Panchanga

The Vedic almanac of a day — its five 'limbs': tithi (lunar day), nakshatra (Moon's mansion), yoga, karana, and vaara (weekday). Four are computed from the Sun and Moon; it's the basis of Muhurta, electional timing.

Panchanga (पञ्चाङ्ग, 'five limbs') is the traditional Hindu almanac. Four of its five limbs come straight from the positions of the Sun and Moon: the tithi (lunar day) from their elongation in steps of 12°, the nakshatra from the Moon's sidereal position, the yoga from the sum of their sidereal longitudes in steps of 13°20', and the karana as the half-tithi (steps of 6°). The fifth, the vaara, is simply the weekday. Because the tithi and karana depend only on the angle between the Sun and Moon, they're the same whichever zodiac you use; the yoga and nakshatra are read in the sidereal zodiac. Together they describe the quality of a day, and they are the raw material of Muhurta — choosing an auspicious time to begin something. The limbs are exact astronomy. Which tithi, yoga, or karana is considered favourable for which activity is interpretive tradition, not a measured effect.

Not: The panchanga is not a forecast of what will happen on a day. It is a description of the lunar-solar sky for that date. The 'good day / bad day' judgments layered on it are convention, not a property of the day itself.

The five limbs are computed exactly, but they shift through the day (a tithi can change at any hour), so a single daily value is a snapshot. The auspicious/inauspicious meanings are traditional convention.