The apparently confusing Hindu calendar, like the Chinese one, is a Luni-solar Calendar i.e. uses a combination of the Sun and Moon unlike the Western, purely Solar, Calendar or the Islamic Calendar which is based solely on the Moon. See figure below.
Broadly speaking there are two types of Calendars :
(1) Solar Calendar – follows the movement of the earth around the sun. Since the earth takes 365.25 days to complete one rotation around the sun, every four years a leap year is added where an additional day is created to correct this natural phenomenon.There are two types of solar calendars namely
(a)Tropical solar calendars – based on time taken by the sun to go from Spring Equinox to Spring Equinox. Since this does not take into account the declination (precession of the equinoxes – see end of article for a detailed description of this phenomena), this calendar is drifting apart from the actual astronomical position of the Sun in the skies. The Gregorian and the ancient Zoroastrian calendars are tropical solar calendars.
(b)Sidereal solar calendars – also follow the movement of the sun around the earth but in Hindu astronomy/astrology the earth was kept as the central observational point hence it is the apparent movement of the sun (being a star it is fixed) as observed from the earth. Hence it is the time taken by the sun to go from one fixed star to the same fixed star. The precession of the equinoxes is not applicable because fixed stars have been used. One sidereal year is roughly equal to 1.0000385 tropical years. Hence every 72 years the two calendars drift apart by one day. The Tamil, Bengali, Malayalam, Thai calendars are sidereal solar calendars.
(2) Luni-solar calendars – Many of the most ancient cultures or religions like the Hebrew, Buddhist, Chinese, Japanese, Korean etc. (some of the pre-Islamic and pre-Christian calendars too) follow the Luni-solar calendar, which indicates both the moon phase and the time of the solar year. If the solar year is defined as a tropical year (time taken by the sun to go from Spring Equinox to Spring Equinox) then the calendar will give an indication of seasons. Examples are Chinese and Hebrew calendars (Tropical Luni-solar calendars). If it is taken as a sidereal year (time taken by the sun to go from one fixed star to the same fixed star) then the calendar will predict the constellation near which the full moon may occur. Examples are Hindu and Buddhist Calendars (Sidereal Luni-solar calendars).If you study the diagrams below, we can see that because of the tilt of the earth of 23.5 degrees we get seasonal variations. When the earth is faced away from the sun along its ecliptic we get the winter season and when the tilt is towards the sun we get summer season. Autumn and spring are when the earth is evenly facing the sun.
The movement of the sun as observed from earth according to the seasons.
Hindu Calendars – Firstly it is important to understand that India being a big country almost the size of Western Europe in landmass and population lends itself to many regional variations. Secondly to understand it’s ancient timetable we must understand the moon more than the sun. The moon has two phases, ascending moon cycle (Shukla Paksh) and the descending moon cycle (Krishna Paksh) each for a period of 14.75 days hence taking a total of 29.5 days to traverse 12 fixed zodiac star/signs far away in the sky. It stays in each sign (for example Aires) for 2.45 days. The cycles of the moon give rise to Full Moon (Poornima) and New/No Moon (Amavaysa).
The 12 signs are further divided into 27 Nakshatras (again fixed stars). There are 360 degrees in a circle. Hence each Nakshatra is basically 13” 20 min (360” /27) just like each sign is 30” (360”/12). The Moon stays in each nakshatra for approximately 24 hours. The lengths of all nakshatras are not even, some being longer and some shorter. Since 12 months of 29.5 days constitute a lunar year of 354.3 days. The solar year on the other hand is 365.25 days. Thus after every 2.5 years or 30 solar months the lunar year falls behind the solar year by about a month (lunar year is 11 days less than the solar year). To help the lunar year coincide with the solar year the practice of inserting an extra month known as Adhik-Maas (extra-month) became prevalent. One of the most ancient and respected texts of India, The Rig Veda speaks of 12-13 months in a year with a clear mention of an extra month. A 28th Nakshatra called Abhijit is added in the sidereal Capricon as an extra nakshatra to tally the two systems.
The Hindu months are therefore named after the Nakshatra, which falls closest to a full moon (see figure below – for a detailed month wise break up of dates).
Hence the year is divided into two halves and there are six seasons. When the sun enters Capricon (Makara) on 14th January it starts moving northward (Sanskrit: Uttarayaana) towards the Tropic of Cancer and the second half when it starts its southward journey (Sanskrit: Dakshinayana) towards the Tropic of Capricorn when it enters Cancer (Kark) on 16th of July. There is no concept of Solstice because the calendars are not based on seasons but on fixed stars.
This date remains almost constant with respect to the Gregorian calendar. However, precession of the Earth’s axis (called ayanamsa) causes Makara Sankranti to move over the ages. A thousand years ago, Makara Sankranti was on 31 December and is now on 14 January. According to calculations, from 2050 Makar Sankranti will fall on January 15. The day usually begins at dawn, or just before, according to which astronomical and astrological systems are used.
