Pañcāṅga means "five limbs" — pañca, five, and aṅga, limb. A panchang is not a calendar in the Western sense. It is a description of a moment in five independent measurements, and each limb answers a different question.
The five limbs
1. Tithi — the lunar day
The Moon's angular distance from the Sun, in twelve-degree steps; thirty to a lunar month. This is the limb most observance depends on, and it is set out in full in what a tithi is.
2. Vāra — the weekday
The seven weekdays, each named for a graha: Ravi (Sun), Soma (Moon), Maṅgala (Mars), Budha (Mercury), Guru (Jupiter), Śukra (Venus), Śani (Saturn).
The order is the interesting part, because it looks arbitrary and is not. Arrange the seven grahas by apparent orbital period, slowest to fastest: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon. Assign them in that repeating order to the twenty-four hours of a day, each hour ruled by one graha. Whichever graha rules the first hour gives the day its name. Step forward twenty-four hours and you land three places along the list — and stepping three at a time through that sequence produces exactly the weekday order the whole world uses. The Hindu, Greco-Roman and modern Western week share this structure.
3. Nakṣatra — the Moon's asterism
Which of the twenty-seven divisions of the ecliptic the Moon occupies. Where the tithi measures the Moon against the Sun, the nakshatra measures it against the fixed stars — two independent readings of the same body. See how to read a nakshatra.
4. Yoga — the combined figure
The least familiar limb. Add the longitude of the Sun to the longitude of the Moon and divide the result into arcs of 13°20'. There are twenty-seven yogas, with names such as Vishkambha, Priti, Ayushman and Siddhi. It is a single number describing the Sun and Moon together rather than either alone, and it is used mainly in muhurta.
5. Karaṇa — the half-tithi
Each tithi divides into two karanas, so there are sixty in a lunar month, drawn from a set of eleven names. Four of the eleven are sthira (fixed) and appear once each per month; the other seven rotate. Also principally a muhurta instrument.
What a panchang is for
Two things, mostly.
Observance — establishing which day a tithi-based festival or fast falls on. Muhurta — selecting a time to begin something, by finding a moment whose five limbs are jointly favourable for the act in question. Varahamihira's Bṛhat Saṁhitā and the later muhurta literature are largely concerned with exactly this.
Note what a panchang is not. It is not a horoscope and it says nothing about an individual. It describes a moment in time as it applies to everyone at a given place.
Why two panchangs disagree
They usually agree about the astronomy and differ about the conventions, of which there are three main ones.
- Ayanamsa — the offset between the sidereal and tropical zodiacs. Lahiri is the Indian government standard; other schools use slightly different values.
- Location — sunrise, and therefore which tithi is current at sunrise, depends on where you are.
- The rule for assigning a tithi to a day — sunrise, midday, moonrise or the relevant watch of the night, depending on the observance and the tradition.
Two panchangs applying different conventions to identical astronomy will print different dates, and each is right within its own system. This is the single commonest source of confusion about Hindu festival dates.
What AdiVeda does and does not publish
AdiVeda explains the five limbs. It does not publish a daily panchang, compute tithis, or generate festival dates or muhurtas — deliberately, and permanently.
Anything of that kind has to be computed for a specific place with a stated ayanamsa and a stated rule set, and it has to be maintained every year. A site that publishes a date it cannot stand behind is worse than a site that explains the system and points you to a source that can. Where you need dates, use a panchang that names its conventions.
Where this comes from
The five-limb structure and the definitions of each limb are standard in the classical jyotisha and calendrical literature, principally the Surya Siddhanta and Varāhamihira's works. The hora-lord derivation of the weekday order is classical and is the same argument found in Greek and Latin sources. The observance conventions are living tradition and genuinely vary.