Calendars of India: Theory and Practice – Book in the Workshop

Calendars of India: Theory and Practice – Book in the Workshop

Suggestions for topics for inclusion (or exclusion) are welcome.

(This book is in the workshop. I am right now gathering materials for this book. Am looking at six to nine months for the completion of the book. Then another year for publishing it?)

A synopsis

A YouTube version is available here.

(Note that these are the first thoughts. Subject matter [and title] may undergo changes as time passes. Any suggestions in this area are welcome.)

These days, there is an upswell of interest in Indian mathematics, Indian astronomy and Indian religions, observances and festivals. Most of these observances and festivals are celebrated on particular dates of one calendar or the other. For example, the birthday of Lord Rama, one of the most important deities of veneration among Indians, is celebrated on the ninth day of the bright half of the month of Chaitra. What does that mean?

In India, while we follow the western (Gregorian Calendar) for civil and official purposes, at home, for religious and liturgical purposes we follow a myriad of calendars based on the region we are in, based on our religion, our community etc.. This gives rise to many questions that an average person is faced with:

  • Why is Lord Krishna’s birthday celebrated on different dates in different parts of India? Why even in the same place, Iyers and Iyengars have different dates for Krishna’s birthday?
  • Why do we hear people saying “While my actual birthday is today, my birth star / birth tithi is next week” What does it mean when someone says my birth star is today?
  • Do time zones make a difference to the star you are born under? [That is, does a person born at the same instant in the US and in India fall under the same star, tithi etc?]
  • Why is Makar Sankranti which is supposed to be the start of Uttarayana, celebrated nearly 24 days after the actual event of the start of Uttarayana? What is Uttarayana?
  • Why are there so many year-beginning dates in India? How many “new-years” are there in India and why?
  • How are months reckoned in the various calendars? Why do some months in some calendars have 32 days?
  • What is the concept of an added month? That is, why do some years have 13 months? And rarely only 11 months?
  • How do Christians fix the date of Easter?
  • Why does the Muslim festival of Ramadan migrate across the seasons? That is, why does Ramadan come sometimes in summer and sometimes in winter?
  • Why do Shraaddhas (death anniversaries)  and birthdays of the same star or tithi fall on different days?
  • What are the five “limbs” of the Panchanga? And what is the significance of each of those?
  • What is Raahu Kaala? And why is it bad? What are the other Kaalas?
  • What is a “muhurta”? What do we mean when we say that the “muhurta” for a wedding is such and such a time?
  • What is the meaning of a birth chart and how do you cast it?
  • Does the day begin at sunrise, sunset or any other time?
  • What is the effect of an eclipse?
  • What is Kali Yuga and Kali day number?
  • What is the history of the calendar?
  • What is the astronomy behind calendars?
  • What are the various calendars followed in India and how are they organised?
  • What is the meaning of a solar calendar, a lunar calendar, a luni-solar calendar etc?
  • Why don’t we have leap years in Indian calendars?
  • Why are there 30 tithis but only 27 stars?
  • What is yoga in the panchanga?
  • Why is there a difference between the beginning and ends of the birth signs (Aries, Taurus etc.) between western and Indian systems?

These are some of the kinds of questions that people of India grapple with every day when it comes to celebrating any religious festival.

This book Calendars of India: Theory and Practice strives to answer all the above questions and do much more.

The first part of the book looks at the origin of calendars and how calendars are intimately tied to the positions of the Sun, the Moon and the planets. It then goes into the astronomy of calendars, touching upon the following, among others:

  • The Solar System – the revolution of the earth round the sun, the movement of the sun, the moon and the planets as seen from the earth; 
  • The rotation of the earth – time, reckoning of days and hours minutes etc.
  • Sunrise, sunset, equation of time, mean solar day, sidereal day
  • Coordinate systems, the ecliptic, celestial equator, equinoxes, solstices; precession of the equinoxes and ayanamsa; obliquity of ecliptic, nutation etc. etc.
  • The year, days from equinox to equinox, the tropical year, the anomalistic year, the sidereal year etc
  • Days of the week
  • The sky, the stars, constellations, signs, the path of the ecliptic, the position of the sun
  • The moon, position of the moon, the phases of the moon and Eclipses
  • Notes on Indian astronomy, the various siddhantas (Surya Siddhanta, Brahma Siddhanta and Arya Siddhanta) and the various karanas associated with them, 
  • Epochs, Julian Day and Kali Yuga and Kalidina.
  • The changing sky and star orientations over the ages.

The second part looks at the Gregorian Calendar, its evolution and the logic behind it with respect to the astronomy discussed in the first part. The Gregorian calendar serves as a baseline for looking at other calendars. It also looks at the history of calendars.

The third part looks at the basic logic of Indian calendars and how the astronomical facts discussed in the first part affect them. Some of the topics discussed in this part are:

  • Types of calendars and the logic behind them – Solar calendars, lunar calendars, luni-solar calendars, equal-month calendars etc.
  • Solar months – stars, day numbering/naming, sankranthi, rule for beginning a month
  • Lunar months – Amaanta (new-moon last) and Puurnimaanta (full-moon last) systems, half-months/pakshas, tithis, day numbering/naming, month names, added (adhika) months, suppressed (kshyaya months), day additions, day suppressions, day repetition, length of months, adhika, kshaya tithis etc.
  • Lunisolar month 
  • Yuga, kalpa, mahayuga etc. samvatsaras, cycyles, kshaya and adhika samvatsara jupiter cycle
  • Mentioning dates; 10th day of the 8th month or 10 days after 8 months. Count up from the first of the month (like we do now) or count down to an event (like the roman counted to the ides etc.)

The fourth part looks at the various calendars of India and how they are organised:

  • the various Indian Panchangas and calendars – Kollam era, tamil era, vikrama era, saka era, gupta, bengali, Kannada/Telugu era, oriya, muslim era, maratha and many more
  • Calendars during the Vedic times
  • Chinese calendar, iranain calendar
  • Mathematical calendars (computed purely mathematically) and astronomical calendars (based on the position of the sun, moon etc.) ; Observational calendars (based on sighting of moon etc.)

The fifth part looks at the mathematics and astronomy (not predictions!) behind the astrological systems of India

  • Birth charts, Rashis (signs), positions of the planets, what is Rahu and Ketu, What is Gulika etc. effect of time zones
  • Navamshas and other amshas
  • What is ascendant (lagna)
  • What is the meaning of houses, aspects etc.
  • What is retrograde motion of planets?
  • What are muhurtas (times, good times etc.), Raahu kaala and other kaalas etc. dashas; balance of dashas

As I mentioned before, these are initial thoughts. As I get more and more into details of the book, subject matter and the order and format they are presented in may change.

One thought on “Calendars of India: Theory and Practice – Book in the Workshop

  1. Please send your newsletters, book publication details and all other information to my mail id


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