My upcoming book on Indian Calendars

Happy to say that I am making good progress with this project. I am titling the book

Conversations with Āryabhaṭa: about Indian Calendars (and Astronomy) 

(any comments on the title?)

I hope to complete the writing of the book in the next 3 to 4 months. The book should run to around 80,000 words. It will have a lot of figures, so it may go to between 300 and 400 pages.

Will keep you informed on progress.

Here is a table that gives a schema of the book.

Calendar Category / Description	Calendar Mechanism / Description	Calendars Discussed	Reference (for the reader)
Empirical (Observational)    Direct visual observation: The immediate, real-time sighting of natural phenomena	Phenological / Ecological    Dynamically track the physical, organic rhythms of the local ecosystem (monsoons, winds, flora blooming, animal migrations and the stars).	Calendars of the Chola Naikens; Gonds; Santalis; Ao Naga; Khasi; Baiha; Birgor; Juang; Soligas; Todas; Nicobarese	Chapter 2
	Stellar    Track time and seasons by observing the rising and setting of specific stars or constellations relative to the night sky.	Some ancient Vedic calendars,   Santhal and Munda calendars,   Calendars of the Gond people, the Oraoan and the Toda people.	Chapter 3
	Solar / Horizon Astronomy    Synchronize with the Sun based on its observed position relative to physical, geographic landmarks on the horizon (solstice markers)	Megalithic stone circles in India (e.g., Brahmagiri sites, Hanamsagar).	Chapter 4
	Lunar    Mark time and months by the first visual sighting of the new crescent moon in the night sky	The Hijri Calendar	Chapter 5
	Lunisolar    Synchronize with both the Sun and the Moon based on direct observation of their physical positions and seasonal markers.	Ancient Vedic Calendar	Chapter 6
	Planetary    Align with the repeating orbital geometries of the planets based on systematic, recorded sky sightings	Bṛhaspati Saṃvatsara Cakra	Chapter 7

Calendar Category / Description	Calendar Mechanism / Description	Calendars Discussed	Reference (for the reader)
Algorithmic (Arithmetic / Rule-based)	Synchronizes with the tropical (Sayana) Sun or the Moon using a fixed mathematical formula and pre-programmed cycles, ensuring absolute calendar predictability.	The Tabular Hijri Calendar  Indian National Calendar  The Gregorian Calendar	Chapter 8
Ephemeris (Calculational)    True celestial coordinates. Precision calculations of shifting planetary orbits	Lunisolar    Synchronizes with both the sidereal (Nirayana) Sun and the Moon based on their calculated positions	Some Pañcāṅgas  Śaka Varṣa (Sauracāndramāna), Vikrama Saṃvat, Śālivāhana Śaka, Yudhiṣṭhira Era, Kali Yuga Era, Nepāla Saṃvat, Lakṣmaṇasena Era, The Saptarṣi Calendar	Chapter 10, 11
	Solar (Sidereal)    Synchronizes with the sidereal (Nirayana) Sun based on its calculated position	Some Pañcāṅgas,   Kollam Era (Malayāḷam), Tamiḻ (Sauramāna), Oḍiā, Vaṅgīya (Bengali), Asamīyā, Punjabi (Nānakśāhī Solar), Cālukya Vikrama Era. The Sāyana Śaka Calendar	Chapter 10, 12
	Solar (Tropical)    Synchronizes with the tropical (Sayana) Sun based on its calculated position	The Sāyana Śaka Calendar, Tārīkh-i-Ilāhī.	Chapter 13
Linear / Epochal (Continuous Count)    Unbroken tally of days. Pure, uninterrupted sequence from a fixed starting point.	A running tally of days from a fixed epoch, completely unanchored from the immediate tracking of any single heavenly body.	Kaliyuga Calendar (Ahargaṇa), Julian Day Calendar	Chapter 14

I am also thinking of adding 3 other chapters: About Time and Timekeeping in India (Chapter 15); Indian Astrological Systems (Chapter 16) (Only the theory, nothing about predictions); Some non-Indian calendars (Chapter 17) (if size allows).

You will see that Chapter 1 and 9 are missing in the above schema. Chapter 1 is (as you would have guessed) an introduction called Calendrical Questions. Chapter 9 is on astronomical calculations: It gives details of how positions of the Sun, the Moon and the planets are calculated by modern methods, by early western methods and early Indian methods.

Your comments on the above and your pointers to what is missing and need to be added are welcome.

The Vedic months – Twelve plus intercalary and suppressed months:

Here’s the Prologue to the book:

It was in the twenty-eighth year of the reign of Emperor Bhāskara Ravi Manukulāditya that Śaṅkara’s father was murdered, stabbed through his left eye. Now, though five years had gone by, Śaṅkara could not forget it. He knew, deep inside, that Kṛṣṇa had done the foul deed. No one, including Kṛṣṇa, disputed the fact that he did have a strong motive. But Śaṅkara could not prove that he had the opportunity. Kṛṣṇa had an iron-clad alibi. 

Śaṅkara’s father had been killed on the first of the month of Siṁha (Ciṅṅaṁ as they called it in Malabār where he lived). Some of the people in his village thought that they had seen Kṛṣṇa lurking around Śaṅkara’s house that morning. But the headman of Kṛṣṇa’s village, about ten miles north of Śaṅkara’s village, was certain that Kṛṣṇa was in their village the whole day of the first of Ciṅṅaṁ. In fact, he had asked Kṛṣṇa to run some errands for him and he had seen Kṛṣṇa many times that day. And who was Śaṅkara to question the word of the headman? 

But Śaṅkara could not let go. He wanted to be sure. He decided that he would question Kṛṣṇa one last time. And if Kṛṣṇa’s story checked out, he would drop the issue from his mind once and for all. He therefore sent word to Kṛṣṇa to come and meet him on the fifteenth of that month. 

Kṛṣṇa did not keep the appointment. Śaṅkara waited the whole day, but Kṛṣṇa did not come. Śaṅkara was furious, but what could he do? 

However, the next day, come lunch time, there was Kṛṣṇa at Śaṅkara’s house asking for him. 

Śaṅkara said, “I thought I asked you to come yesterday?” 

Kṛṣṇa said, “No, your messenger said the fifteenth.” 

Śaṅkara felt like he had been hit by a bolt of lightning. It all made sense now. He now knew for sure that Kṛṣṇa had indeed killed his father. Kṛṣṇa had no alibi at all. 

Śaṅkara had not paid close attention to the calendars…