Lunar and Solar Calendars

Calendar helps us to organize our days for social, religious, administrative or commercial purposes. Time periods like months or years in a calendar are generally synchronized with the motion of the sun or the moon. People from different civilizations and different regions have designed calendars to suit to their particular needs.

There are different types of calendars such as Lunar calendars, Solar calendars and Luni-Solar calendars. We will discuss about the Lunar and solar calendars here. Solar calendars are based on the motion of the Earth around the Sun. Its dates indicate the position of the earth on its revolution around the sun. Solar calendar accurately indicates the seasons.

The solar year has about 365.24 days and it is adjusted to 365 days. To reconcile the extra quarter day, a day is added to a common year of 365 days once in about every four years. The extra day added, is called as a leap day and the year is called as Leap year.

The Gregorian calendar, which we commonly use, is a solar calendar. It is internationally accepted civil calendar.

A lunar calendar is based on cycles of the moon phase. On an average, the length of the lunar month is 29.5 days. Therefore, in twelve months, there are only 354 days, unlike 365 days in a Solar year. A feature of purely lunar calendar is that the calendar it cannot be linked to the seasons. It drifts each year by 11 days (12 days in case of leap year) in relation to the Solar year. It comes back to the position with the solar year approximately in every 33 Lunar years.

Islamic calendar is the only widely used purely lunar calendar. It is mainly used for religious purposes. It is also used for commercial purposes in Saudi Arabia.

Generally, most of the lunar calendars, except the Islamic, are luni-solar calendars. In luni-solar calendars, months are based on a lunar cycle, but extra days are added to bring the lunar cycles into synchronization with the solar year.