Paixhans develops the Paixhans gun, the first naval artillery to fire explosive shells.
- Annals of the New York Academy of Sciences first published.
- January 3 – Robert Whitehead (died 1905), English inventor of the self-propelled torpedo.
- January 8 – Alfred Russel Wallace (died 1913), British naturalist who devises the theory of natural selection at the same time as Charles Darwin.
- February 3 – Spencer Fullerton Baird (died 1887), American ornithologist and ichthyologist.
- December 22 – Jean Henri Fabre (died 1915), French entomologist.
- January 26 – Edward Jenner (born 1749), English inventor of vaccine.
- September 23 – Matthew Baillie (born 1761), British pathologist
- date unknown - Agnes Ibbetson, English plant physiologist (b. 1757)
- Stratton, F. J. M. (1949). "The History of the Cambridge Observatories". Annals of the Solar Physics Observatory, Cambridge. 1.
- Prosser, R. B. (2004). "Macintosh, Charles (1766–1843)". Oxford Dictionary of National Biography. Oxford University Press. doi:10.1093/ref:odnb/17541. Retrieved 2011-04-23. (subscription or UK public library membership required)
- Aldhouse-Green, Stephen (October 2001). "Great Sites: Paviland Cave". British Archaeology (61). Retrieved 2010-07-16.
- Torrens, Hugh (1995). "Mary Anning (1799–1847) of Lyme; 'The Greatest Fossilist the World Ever Knew'". The British Journal for the History of Science. 25 (3): 257–284. doi:10.1017/s0007087400033161.
- Gill, T. (1826). The Technical Repository, p. 383.
- Hardenberg, Horst O. (1992). Samuel Morey and his atmospheric engine. SP-922. Warrendale, Pa.: Society of Automotive Engineers. ISBN 1-56091-240-5.
- Watson, Bruce (August 1999). "Science Makes a Better Lighthouse Lens". Smithsonian. 30: 30.
- Peters, Tom F.; Andrea L. (1987). Transitions in Engineering: Guillaume Henri Dufour and the Early 19th Century Cable Suspension Bridges. Basel: Birkhauser. ISBN 3-7643-1929-1.