Solar and Lunar based Time Systems

Astronomers in ancient India had considered solar based time as the basic system of the country. They devised the prime meridian as the great circle passing through Ujjain, Kurukshetra, Lank and Meru:-

"Yallankojjayinee Puropari Kurukshethradi Desaan Sprsaan

Sutram Meru Gatam BudhaihNigatitaa Saa Madhya Rekhaa Bhuvah"- Bhaskaracharya II

The relative positions of hour circles around the world in different continents have been identified as:

"Udayo yo Lankaayaam Soasthamyah Savithureva Siddhapure

Madhyaahno Yamakotyaam Romake dese

Ardharaatram Syaat" - Aryabhata I

When it is sunrise at Lanka, it is sun set at Siddhapura (America), midday at Yamakoti (Indonesia) and midnight at Romaka deshe (Greece).

Ujjain, the centre of astronomical studies is 75 degree, 43 min east of greenwich, was accepted as International Standard Meridian only in 1883. The local time varies with places and is valid for 7.5 degrees on either side of the concerned hour circle.

Lunar based time estimation was widely used not only in India, but also middle east and south east asian countries.India had a system to correlate it with solar based system. Many of the religious practices, including astrology are based on lunar systems of time. Stellar timing does not deviate much from solar time and it is not considered significant. Morfeover, the solar and lunar observatiobs are related to the stellar background.

A lunar month has 29.5 days and lunar year is about 354.5 days. Solar year is about 265.25 days. Solar days and months are based on angle estimation. The earths orbit around the sun is elliptic and the length of arcincluded in 30 degrees geocentric segment is varying in terms of time for the motion of earth. Since the lunar year is short by about 11 days relative to solar year, it lags by 11 days every year and this accumulates to about 33 days in three solar years. In order to keep pace with solar year, Indian astronomers allowed an unadjusted balance exceeds 30 days. This additional lunar month is called 'Aadimasa' on intercalary month. This month bares the same name as the regular month and is wedged in as the 12th month and the 13th one is the regular lunar month. Aadimasa occurs at 3 years intervals.

Due to the eccentricity of earth's orbit around the Sun, the time duration of Raasi's is not uniform. Mithuna (Gemini) Raasi is of greatest duration and is about 5 Naazhika 29 Vinaazhika, Rushaba (Taurus) and Karki (Cancer) are Raasi's of more than 5 Nazhika's.

Similarly, the Raasi's Vrschika (Scorpio), Dhanu (Saggitarius), and Makara (Capricornus), are shorter than the normal. One of them is only of 29 days. Since the lunar day (Tithi) is based on the angular gap of 12 degrees between the positions if sun and moon, its duration also varies.

Due to the above variation a lunar month may be engulfed by a solar month and vice versa. In the first case when the solar month is of 32 days, a lunar month may get embedded in that solar month. Generally it occurs during Mithuna. In that solar month a lunar month starts and completes and the next lunar month starts before the end of the month. Hence the lunar month is missing in the calendar as it is indicated in the solar month at the beginning. This omitted lunar month is called Aadimaasa and the regular lunar month follows it. In this solar month there will be two new moons. The lunar month, the Aadimasa will not have a Solar Sankramanam (Eclipse). The Aadimaasa and the one that follows are known by the same name, the first one, prefixed with Aadi and later by Nija.

Another possibility is that a solar month getting engulfed in a lunar month. This is a rare case and can occur only during the shortest solar month. So in this lunar month, there will be two solar Sankramanas (Eclipse),. Such solar month is known as Kshaya Maasa. The lunar year in which this occursm there will be two Adhimaasaas. One preceeding and the other following the kshaya maasa. The first of this is called Samsarpa which is considered inauspicious. The second adhimaasa is the normal one. Intervening Kshaya Masasa is known as Amhaspati.

A similar phenomenon can also be seen in the case of solar and lunar days. A Thithi or lunar day is generally shorter than a solar day. The calendar marks the Thithi of a solar day as the one at the beginning of the solar day. Sometimes a thithi may end immediately after the beginning of the solar day and end before the end of the solar day and another thithi starts. That thithi will be the one for the next day. hence one thithi is missing in the marking of the calendar. This thithi is called Avama thithi. Which is not onsidered suitable for religious and auspicious functions.

During a shorter solar month , sometimes a thithi may be longer than the solar day. Such a thithi is called Vridhi.

Indians also designated six seasons or Rithu's. In vedic times, we find the usage of different names for solar months corresponding to the Rithu's. A Rithu is of two months duration, the table explains the details of the Rithu's  and corresponding lunar and solar month

	Rithus	Vedic Solar Months	Lunar months
1	Vasantham (Spring) (Mid March-Mid May)	Madhu and Madhav	Caithra and Vaisakh
2	Greeshmam (Summer) (Mid May- Mid July)	Sukra and Suci	Jyeshta and Aashadha
3	Varsha (Monsoon/Rainy)	Nabha and Nabhasya	Sravana and Bhadrapada
4	Sarat (Autumn) Mid Sept-Mid Nov	Eisham and Urjam	Ashwini and Karthika
5	Hemantham (fall winter) Nov-Jan	Saham and Sahasyam	Margashistha and Pausha
6	Sisira (Winter) Nov-Feb	Tapam and Tapasyam	Magha and Phalguna

Indian calendar indicates the period of agricultural activities throughout the year. They are called Njattuvela, a practice followed  in south india. They are named after 27 Nakshathra's (Star's) commencing from Ashwini of Chaithra month every year, marking the sowing period. the Njattuvela's Makayiram and Thiruvathira are supposed to be the period of heavy monsoon in Kerala. It may be noted that Indian almanac is not merely a desk calendar, but it also incorporates the time table for agricultural and religious festivals.

Compiled BVB Journal

Dr. V B Panicker