Amavasai (அமாவாசை) is the new-moon day, the 30th and last tithi of krishna paksha (waning fortnight). Astronomically, it is the moment when the Moon and Sun have nearly the same ecliptic longitude (elongation ≈ 0°). It occurs once per lunar month.

Pournami (பௌர்ணமி) is the full-moon day, the 15th and last tithi of shukla paksha (waxing fortnight). Astronomically, it is when the Moon and Sun stand opposite each other (elongation ≈ 180°). It occurs once per lunar month.

Tarpanam (தர்ப்பணம்) is a water ritual honoring deceased ancestors. It is primarily performed on Amavasai days, but also during pitru paksha (the 15-day ancestor period in Purattasi month). Water, black sesame, and rice are offered with mantras for three generations of ancestors.

Is Amavasai a bad day?

Amavasai is considered inauspicious for new beginnings (weddings, contracts, travel), but it is not a 'bad' day. It is a day for introspection, ancestor rituals, and closure, rather than action and initiative. An auspicious time interval (nalla neram) can occur on Amavasai.

What is the difference between Amavasai and Pournami?

Amavasai (new moon, tithi 30) and Pournami (full moon, tithi 15) are the two opposite endpoints of the lunar month. Amavasai is for ancestor rituals and introspection; Pournami is for temple visits, worship, and celebration. Astronomically, Amavasai = elongation ≈ 0°, Pournami ≈ 180°.

When is Thai Amavasai?

Thai Amavasai falls in the Tamil month of Thai (mid-January to mid-February). It is the most important Amavasai day of the year for tarpanam. The exact date varies each year because it depends on the lunar tithi timing.

Can Pournami fall on different dates in different cities?

Yes, but it is rare. Pournami (tithi 15) typically lasts over 24 hours, so nearly all cities see it on the same date. The difference can arise when the tithi transition falls near sunrise in a particular city.

Amavasai & Pournami, new moon and full moon in panchangam · தமிழ் பஞ்சாங்கம்

Amavasai is the new-moon day (tithi 30, Moon–Sun elongation ≈ 0°) and Pournami is the full-moon day (tithi 15, elongation ≈ 180°) in the Hindu calendar. Amavasai is the day for tarpanam (ancestor rituals) and is considered inauspicious for new beginnings. Pournami is auspicious for temple visits and Vishnu/Shiva worship. Both occur once per lunar month.

The two endpoints of the lunar month

The lunar month swings between two endpoints: Amavasai (அமாவாசை), when the Moon is invisible, and Pournami (பௌர்ணமி), when the Moon is full. Astronomically, Amavasai is the moment when the Moon and Sun have nearly the same ecliptic longitude (elongation ≈ 0°), and Pournami is when they stand opposite each other (elongation ≈ 180°). In the panchangam, Amavasai is the 30th and final tithi of krishna paksha (waning fortnight), and Pournami is the 15th and final tithi of shukla paksha (waxing fortnight).

Both days carry deep ritual significance. Amavasai is 'the ancestors' day', the day for ancestor rituals. Pournami is 'the temples' day', the day for worship and full-moon lamps. Together they form the lunar month's inhale and exhale.

Amavasai, the new-moon day

Tarpanam: the ritual for ancestors

Amavasai is the regular day when Hindu families perform tarpanam (தர்ப்பணம்), a water ritual where one offers water, sesame seeds, and rice to deceased ancestors. The belief is that ancestors' souls (pitru) are closer to the earthly realm on new-moon day, and tarpanam eases their journey.

Tarpanam is typically performed at sunrise or morning, facing south (the direction of the pitrus).
Traditionally the men of the family are responsible, but in modern practice all adults perform it.
Water mixed with black sesame (ellu) and rice is offered with specific mantras for three generations of ancestors.
Thai Amavasai (January–February) is the most important tarpanam day of the year. Thousands travel to Rameswaram.
Aadi Amavasai (July–August) is the second most important, with large gatherings at rivers and the sea.
Mahalaya Amavasai (in Purattasi month, September–October) concludes the 15-day pitru paksha period.

Amavasai as an 'inauspicious' day

Amavasai is traditionally considered inauspicious for new beginnings, one avoids starting new projects, signing contracts, or holding weddings. The logic is that the Moon's total absence (darkness) symbolizes emptiness and closure. But Amavasai is not bad, it is a day for introspection, closure, and honoring those who came before.

Pournami, the full-moon day

Temple visits and full-moon rituals

Pournami is the most auspicious day for temple visits. Many temples hold special pujas, and devotees light full-moon lamps (vilakku) and perform pradakshina (circumambulation of the temple). Satyanarayana Puja, a Vishnu worship associated with prosperity, is traditionally held on Pournami.

