IntheGregoriancalendar,whichiswidelyusednow,theyearAD1isdirectlyprecededbytheyear1BC;ayear0doesnotexistinthissystem.Incontrast,astronomicalreckoningindeedusesayear0.Forthepurposeofdistinction,astronomicalreckoningdropsthesymbolsADandBCandusesaplusorminussignbeforetheyeari