Lunar Calendar - Commonly misunderstood simple facts

Lunar Calendar

Commonly misunderstood simple facts

Many times I have found myself in discussions where certain periods in time and certain astronomical events have been associated with their benevolent/ not so benevolent effect, depending on how these have been interpreted by the religious Gurus. Some periods that repeatedly come up in discussion are Adhik-Mass, the Intercalary month in the Lunar Calendar and Dakshinayan/ Uttrayan - The apparent movement of sun in southward or northward direction. To understand these better I picked up one book that I had read earlier and I knew had good and easy explanation of the lunar calendar - "Dating the Era of Lord Ram". The explanation below is essentially an extract from that book.

Year	Seasons ( 4 months)	Ritus (2 months)	Lunar Months	Coincides with (5000 BC)	Coincides with (As of Today)
One Year	Grisham	Vasant	Chaitra	December January	March-April
			Vaishakh	January - February	April-May
		Grisham	Jyestha	February- March	May-June
			Ashad	March-April	June-July
	Varsha	Varsha	Sawan	April-May	July-August
			Bhadrapad	May-June	August-September
		Sharad	Aswin	June-July	September-October
			Kartik	July-August	October-November
	Sheet	Hemant	Margsrish	August-September	November-December
			Paush	September-October	December January
		Sishir	Magh	October-November	January - February
			Phalgun	November-December	February- March

Lunar Calendar

Every month Indian lunar calendar begins with the first day after full moon (Krishna Paksh or decreasing phase of moon) and ends with full moon(Puranmasi)

The first month of our traditional calendar, Chaitra, begins with Shukal Paksh(First day after no moon day of Chaitra). Thus new year beings in the middle of Chaitra. The first half of Chaitra is counted in the previous year.

Everything in space is in motion. However, the closest heavenly bodies seem to be moving faster, while the far away objects seem to be still. That is the reason why the planets, sun and moon which are closer to earth seem to move while the stars seem to just be fixed in space. A group of stars is called a constellation. Entire sky is mapped using eighty-eight constellations. There are twelve constellations that are in the plane against which planets move. Each constellation occupies 30 degree of the background.

As observed earlier, as the constellations are made of stars which are very far, these constellations seem to remain fixed in the sky while the planets move in and out of them in the foreground.

The precession cycle

Actually, after 365.25 years when we count the completion of one calendar year, the earth does not come back exactly to the previous year's position in its elliptical path around the sun. Actually it takes 365 days, 5 hours, 48 minutes and 46 seconds to complete on full circle. Hence the earth falls back in its path by 0.0136 degree every year, which is 13.6 degrees every 1000 years.

Since one zodiac is 30 degrees, the earth falls back by one zodiac every 2,200 years. Since observer is on earth, the sun seems to move backward in the precession cycle by one constellation every 2,200 years. Thus due to the precession cycle, the sun would repeat its position in the same zodiac in about 25,920 years.

Nakshatras

The fastest mover in the sky is moon. It completes the round of the ecliptic in about 29 days. In other words, it travels about 12.4 degrees in the sky every day. Since one zodiac is 30 degrees, the moon stays in every zodiac for more than 2 days. But, since there is no change in the position of the planets in these two days, the uniqueness of planetary configuration for each day would have disappeared. With a view to make astronomical observations more accurate and precise, the number of constellations were further divided into 27 equal divisions, by identifying 27 prominent bright stars in the constellations, which were equidistance from each other at about 13.33 degrees.

The moon which moves 12.4 degree every day is roughly closer to one of these stars every day and therefore it is possible to ascertain its position everyday even though it remains in the same zodiac These 27 stars are called nakshatras. Therefore there are 2 or 3 nakshatras in one zodiac.

Identification of 27 nakshatras gave birth to lunar calendar. Of the 27 days, one day would be full moon day. That nakshatra, near which the full moon occurred, gave the name to the month of the lunar calendar. For example, if on the full moon day, the moon was near the star called Ashwini, that day will reckon the end of the month of Ashwin. Similarly, Vaishakh would complete on the full moon night in which the moon is near the start called Vaishakha.