There are broadly four different types of calendars in India. The Western and Northern parts of India use a Luni-Solar Calendar whereas the South, Bengal and Punjab/Haryana use a solar calendar. In North India (including Punjab and Orissa), the month generally begins with the full moon (Purnimanta), in Western/South India with the new moon (Amanta). See diagram below for the corresponding dates for the year 2014 for the various calendars of India. The solar Tamil calendar stands out for using the name of the nakshatra, which appears closest to the full moon of the previous month. Hence though the names of the months are the same the dates are different.
There are various ways of reckoning the New Year; most common is the day after the new moon in the month of Chaitra or, in Gujarat, the day after the Diwali new moon. This too varies according to the region. See diagram below.
Various eras are used for numbering the years; the most common are the Vikrami Era, beginning with the coronation of King Vikram-aditya in 57 BCE and the Shaka Era, counting from 78 CE. In rituals the priest often announces the dates according to KaliYuga. For these three systems, the year 2000 corresponds to 2057, 1922, and 5102 respectively, though the last figure is subject to some debate. See chart above for details. The national calendar was an attempt by Nehru to standardize all regional calendars into one. Though he might have had good intentions since it followed the Sayana system (Tropical) and not the Nirayana system (Sidereal) it was not accepted by the public of India.
This diagram puts into perspective the various regional variations of the Indian Calendar with respect to the fixed solar months/signs.
Below: The diagram shows the Hindu year, with months and the corresponding festivals. It is somewhat approximate, as the exact dates change yearly relative to the Gregorian calendar – with a month between the earliest and latest possible dates. A few festivals are determined by the sun alone, and their Gregorian dates are the same (or within one day) each year.
Precession of the Equinoxes
The actual historical zodiac of twelve star-groups is now 23 degrees off from the dates currently used by western astrologers. Astrology in the West has become more of myth and hence there is a lack of interest to talk about it scientifically. Originally there was no separation between astrology and astronomy. The ancients made astrological deductions based on their observation of the stars in the sky night after night, sleeping only at daybreak.
The path the earth revolves around the sun is called the ecliptic. The Earth is tilted in space at an angle of 23 ½ degrees. Hence the equator which divides the earth into two halves is also at 23 ½ degrees to the ecliptic. We experience seasonal changes on places other than the Tropics (within 23 ½ degrees) because of this tilt. A Certain group of stars are on 8 degrees either side of the ecliptic, that circle of stars is called the zodiac, which in Greek means “circle of animals”.
Since the total circle is 360 degrees, the star groups were divided into groups of approximately 30 degrees, making 12 groups of zodiacal signs. Over 24 hours, each group is on the eastern horizon for approximately 2 hours (24 / 12). If at the time you were born someone looked at eastern horizon and saw which constellation was rising (one cannot see the stars with naked eye in the day because of the intensity of the sunlight), that is your Lagna or Rising Sign (Body). The constellation in which your Moon was placed at that moment is your Rashi or Moon Sign (Mind) and the constellation in which your Sun is placed is your Sun Sign (Soul). In popular lingo when someone asks you, “What is your zodiac sign?” They are referring to Western (Tropical) Sun Sign. In the Vedic system more importance is given to Rashi or Moon Sign than even the Sun Sign.
The earth has three movements in total (see diagram 1). (1) Spinning around its axis – 24 hours (2) Orbit around the Sun – approximately 365 days (3) Precession – wobble like a spinning top – 25,920 years to complete one circle.
There are two visible results from this shift. The first is a gradual change in the Pole Star. Our current Pole Star, Polaris, is less than 1 degree from true north. In the year 150 B.C., it was 12 degrees 24 minutes from it. It was not until the 15th century that Polaris could be used for navigation as an indicator of true North. In 13,000 years from now, the Star Vega will be our new Pole Star. (See diagram 2)
The other result is called the Precession of the Equinoxes. The earth is changing its relation to the fixed stars. Instead of the same group of stars being with the Sun on the first day of spring, the days move backward through the zodiac. Some ancient Indian texts speak about “Spring” taking place in October or even in the month of July. That means Vernal equinox (Spring equinox; Day and Night are equal), on 21st March, occurs in one constellation for about 2,160 years (25,920 years/ 12 signs). Right now we are in the age of Pisces at 6 degrees of Pisces. Since the movement is backwards, in another 400 years, we will enter the Age of Aquarius.
The Greek astronomers had calculated the Precession of the equinoxes correctly back then but since 1,750 years have passed, Spring Equinox does not occur in Aries but Pisces. Western/Tropical Astrologers are still using the old Greek reference point, which has little to do with astronomical evidence. See Diagram below.
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