Chithirai Pournami (April–May): Full moon in the first Tamil month. A festive temple day.
Vaikasi Visakam (May–June): When Pournami coincides with Vishakha nakshatra, Murugan's birthday.
Aavani Avittam (August): Brahmins renew the sacred thread (Upanayanam), falls close to Pournami.
Thai Pousam (January–February): Pournami near Pushya nakshatra, major Tamil temple festival.
Guru Pournami (Aashada month): Homage to the spiritual teacher.
Karthigai Deepam (November–December): Pournami in Karthigai month, lamp festival across Tamil Nadu.

Pournami and fasting

Pournami fasting is optional, it is not a mandatory viratham like Ekadasi. But many keep a light fast (fruit and milk) on Pournami and use the day for meditation and temple visits. Shiva devotees hold Pournami especially sacred, as Shiva wears the Moon in his hair.

The major Amavasai and Pournami days

Day	Month	Type	Significance
Thai Amavasai	Thai (Jan–Feb)	Amavasai	Most important tarpanam day. Pilgrimage to Rameswaram.
Aadi Amavasai	Aadi (Jul–Aug)	Amavasai	Second most important tarpanam. Gatherings at rivers and coasts.
Mahalaya Amavasai	Purattasi (Sep–Oct)	Amavasai	Concludes pitru paksha, 15-day ancestor period.
Chithirai Pournami	Chithirai (Apr–May)	Pournami	Full moon in the Tamil new year month. Festive temple day.
Vaikasi Visakam	Vaikasi (May–Jun)	Pournami	Murugan's birthday, when Pournami + Vishakha nakshatra.
Thai Pousam	Thai (Jan–Feb)	Pournami	Major temple festival. Pournami + Pushya nakshatra.
Karthigai Deepam	Karthigai (Nov–Dec)	Pournami	Lamp festival across Tamil Nadu.
Guru Pournami	Aashada (Jul–Aug)	Pournami	Homage to the spiritual teacher.

The major named Amavasai and Pournami days in the Tamil calendar.

The astronomy behind new moon and full moon

In the panchangam, Amavasai and Pournami are determined by the Moon–Sun elongation, the angular difference between the Moon's and Sun's ecliptic longitude as seen from Earth.

Day	Tithi	Elongation	What happens
Amavasai	30 (last of krishna paksha)	348°–360° (≈ 0°)	Moon and Sun have nearly the same longitude. Moon is invisible (conjunction).
Pournami	15 (last of shukla paksha)	168°–180°	Moon and Sun stand opposite each other. Moon is full (opposition).

Amavasai and Pournami in elongation degrees.

Each tithi covers 12° of elongation. Amavasai (tithi 30) corresponds to elongation 348°–360°, Pournami (tithi 15) to 168°–180°. The moment of Amavasai/Pournami is when elongation crosses 360° or 180° respectively, but in the panchangam, it is the tithi at sunrise that counts.

Amavasai/Pournami and your city

Like all tithi-based observances, Amavasai and Pournami can fall on different dates in different cities. The reason is the same: the tithi at sunrise determines the day, and sunrise varies with a city's latitude, longitude, and time zone.

Worked example

Example: Pournami in Chennai vs. New York

Suppose tithi 15 (Pournami) begins at 03:00 UTC and tithi 16 (krishna prathamai) begins at 22:00 UTC.

Chennai sunrise: 05:58 IST (00:28 UTC)
New York sunrise: 06:10 EDT (10:10 UTC)
Both cities: Same date
But if tithi 15 were shorter (05:00–08:00 UTC): Chennai 00:28 < 05:00 → tithi 14. New York 10:10 > 08:00 → tithi 16. Neither sees Pournami!

Normally all cities see Pournami on the same or adjacent days. A kshaya Pournami (skipped) is extremely rare because tithi 15 typically lasts over 24 hours.

Amavasai and Pournami in daily life

Many Tamil families keep Amavasai free from major decisions, it is a day for silence, tarpanam, and remembrance.
Pournami is the preferred day for temple visits, donation (annadanam), and starting positive habits.
Sathabhishekam (80th birthday celebration) and certain pujas are planned for Pournami.
Amavasai oil: many Tamils apply sesame oil (nalla ennai) to the body on Amavasai morning before bathing.
Fishermen and farmers still use Amavasai/Pournami for planning: high tides at full moon, better catches at new moon.

Amavasai and Pournami, new moon and full moon in the Tamil calendar

In short