In acronyms, BN is the abbreviation for “before Newton”, or years before the birth of Isaac Newton, in the modern era dating system (Newtonian calendar), which occurred on 25 Dec 1642 (Old System, Julian calendar) or 4 Jan 1643 (New System, Gregorian calendar). [1]
References
1. Note: the term “before Newton” (BN) is an hmolscience alternative or rather terminology reform upgrade to the older religio-mythology based “before Christ” (BC) dating system notation.