Pitrupaksha is a period in the Vedic calendar when Hindus pay their respect or homage to the ancestors (Pitrus). Pitrupaksha is observed for sixteen Lunar days and during this time no auspicious ceremonies are performed.
This sixteen days of observance ends on New Moon day known as Sarvapitru Amavasya. This also falls in line with the autumn equinox. During this period, when the sun transits from the Northern to the Southern hemisphere.