Tithi Praveśa
Vedic Lunar Birthday · Pañcāṅga · Muhūrta
Positions are computed entirely in your browser from a truncated solar/lunar theory (Meeus-Schlyter series, ≈1-2′ of arc) with the Lahiri (Chitrapākṣa) ayanāṃśa - typically within 2-5 minutes of Swiss-Ephemeris timings for tithi and nakṣatra boundaries. Muhūrta windows follow the classical tables of the Muhūrta Chintāmaṇi tradition, scaled to the real sunrise-sunset span of the place.
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The outer ring is the twelve-fold rāśi circle with the natal Sun and Moon marked by dashed gold rings; the inner ring carries the twenty-seven nakṣatra mansions. The terracotta wedge at the centre is the living tithi - the angle from Sun to Moon - and it is exactly what the little Moon inset lights up.
Drag the slider forward. Near day 27.3 the Moon returns to its natal mansion (sidereal return) but the tithi has drifted; near day 29.5 the tithi returns but the Moon lodges elsewhere (synodic return). Only once a year do both line up - that is the Praveśa.
Seen from Earth, the Sun traces one fixed circle through the stars each year - the ecliptic. The Moon travels nearly the same road, about 13× faster. Every position on this circle is a mile-marker from 0° to 360°, and almost everything in the Pañcāṅga comes from just these two moving points and the angle between them.
Try it below: drag the slider to move time forward from a new moon. Watch the terracotta angle grow ~12° per day, the Moon hop one mansion per night, and the phase inset track the angle exactly.
One circle, three grids
Twelve rāśi of 30° each give the solar year its bones. Twenty-seven nakṣatra of 13°20′ give the Moon a lodging for every night. And the tithi - the angle between the two luminaries divided by 12° - gives the lunar day its name.
Nothing here is symbolic decoration: each name is a statement about a measurable angle. That is why the calendar can be recomputed for any year, any place, from first principles.
The circle is divided into 12 equal arcs of 30°, each named for the constellation behind it (♈ Meṣa, ♉ Vṛṣabha, …). A rāśi is an address, not an object: “Sun in Mithuna” means its mile-marker lies between 60° and 90°. The Sun crosses one rāśi per month - which is why there are twelve months. Twelve is where the solar and lunar rhythms meet: the Moon completes ~12 cycles while the Sun completes one.
The same circle carries a finer grid of 27 mansions of 13°20′, matched to the Moon's 27.3-day lap - one lodging per night. Each is anchored to a real star (Rohiṇī = Aldebaran, Kṛttikā = the Pleiades, Chitrā = Spica). Your janma nakṣatra is simply the mansion the Moon occupied at your birth; each divides into 4 pādas of 3°20′.
A tithi is not a place but a relationship: the angle from Sun to Moon. At Amāvasyā the angle is 0°; it grows ~12° per day, and each 12° slice is one tithi - 30 lunar days per cycle. At 180° the Moon is fully lit: Pūrṇimā. The Moon's shape and the tithi are the same fact: the angle determines the phase. Because tithi is an angle, the elliptical orbits' varying speeds are absorbed automatically - real tithis run ~19 to 26 hours.
Pañcāṅga means five limbs - five readings of the same sky: Tithi (Sun–Moon angle ÷ 12°), Vāra (weekday, sunrise to sunrise), Nakṣatra (the Moon's mansion), Yoga (the sum of Sun and Moon positions in 27 divisions), and Karaṇa (half a tithi). Four of the five are pure Sun–Moon geometry.
A Hindu birthday is a configuration, not a date: your birth tithi recurring while the Sun is back in its birth rāśi. The angle alone repeats every 29.5 days - but the combination happens once a year, usually within a few days of the Gregorian birthday (twelve lunar months run ~11 days short of a solar year). That annual moment is what the Calculator tab finds.
- Jean Meeus, Astronomical Algorithms (Willmann-Bell) - the classic reference for Sun/Moon position mathematics.
- Paul Schlyter, How to compute planetary positions - the truncated lunar series used here.
- P.V.R. Narasimha Rao, Vedic Astrology: An Integrated Approach - includes the Tithi Praveśa technique and its use in annual charts.
- Pt. Sanjay Rath - tradition and articles on Tithi Praveśa (srath.com).
- Panchangam Calculations - tables of Amṛta Ghaṭikā, Varjyam and Durmuhūrtam used for the muhūrta section.
Sidereal positions use the Lahiri (Chitrapākṣa) ayanāṃśa. The teaching wheel above uses mean motions; the Calculator uses true ephemeris positions throughout.