Jyotiṣa — Vedic Astronomy and the Science of Sacred Time
Jyotiṣa ('pertaining to the luminaries/lights'; from jyotis = 'light, luminary, heavenly body') is the fifth Vedāṅga — the science of astronomical observation and calendar calculation that determines the correct temporal framework for all Vedic ritual and religious activity.
The Vedāṅga Jyotiṣa (the oldest surviving jyotiṣa text, c. 1400–1200 BCE) is primarily concerned with the nakṣatra (lunar mansion) system — tracking the moon's daily position through its 27 (or 28) nakṣatras as the primary calendar framework for Vedic ritual timing. The key elements of Vedic jyotiṣa include:
- Tithi (lunar day): the thirty divisions of the lunar month based on the moon's phase — each tithi has its specific ritual character (e.g., Ekādaśī is auspicious for Vaiṣṇava worship, Amāvāsya for ancestral rites)
- Nakṣatra (lunar mansion): the twenty-seven star-groups through which the moon passes — each nakṣatra has its presiding deity and ritual significance
- Yoga (conjunction): the combination of solar and lunar positions producing the twenty-seven yogas
- Karaṇa (half-tithi): the half-lunar-day divisions
- Vāra (weekday): the seven days of the week associated with the seven classical planets
These five elements together constitute the Pañcāṅgam ('five-limbed almanac') — the daily Vedic calendar that every Śrī Vaiṣṇava household and temple relies upon. The Pañcāṅgam determines: which days are auspicious for prapatti, vivāha (marriage), nāmakaraṇa (naming ceremony), and travel; when festivals fall; which thirunakshatram (Āzhvār or Āchārya birth star) is being observed.
Uveda.org's own Pañcāṅgam tool computes the Tenkalai Śrī Vaiṣṇava calendar — sunrise/sunset, tithi, nakṣatra, auspicious times (muhūrta) — using the pyswisseph astronomical library with Tenkalai-tradition calculation rules.