You must have seen calendars giving the months, the weekdays and the dates. If you want to find out the weekday corresponding to some date in a particular month, you can find it out by looking at the calendar. But the calendar you have come across is of only one type (starting from January and ending in December). In general, a calendar is a system of reckoning the beginning, the end and the divisions of the year.
People belonging to different lands and of different faiths have different types of calendars. In India there were two systems of calendars namely
(i) luni-solar calendar and
(ii) solar
Luni-solar system is followed in most regions of India.
LUNI-SOLAR SYSTEM
In Luni-solar system, months & years are calculated from the moon's movement with respect to the sun. There are two types of luni-solar calendars in existence. In Andhra, Karnataka, Maharashtra and Gujarat one has the Amanta system. In this, the lunar month (Chandra maasa) begins with the tithi Pratipad of Sukla paksha (the day after new moon) and ends with the next Amavasya. It is called the Amanta system because it ends with an Amavasya. So, in Amanta system the Chandra maasa begins when the angle between the sun and the moon is zero and ends after it increases to 360o. In the Poornimanta system which is mainly followed in the North India, the month begins with the tithi Pratipad of Krishna paksha (the day after full moon) and ends with the next Poornima and hence the name. So, it starts when the angle between sun and the moon is 180o and ends when it again becomes 180o. Chaitra Krishna paksha in the Poornimanta system corresponds to Phalguna Krishna paksha in the Amanta system. But Chaitra Sukla paksha means the same thing in both the systems. This is because Poornimanta maasa begins with the Krishna paksha Pratipad but Amanta system begins with the Sukla paksha Praatipad.
Click here to see the relation between the two systems
The year in Amanta system starts with tithi Pratipad of Sukla paksha in Chaitra maasa and ends with the Phalguna Amavasya. According to the nomenclature of the Poornimanta system, the year in the Poornimanta system begins with the Chaitra Sukla Pratipad and ends with the Chaitra Amavasya. Each lunar year is given a name: Prabhava, Vibhava, ... Akshaya. There are 60 names that repeat themselves after 60 years.
Chaitra Sukla Pratipad is the day following Amavasya immediately before the instant when the sun enters the Asvini nakshatra, which is around April 14th. For example, in the year 1986, Chaitra sukla Pratipad fell on April 10th. This marked the beginning of the lunar year akshaya. The last day of the lunar year was on March 29th, 1987, which was phalguna Krishna Amavasya (Amanta) or Chaitra Krishna Poornima (Poornimanta).
That year had only 354 days. The lunar year Vibhava started on March 18th, 1988 and ended on April 5th, 1989. The length of the year was 384. This was due to the adddition of an adhika maasa after Vaisakha.
SOLAR CALENDAR
This system of calendar is based on the position of the sun relative to the stars. As the sun moves along a circular path called the ecliptic and it takes 365 1/4 days to complete one revolution. This period is taken as the solar year. In the solar calendar, the year starts when the sun reaches a particular point in the ecliptic which is a constellation of stars called Mesha.
This will be around April 14th of the year. The solar year will end when the sun reaches the same point after completing a revolution (i.e.) after travelling through 360o along the ecliptic. The solar year is divided into 12 months. During a solar month, the sun travels 30o along the ecliptic, that is 1/12th of a circle. In most parts of India, the names of the solar months are the same as that of the lunar months, but to differentiate from them a prefix of Saura is added. So Saura Vaisakha is the solar month of Vaisakha. A solar month consists of 30 or 31 days normally. The solar year begins with Saura Vaisakha around April 14th.
Click here to see the names of solar months in some other parts of India
Before ending this section, we'll have a look at some of the Indian festivals and see when they occur.