 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Astronomical basis of the Hindu calendar" – news ·newspapers ·books ·scholar ·JSTOR(January 2022) (Learn how and when to remove this message) |
 |
| History of science and technology in the Indian subcontinent |
|---|
| By subject |
TheHindu calendar is based on ageocentric model of theSolar System.[1] A geocentric model describes the Solar System as seen by an observer on the surface of the Earth.
The Hindu calendar defines nine measures of time (Sanskrit:मानIAST:māna):[2]
Of these, only the last four are in active use[3] and are explained here.
Thecandra māna (Sanskrit:चन्द्र मान) of the Hindu calendar is defined based on the movement of the Moon around the Earth. Thenew moon (Sanskrit:अमावास्य,romanized: amāvāsya) andfull moon (Sanskrit:पूर्णिमा,romanized: pūrṇimā) are important markers in this calendar.
Thecandra māna of the Hindu calendar defines the followingsynodic calendar elements:
Apakṣa (Sanskrit:पक्ष) is the time taken by the Moon to move from anew moon to a full moon and vice versa. Thewaxing phase of the moon is known as the bright side (Sanskrit:शुक्ल पक्ष,romanized: śukla pakṣa) and thewaning phase is known as the dark side (Sanskrit:कृष्ण पक्ष,romanized: kṛṣṇa pakṣa). During apakṣa, the Moon advances 180° with respect to the Earth-Sun axis.
Acāndramāsa (Sanskrit:चन्द्रमास) is the time taken by the moon to move from a new moon to the next new moon (as per the amānta [Sanskrit:अमान्त] tradition) or a full moon to the next full moon (as per the pūrṇimānta [Sanskrit:पूर्णिमान्त] tradition).[4][note 1] In other words acāndramāsa is thesynodic period of the Moon, or twopakṣas. During acāndramāsa, the Moon advances 360° with respect to the Earth-Sun axis.
Acandra māna varṣa orlunar year is made up of 12 consecutivecandramāsa.[5] Thesetwelve candramāsa are designated by unique namescaitra,vaiśākha, etc.[note 2]
In some instances an additionalcandramāsa, known as anadhikamāsa, is added to synchronise thecandra māna varṣa with the solar year orsaura māna varṣa.
Atithi (Sanskrit:तिथि) is the time taken by the Moon to advance 12° with respect to the Earth-Sun axis.[6] In other words atithi is the time taken for the Moon'selongation (on theecliptic plane) to increase by 12°. Atithi is one fifteenth of apakṣa and one thirtieth of acāndramāsa. Atithi corresponds to the concept of a lunar day.
Tithi haveSanskrit numbers according by their position in thepakṣa, i.e.prathama (first),dvitīya (second) etc. The fifteenth, that is, the lasttithi of akṛṣṇa pakṣa is calledamāvāsya (new moon) and the fifteenthtithi of a śukla pakṣa is calledpūrṇimā (full moon).[7]
Thesaura māna (Sanskrit:सौर मान) of the Hindu calendar is defined by the movement of the Earth around the Sun.[8] It containssidereal (Sanskrit:निरयन; nirayana) andtropical (Sanskrit:सायन; sāyana) elements.
Asaura māna varṣa orsidereal year is the time taken by the Sun to orbit the Earth once and return to the starting point with respect to the fixed stars. The starting point is taken to be the position of the Sun when it is inopposition toSpica (Sanskrit:चित्रा,romanized: citrā).[9][note 3].[11]
Arāśi (Sanskrit:राशि) is a 30° arc of the orbit of the Sun around the Earth[12] (i.e an arc of theecliptic). Starting in the vicinity of Zeta Piscium (IAST: revatī), the twelve (i.e. 360° divided by 30°) rāśi are designated meṣa (Sanskrit:मेष), vṛṣabha (Sanskrit:वृषभ) etc. Asauramāsa (Sanskrit:सौरमास) is the time taken by the Sun to traverse a rāśi.[4] Sauramāsa get their names from the corresponding rāśi. sauramāsa corresponds to the concept of a month. The moment in time when the Sun enters a rāśi is known as asaṅkramaṇa (Sanskrit:सङ्क्रमण) or saṅkrānti (Sanskrit:सङ्क्रान्ति).
These time periods are defined based on thesolstices (Sanskrit:अयन;IAST: ayana) andequinoxes (Sanskrit:विषुवत्;IAST: viṣuvat).[13]
The time taken by the Sun to move from thewinter solstice to thesummer solstice is known as northward movement (Sanskrit:उत्तरायण,romanized: uttarāyaṇa) and time taken by the Sun to move from thesummer solstice to thewinter solstice is called southward movement (Sanskrit:दक्षिणायन,romanized: dakṣiṇāyana). Due to theaxial tilt of the Earth, the Sun appears to move towards the north from theTropic of Capricorn to theTropic of Cancer duringuttarāyaṇa, and towards the south from the tropic of Cancer to the tropic of Capricorn duringdakṣiṇāyana.[note 4]
The time taken by the Sun to move from thespring equinox (ecliptic longitude 0°) to theautumnal equinox (ecliptic longitude 180°) is known asdevayāna (Sanskrit:देवयान). The time taken by the Sun to move from theautumnal equinox to thespring equinox is designated aspitṛyāṇa (Sanskrit:पितृयाण). Due to the axial tilt of the Earth, the Sun appears to be in the north celestial sphere duringdevayāna and the south celestial sphere duringpitṛyāṇa. In Hindu tradition, the northcelestial sphere is consecrated to the gods (deva) and the south celestial sphere is consecrated to the ancestors (pitṛ). Devayāna and pitṛyāṇa are not in active calendric use any longer but do form the basis forpitṛpakṣa.
