A solar calendar or solar calendar takes the course of the earth around the sun as the basis for dividing the time without taking the moon into account. Its base size is the tropical year (or solar year) with around 365.242 days.
The advantage of a solar calendar over a lunar calendar is that it correlates with the seasons . A shift in the seasons is prevented by the solar calendar strictly following the solar year measured between two spring points.
Since a solar year is not a whole number of days , but comprises approx. 365¼ days, a solar calendar can not only consist of common years that always have the same number of days. The necessary corrections are made by inserting leap days , whereby the exact rules of the calendar calculation are specific to the respective calendar ( intercalation ).
A solar calendar that is often used is the Gregorian calendar , which has established itself as the officially used calendar in almost all countries on earth. Of the alternatives to the Gregorian calendar, the calendar that omits the leap day every 128 years best takes the length of the solar year into account . Johann Heinrich Mädler took up this old insight in his calendar presented in 1865.
A solar calendar usually has twelve months , which refers to the phases of the moon . (Even the ancient Egyptian calendar had twelve periods of 30 days each.) The term month (etymologically related to the moon) is a relic from the older lunar calendar, the year of which is composed of 12 lunar periods ( lunations ).
So-called fiscal calendars are also usually solar calendars. Because the lunar Islamic calendar was officially in use in large parts of the Ottoman Empire , a fiscal calendar was developed with the help of which the annual tax could always be levied at harvest time.