In the Hindu calendar, the day starts with the sunrise. It is allotted five "properties" or "limbs", called aṅgas. They are:
the Tithi (one of 30 divisions of a synodic month) active at sunrise
the Vāsara (ancient nomenclature), vāra (modern nomenclature), like in ravi-vāra, somā-vāra, etc. or weekday
the Nakṣatra (one of 27 divisions of the celestial ecliptic) in which the moon resides at sunrise
the Yoga (one of 27 divisions based on the ecliptic longitude of the sun and moon) active at sunrise time
the Karaṇa (divisions based on tithis) active at sunrise.