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Nakshatra (Sanskrit: ???????, IAST: Nak?atra) is the term for lunar mansion in Hindu astrology. A nakshatra is one of 28 (sometimes also 27) sectors along the ecliptic. Their names are related to the most prominent asterisms in the respective sectors.
The starting point for the nakshatras according to Vedas is "Krittika" (it has been argued because the Pleiades may have started the year at the time the Vedas were compiled, presumably at the vernal equinox), but, in more recent compilations, the start of the nakshatras list is the point on the ecliptic directly opposite to the star Spica called Chitr? in Sanskrit, which would be Ashvin?, an asterism that is part of the modern constellation Aries, and these compilations therefore may have been compiled during the centuries when the sun was passing through the area of the constellation Aries at the time of the vernal equinox. This version may have been called Mesh?di or the "start of Aries".
The first astronomical text that lists them is the Vedanga Jyotisha.
In classical Hindu scriptures (Mahabharata, Harivamsa), the creation of the nakshatras is attributed to Daksha. They are personified as daughters of Daksha and as wives of Chandra known as the Moon God (who reluctantly married the 26 other nakshatra's on Daksha's request even though he was only interested to marry Rohini), or alternatively the daughters of Kashyapa, the brother of Daksha.
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In the Atharvaveda
In the Atharvaveda (Shaunakiya recension, hymn 19.7) a list of 28 stars or asterisms is given, many of them corresponding to the later nakshatras:
This 27-day time cycle has been taken to mean a particular group of stars. The relationship to the stars really has to do with the periodicity with which the Moon travels over time and through space past the field of the specific stars called nakshatras. Hence, the stars are more like numbers on a clock through which the hands of time pass (the moon). This concept was discovered by Dr. Jessie Mercay in her research on Surya Siddhanta.[4]
List of Nakshatras
The classical list of 27 nakshatras is first found in the Vedanga Jyotisha, a text dated to the 600-700 BCE. The nakshatra system predates the Hellenistic astronomy which became prevalent from about the 2nd century CE.
In Hindu astronomy, there was an older tradition of 28 Nakshatras which were used as celestial markers in the heavens. When these were mapped into equal divisions of the ecliptic, a division of 27 portions was adopted since that resulted in a cleaner definition of each portion (i.e. segment) subtending 13° 20' (as opposed to 12° 51 3/7’ in the case of 28 segments). In the process, the Nakshatra Abhijit was left out without a portion.[5]:179 The Surya Siddhantha concisely specifies the coordinates of the twenty seven Nakshatras[5]:211
It is noted above that with the older tradition of 28 Nakshatras each equal segment would subtend 12.85 or 12 degrees 51'. But the 28 Nakshatra were chosen at a time when the Vedic month was recognised as having exactly 30 days. In India and China the original 28 lunar mansions were not equal. Weixing Nui provides a list of the extent of the original 28 Nakshatras expressed in Muhurtas (with one Muhurta = 48 mins). Hindu texts note there were; 16 Nakshatras of 30 Muhurtas, 6 of 45 Muhurtas, 5 of 15 Muhurtas and one of 6 Mahurtas. The 28 mansions of the 360 degree lunar zodiac total 831 Muhurtas or 27.7 days. This is then described as an inaccurate estimate of our modern sidereal period of 27.3 days. But using the ancient Indian calendar with Vedic months of 30 days and a daily movement of the Moon of 13 degrees this early designation of a sidereal month of 831 Muhurts or 27.7 days is very precise. (The exact figure should be nearer 27.692308 but 27.7 is near enough). ref Nui Weixing and Jiang Xiaoyuan, 'Astronomy in the Sutras translated into Chinese'. Later some Indian savants dropped the Nakshatra named Abhijit to reduce the number of divisions to 27, but the Chinese retained all of their original 28 lunar mansions. These were grouped into four equal quarters which would have been fundamentally disrupted if it had been decided to reduce the number of divisions to 27. Irrespective of the reason why ancient early Indian astronomers followed a Vedic calendar of exactly 12 months of 30 days it was this calendar and not a modern calendar of 365 days that they used for the astronomical calculations for the number of days taken for the Moon to complete one sidereal cycle of 360 degrees. This is why initially they named 28 Nakshatras on their lunar zodiac.
The following list of nakshatras gives the corresponding regions of sky, following Basham.[6]