Since the occurrence of a full moon day indicates the completion of a lunar month, a full moon day is traditionally called "Puran-Masi". In entire year there are 12 full moon days (barring Adhik-maas or the intercalary month) which is added after every two and a half year. On these 12 full moon days moon will always be near 12 pre-identified stars or nakshatras. Thus, the 12 months of the lunar year are named after these nakshatras.

The Nakshatras

#	Nakshatra	Other Name	Zodiac	Name of the Lunar Month
1	Ashwini	Hamal	Aries	Ashwini
2	Bharani		Aries
3	Krittika	Alycone	Taurus	Kartik
4	Rohini	Aldebaran	Taurus
5	Mrigashrira	Alnath	Taurus	Margshrisha
6	Aardhra	Althena	Gemini
7	Punarvasu	Pollux	Gemini
8	Pushya	Al Tarf	Cancer	Paush
9	Aashiesha	AsselusAustralis	Cancer
10	Maghaa	Regulus	Leo	Maagh
11	Porva Phalguni	Chort	Leo
12	Uttara Phalguni	Zavijava	Virgo	Phalgun
13	Hastaa	Porrima	Virgo
14	Chitra	Spica	Virgo	Chaitra
15	Swato	Syrma	Virgo
16	Vishaka	Zubenelgenubi	Libra	Vaishakh
17	Anooradha	Dschubba	Scorpius
18	Jyeshta	Antares	Scorpius	Jyestha
19	Moola		Sagittarius
20	Poorvashada	Nunki	Sagittarius	Ashad
21	Uttarashada	Giedi	Capricornus
22	Shravan	Deneb Algeidi	Capricornus	Shravan
23	Dhanishta		Aquarius
24	Shatabhisha		Aquarius
25	Poorva Bhadra		Pisces	Bhadrapad
26	Uttara Bhadra		Pisces
27	Revathi		Pisces

Intercalary Month or Adhik-Maas

In the sky moon completes one month in about 29 days and appears to move from one zodiac constellation to another. On the other hand, the sun also moves from one zodiac to another in about 30 days to complete a solar month. A lunar month is precisely 29 days, 12 hours, 44 minutes and 3 seconds long. Twelve such months constitute a lunar years of 354 days, 8 hours, 48 minutes and 36 seconds. The solar year, on the other hand, is of about 365.25 days. Thus, after about two and half-years the lunar years falls behind the solar year by about one full month. To help the lunar month coincide with the solar year, the practice of inserting an intercalary (extra) month or Adhik-maas was followed by the astronomers. Generally speaking, 60 solar months = 62 lunar months. Therefore, an extra month, Adhik-Maas, is inserted every 30 solar months or about every two and a half years. After about thirty solar months, there will be one solar month in which the moon will appear to move from one zodiac to another while the sun will not move from one zodiac to another. In other words, when the sun remains in one zodiac constellation while the moon completes its one lunar month from full-moon to full-moon, that lunar month is called Adhik-maas.

Uttarayan and Dakshinayan

During the summers, days become long and the nights short; while during winters, it reverses. Somewhere around March and September, the days and nights are equal. These periodic and cyclical changes take place because of apparent movement of the sun from north in the summers to southward direction and from south in the winters to northward direction. In our traditional terminology, the movement of the sun from the north to southward direction is called Dakshinayan while the reverse movement is called Uttrayan. The southern declination when the sun appears to move between Cancer and Sagittarius is called Dakshinayan. The northern declination of the sun, when it appears to move between the signs of Capricon and Gemini is called Uttarayan. The sun reaches the extreme north at around 21^st June in its cyclical movement and it reaches the extreme south at around 22^nd December. These two points are called Summer Solstice and Winter Solstice respectively. Similarly, the two equinoxes vernal and autumnal fall on 21^st March and 23^rd September respectively and they mark the days when days and nights are equal.