Why is Saptami considered a powerful tithi for Shradh?

Saptami (the seventh tithi) is associated with the Sun (Surya) in Vedic astrology, and the Sun is considered the progenitor of the Manu dynasty — the ancestral lineage of all humanity. This solar connection gives Saptami a special power for ancestral rites. Additionally, the Garuda Purana identifies the central days of Pitru Paksha (Saptami through Navami) as the period when ancestors are most spiritually accessible to offerings from the living.