How do I know if my ancestor died under Magha Nakshatra?

You can verify this by checking the death date and time against a traditional Hindu Panchang (almanac). The Panchang lists the nakshatra for each day and time. A knowledgeable pandit can help you check historical Panchang records to determine if Magha Nakshatra was active when your ancestor passed. If you cannot verify, perform their Shradh on Sarva Pitru Amavasya (October 10, 2026).