Lunisolar Calendar:A calendar system that is based on both the moon's phases and the sun's position, requiring the addition of intercalary months to maintain alignment with the solar year.
Leap Year: A year in the Gregorian calendar that has 366 days instead of the usual 365, with an extra day added as an intercalary day on February 29th.
Tropical Year:The amount of time it takes for the Sun to return to the same position in the cycle of seasons, which is approximately 365.2422 days, necessitating the use of intercalary months to keep calendars aligned.