411 REFERENCE · Wiktionary
January 0
Reference material by Wiktionary contributors. This retains its source identity and is not 411 news reporting.
English
Proper noun
December 31
Usage notes
January 0 refers to the day before January 1 in an annual ephemeris. It keeps the date in the year for which the ephemeris was published, thus avoiding any reference to the previous year, even though it is the same day as December 31 of the previous year.