A solar year or tropical year is defined as the number of days it takes for the Earth to complete one cycle around the sun. This is usually measured in terms of one of four solar events . Short years occur when the calendar year is shorter than the solar year . When this occurs, the date of a solar events in one year arrives before the solar event occurs in successive years. Phrased another way, the solar events occur on a later date on the calendar in successive years.
Long years occur when the calendar year is longer than the solar year .
When this occurs, the date of a solar events in one year arrives after the solar event occurs in successive years. Phrased another way, the solar events occur on an earlier date on the calendar in successive years. A.U.C. is the representation used by the Romans for identifying years. 1 A.D. is the same as the year 753 A.U.C. . Coincidentally, a year divisible by 4 in the Roman calendar is also divisible by 4 in the Christian calendar.