A solar year is calculated based on the movements of the sun, whereas a lunar year is based on the movements of the moon. Compared to a lunar calendar, a solar calendar is widely used across the globe. The difference in the period between a solar year and a lunar year is called an epact. One epact is 11 days.
A lunar year is a period of 12 lunar months. A lunar month can also be defined as the time the moon takes to pass through each of its phases (new moon, half moon and full moon) and return back to its original position. A solar year is the time period required for Earth to complete one revolution around the sun. One twelfth of a solar year is known as a solar month.
A lunar year has approximately 354 days. A solar year has 365 days. There is an 11-day difference between one solar year and one lunar year. This difference is called one epact. Over the course of 33 years, there will be a lag of one year between solar and lunar calendars.
A solar calendar is commonly used all over the world. However, Muslims and Jews follow a lunar calendar. Islamic calendars, otherwise known as Hijri calendars, are based on the lunar cycle, and its year consists of 12 lunar months. The Hijri calendar is mainly used for religious purposes and the Muslim religious festivals are based on this calendar. A Jewish calendar is primarily lunar and each month begins on the new moon. A Chinese calendar is a lunisolar calendar, a combination of a lunar calendar and a solar calendar.
Because there is an 11-day difference between a solar year and a lunar year, an extra (13th) month is inserted into the lunar calendar every three years. In the solar calendar, there is a leap day added to the month of February every four years.