Panchang or Panchangam is a lunisolar Hindu astrological calendar/almanac that presents important astronomical data including days & dates, months, auspicious moments (muhurtas), eclipses, lunar phases, zodiacal occurences etc., Panchangam is typically used to check various Hindu festivals and auspicious times (muhurtas). Very simplistically the months are calculated according to the revolution of moon. There are mainly two types of calendars/almanacs; the Shaka calendar followed in south India and Maharashtra and the Vikrama calendar followed by the rest of India and Nepal. The origins of the Hindu Calendar are in the Rig Veda around 3 BC.
According to the Shaka calendar, the month begins with the first day after new moon. The Vikrama calendar months begin the first day after the full moon. The 15 days as the moon grows and becomes full moon is referred to as “Shuddha or the "Shukla Paksha”. The full moon is the Poornima. The next 15 days as the moon wanes is referred as “Krishna Paksha”. New moon is the Amavasya. A date is called as the “Tithee”.
There are seven days in a week; Ravi-vaar (Sunday or the day of sun), Som-vaar (Monday or the day of the moon), Mangal-vaar (Tuesday or the day of Mars), Budha-vaar (Wednesday or the day of Mercury), Guru-vaar (Thursday or the day of Jupiter), Shukra-vaar (Friday or day of Venus) and Shani-vaar (Saturday or day of Saturn).
The elliptical orbit of the earth is divided into 27 nakshatras or fixed stars. The nakshatra in which the moon lies in at sunrise is the nakshatra for the day. There are 12 zodiacs corresponding to the 27 nakshatras.
They are Mesha (Airies), Vrushabh (Taurus), Mithun (Gemini), Karka (Cancer), Simha (Leo), Tula (Libra), Kanya (Virgo), Vrishchika (Scorpio), Dhanu (Sagittarius), Makar (Capricorn) , Kumbha (Aquarius), Meen (Pisces).
The twelve lunar months correspond to when the Sun transits to each of the 12 zodiacs beginning with Mesha or Aeries.
- Chaitra (sun transits into Mesha or Aries)
- Vaishākh (sun transits into Vrushabh or Taurus)
- Jyaishtha (sun transits into Mithun or Gemini)
- Āshādha (sun transits into Karka or Cancer)
- Shrāvana (sun transits into Simha or Leo)
- Bhaadra or, Bhādrapad (sun transits into Tula or Libra)
- Āshwin (sun transits into Kanya or Virgo)
- Kārtik (sun transits into Vrushchika or Scorpio)
- Agrahayana or, Mārgashīrsha (sun transits into Dhanu or Sagittarius)
- Paush (sun transits into Makar or Capricorn)
- Māgh (sun transits into Kumbha or Aquarius)
- Phālgun(sun transits into Meen or Pisces)
These 12 months account for 356 days. A solar year has 365 or 366 (leap year) days. To compensate for the 9-10 days, there is an extra month called the Adhik Masam every 32.5 months
A typical Panchang tabulates positions of the Sun, the Moon and other planets for every day of the year on a fixed place (longitude, latitude) and time of day (in 24-hour format IST). The users calculate the remaining data using their relative difference from this fixed place and time.
The casting of a Panchang involves elaborate mathematical work involving high level of spherical geometry and sound understanding of astronomical phenomena, including movements of heavenly bodies. In practice, the tabulation is done on the basis of short-cut formulations as propounded by ancient Vedic sages and scholars.
‘Panchanga Sravanam’, listening to the recitation of the almanac is a common custom on the day of Ugadi ie., Kannada & Telugu New Year. It is a social gathering where a priest or an elderly, respected person in the community refers to the calendar and presents a general forecast about the upcoming year.