Aṛtu (Sanskrit:ऋतु)[note 5] is the time taken by the Sun to move sixty degrees on its orbit around the Earth.[note 6] Ṛtu corresponds to the concept of a season.
The six ṛtu of the year are known as
Nākṣatra māna (Sanskrit:नाक्षत्र मान) is defined with respect to the fixed stars, so all elements aresidereal in nature.
Adina (Sanskrit:दिन) is the time taken by the celestial sphere to complete onesidereal rotation around the Earth.[17][note 7] In reality, this movement is caused by thediurnal rotation of the Earth on its axis. This definition is not used in practice but is required for defining the following smaller units of time. Adina is ~4 minutes short of 24 hours.
Aghaṭikā (Sanskrit:घटिका) ornāḍī (Sanskrit:नाडी) is one sixtieth of a nakṣatra dina, or just under 24 minutes.
Avighaṭikā (Sanskrit:विघटिका) orvināḍī (Sanskrit:विनाडी) is one sixtieth of a ghaṭikā, or just under 24 seconds.
Aprāṇa (Sanskrit:प्राण) orasu (Sanskrit:असु) is one sixth of a vighaṭikā, or just under four seconds.[18]
Sāvana māna (Sanskrit:सावन मान) of the Hindu calendar definescivil time.
Adina (Sanskrit:दिन) is the time between two succeeding sunrises.[19] dina corresponds to the concept of asolar day. The length of adina varies withdaytime length.
Apart from the four māna explained above, the concept of nakṣatra is an important characteristic of the Hindu calendar. This term has multiple meanings:[20]
The four māna explained above are used in combination in the Hindu calendar.
adhikamāsa
As seen above, both the cāndra māna and saura māna of the calendar define a varṣa comprising twelve māsa, but the duration of the varṣa differ; the cāndra māna varṣa is shorter than the saura māna varṣa by about eleven sāvana dina. As a result, unless explicitly synchronised, these two parts of the calendar will diverge over time, as the cāndra māna varṣa will keep "falling behind" the saura māna varṣa.
In order to synchronise these two parts of the calendar, an additional cāndramāsa is introduced into some cāndra māna varṣa.[note 9] Such a cāndramāsa is referred to asadhikamāsa (Sanskrit:अधिकमास). A adhikamāsa takes its name from the name of the cāndramāsa which follows, viz. adhika āśvina precedes āśvina.
Most times every cāndramāsa witnesses a saṅkramaṇa. If a cāndramāsa does not witness a saṅkramaṇa, that cāndramāsa is designated as a adhikamāsa thus resulting in the cāndra māna varṣa "catching up" with the saura māna varṣa. This happens approximately once every two and a half (solar) years.
dina and tithi
As seen above, both the cāndra māna and sāvana māna of the calendar define the concept of a day as tithi and dina respectively. dina are not named and are not used for calendric purposes. The tithi takes precedence instead.[4][note 10]
Human life is regulated by the rising of the Sun and not by the movement of the Moon through a 12° arc. Hence, the position of the Moon at sunrise is used to determine the tithi prevailing at sunrise. This tithi is then associated with the entire sāvana dina.
To illustrate: consider the Gregorian date18th Sep 2021. Instead of referring to it as "2nd dina of kanyā masa" Hindus will refer to it as " bhādrapada māsa, śukla pakṣa, dvitiyā tithi", which is the tithi prevailing at sunrise on that sāvana dina. Even though the Moon moves into the trayodaśī arc soon after sunrise (at 6:54AM), that entire sāvana dina is considered to be dvādaśī tithi.
adhika tithi and kṣaya tithi
It is possible that two consecutive sunrises may have the same tithi, i.e. the Moon continues to remain within the same 12° arc across two consecutive sunrises. In such a case, two consecutive sāvana dina will be associated with the same tithi. The tithi associated with the second sāvana dina is referred to as aadhika (Sanskrit:अधिक) (additional) tithi.
It is also possible that an entire tithi elapses between two sunrises, i.e. the Moon traverses a 12° arc in between two sunrises (it enters the arc after one sunrise and exits the arc before the next sunrise). In this such a case, neither sāvana dina will be associated with this tithi, i.e. this tithi will be skipped over in the calendar. Such a tithi is referred to as akṣaya (Sanskrit:क्षय) (lost) tithi.
Subdivisions of a sāvana dina
Above that a nakṣatra dina is divided into ghaṭikā (of 24 modern minutes each) and vighaṭikā (of 24 modern seconds each). These same units are used to subdivide a savana dina using sunrise as the starting point, i.e. the first 24 minutes after sunrise constitute the first ghaṭikā, the next 24 minutes the second ghaṭikā and so on.
pitṛpakṣa
pitṛpakṣa (Sanskrit:पितृपक्ष) is a pakṣa during which the Sun crosses the equator and transitions overhead the southern hemisphere, i.e. theautumnal equinox occurs within pitṛpakṣa.[note 11]
bhādrapada māsa kṛṣṇa pakṣa is identified with pitṛpakṣa. This identification is not always correct. For instance, in the Gregorian year 2020, bhādrapada māsa kṛṣṇa pakṣa ended with the new moon on 17 September while autumnal equinox occurred five days later, on 22 September.
| Systems | |||||
|---|---|---|---|---|---|
| In wide use | |||||
In limited use | |||||
| Historical | |||||
| By specialty |
| ||||
| Reform proposals | |||||
Displays and applications | |||||
Year naming and numbering |
| ||||
| Fictional | |||||
