What is the time difference between a lunar and a solar year?
A solar year has 365 days. A lunar year has 354 days, and is based on twelve complete moon phase cycles or lunation.
Are all calendars based on the solar year?
No. Some calendars (such as those of the Mohammed am era) are based on the lunar year.
What is an astronomical year?
An astronomical year (also known as sidereal year) for a planet is the time taken by the planet to make a complete revolution around the Sun. In the case of the Earth, the sidereal year is equal to 365.2564 mean solar days or 365 days 6 hours 9 minutes and 9.5 seconds.