January 0

January 0

January 0 is an alternative date for December 31. January 0 is the day before January 1 and after December 30 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 (Jan 0, 1900 is the same as Dec 31, 1899). January 0 also occurs in the epoch for the ephemeris second, "1900 January 0 at 12 hours ephemeris time". 1900 January 0 (at Greenwich Mean Noon) was also the epoch used by Newcomb's Tables of the Sun, which became the epoch for the Dublin Julian day.