Editing 1939 in science (section)

==Physics==
* January–February – Discovery of [[nuclear fission]] is announced independently by [[Otto Hahn]] and [[Lise Meitner]].<ref>{{cite journal|first1=O.|last1=Hahn|first2=F.|last2=Strassmann|title=Über den Nachweis und das Verhalten der bei der Bestrahlung des Urans mittels Neutronen entstehenden Erdalkalimetalle|journal=[[Naturwissenschaften]]|volume=27|issue=1|pages=11–15|date=January 6, 1939|doi=10.1007/BF01488241|bibcode=1939NW.....27...11H|s2cid=5920336 }}</ref><ref>{{cite journal|first1=Lise |last1=Meitner |first2=O. R. |last2=Frisch |title=Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction |journal=[[Nature (journal)|Nature]] |volume=143 |issue=3615 |pages=239–240 |url=http://www.nature.com/physics/looking-back/meitner/index.html |date=February 16, 1939 |doi=10.1038/143239a0 |accessdate=22 May 2011|archiveurl=https://web.archive.org/web/20110525075850/http://www.nature.com/physics/looking-back/meitner/index.html |archivedate=May 25, 2011 |url-status=live |df=mdy |bibcode=1939Natur.143..239M |s2cid=4113262 |url-access=subscription }}</ref><ref>{{cite journal|first=O. R. |last=Frisch |title=Physical Evidence for the Division of Heavy Nuclei under Neutron Bombardment |journal=Nature |volume=143 |issue=3616 |pages=276 |date=February 18, 1939 |doi=10.1038/143276a0 |bibcode=1939Natur.143..276F |doi-access=free }}</ref> On January 26, [[Niels Bohr]] reports the splitting of the uranium nucleus with a release of two hundred million electron volts of energy to a conference on the campus of [[George Washington University]] in Washington, D.C.<ref>''Announcement of the Atomic Age'' plaque next to the entrance of the Physics Department at GWU (erected 2002).</ref>
* August 2 – The [[Einstein–Szilard letter]] is signed by [[Albert Einstein]], advising President of the United States [[Franklin D. Roosevelt]] of the potential use of [[uranium]] to construct an [[atomic bomb]]. It is delivered on October 11.
* October 21 – First meeting of the [[S-1 Uranium Committee|Advisory Committee on Uranium]] under [[Lyman James Briggs]], authorised by President Roosevelt to oversee [[neutron]] experiments.