This is the oldest layer of Vedic astronomy, older than the zodiac's arrival in India, and it rests on something anyone can verify by looking up. Watch the Moon against the fixed stars for a month and you will see it move: a little over thirteen degrees each night, passing a different patch of sky each time, until after twenty-seven nights it is back where it began.
Twenty-seven nights, twenty-seven names
The Moon's sidereal period, the time it takes to return to the same position against the stars, is 27.32 days. Round it and you have the number.
The tradition divides the circle of the sky into twenty-seven equal segments, each of 13° 20', and calls them nakshatras. The word is usually translated as lunar mansion, which is a good description of what it is: the Moon's lodging for the night.
Each nakshatra has a name, a symbol, a presiding deity and a ruling planet. They are not abstract divisions. They are named after the star groups that mark them, and several are recognisable to anyone who knows the northern sky: Krittika is the Pleiades, Rohini is Aldebaran, Mrigashira sits in Orion's head.
The Moon, not the Sun
This is the difference that matters most for anyone coming from Western astrology, and it is a genuine difference of method rather than of interpretation.
Western astrology asks which sign the Sun was in when you were born. Twelve possibilities, each covering about thirty days, which is why everyone knows their sign and why it is the same for everyone born in a given month.
Vedic astrology asks which nakshatra the Moon was in. Twenty-seven possibilities, each lasting roughly a day, which means it changes constantly and two people born a day apart have different ones.
The Sun tells you what month you were born in. The Moon tells you what night.
That is your janma nakshatra, your birth star, and in the Indian tradition it is the more personal of the two. It has historically determined the first syllable of a child's name, and it is still consulted for marriage compatibility and for choosing the hour of anything important.
Because the Moon moves through roughly one nakshatra per day, a birth date alone gives an answer that can be wrong by one. To place it exactly you need the time and the place of birth as well, since those fix where the Moon actually stood.
Anyone who tells you your nakshatra from a date alone is giving you a good estimate, not a certainty. It is worth knowing which you are being given.
The twenty-seven
In order, beginning at the point the tradition treats as the start of the circle.
| # | Nakshatra | Symbol | Deity |
|---|---|---|---|
| 1 | Ashwini अश्विनी | Horse's head | Ashwini Kumaras |
| 2 | Bharani भरणी | The womb | Yama |
| 3 | Krittika कृत्तिकाThe Pleiades | Blade, flame | Agni |
| 4 | Rohini रोहिणीAldebaran | Cart, chariot | Brahma |
| 5 | Mrigashira मृगशिर | Deer's head | Soma |
| 6 | Ardra आर्द्रा | A teardrop | Rudra |
| 7 | Punarvasu पुनर्वसु | Quiver of arrows | Aditi |
| 8 | Pushya पुष्य | Cow's udder, lotus | Brihaspati |
| 9 | Ashlesha आश्लेषा | Coiled serpent | The Nagas |
| 10 | Magha मघा | Royal throne | The Pitrs, the ancestors |
| 11 | Purva Phalguni पूर्व फाल्गुनी | Front of a bed | Bhaga |
| 12 | Uttara Phalguni उत्तर फाल्गुनी | Back of a bed | Aryaman |
| 13 | Hasta हस्त | An open hand | Savitr |
| 14 | Chitra चित्राSpica | A bright jewel | Tvashtar |
| 15 | Swati स्वाति | Young shoot in wind | Vayu |
| 16 | Vishakha विशाखा | Triumphal arch | Indra and Agni |
| 17 | Anuradha अनुराधा | Lotus | Mitra |
| 18 | Jyeshtha ज्येष्ठाAntares | Earring, umbrella | Indra |
| 19 | Mula मूल | Bunch of roots | Nirriti |
| 20 | Purva Ashadha पूर्वाषाढ़ा | Winnowing basket | The Waters |
| 21 | Uttara Ashadha उत्तराषाढ़ा | Elephant's tusk | The Vishvadevas |
| — | Abhijit अभिजित्Vega · usually not counted | Three-cornered | Brahma |
| 22 | Shravana श्रवण | An ear, three footprints | Vishnu |
| 23 | Dhanishta धनिष्ठा | A drum | The Vasus |
| 24 | Shatabhisha शतभिषा | An empty circle | Varuna |
| 25 | Purva Bhadrapada पूर्व भाद्रपदा | Front of a funeral cot | Aja Ekapada |
| 26 | Uttara Bhadrapada उत्तर भाद्रपदा | Back of a funeral cot | Ahir Budhnya |
| 27 | Revati रेवती | A fish | Pushan |
Abhijit, the one that is left out
There is a twenty-eighth. It sits between Uttara Ashadha and Shravana, it is named after Vega, one of the brightest stars in the northern sky, and its name means victorious. Some older systems count it. Most do not.
The usual explanation is arithmetical: twenty-seven divides the circle evenly and twenty-eight does not, so Abhijit was given a very narrow span and then quietly dropped from the standard reckoning. It survives in muhurta, the choosing of auspicious times, where the Abhijit hour around midday is still considered favourable for beginning things.
A mala has 108 beads for counting and one more, the guru bead, that is never counted. Ayurveda names 107 vital points on the body and adds the mind as the 108th. The sky has 27 nakshatras and one more that is usually left out of the count.
Three times, in three unrelated systems, the number is completed by something that stands slightly outside it. We do not think this was designed. It is just what happens when a tradition keeps counting for long enough.
Twenty-seven becomes a hundred and eight
Each nakshatra divides into four quarters, called padas, meaning feet or steps. Each pada spans 3° 20', and each carries its own shading of the nakshatra's character.
Which is where the most significant number in the tradition comes from, and why a mala has the number of beads it does. The beads and the sky are counting the same thing.
What it is used for
Nakshatras are not primarily a personality system, which is the main way Westerners encounter astrology. They are a calendar of quality: a way of saying what a given moment is suited to.
A child is traditionally named with a syllable drawn from the nakshatra the Moon was in at their birth. Marriages are matched partly by comparing the birth stars of the couple. And the hour of a ceremony, a journey, a signing, or the laying of a foundation is chosen by finding a nakshatra whose character suits the act. That practice is called muhurta, and it is why a Vedic ceremony is rarely scheduled for whenever happens to be convenient.
Why we named a circle after it
Our ceremonies hold a fixed number of names: 27, 108, or 432. The mansions of the Moon, the beads of the mala, and the years of the present age, each four times the one before.
The circle of twenty-seven is the smallest we hold, and the one where a name is least likely to be lost among others. One name for each night the Moon takes to cross the sky and come home.