URL: http://hindupanchang.blogspot.com/2008/03/when-to-observe-shri-ram-navami.html
Lord Ramachandra was born on Chaitra Shukla Navami, madhyanaha time, Purnavasu nakshatra and mesha surya and karka lagna.
Observance Rule: Chaitra Sukla Navami, prevailing during madhyahana time. If prevails on both days during the madhyahana kala (3/5th) of the dinmana then take the second one. If it doesn't prevails on second day during madhyahana kala but prevails on first day then take the first one otherwise take the second one.
Vaishnava rule variation: If it prevails on first day with ashtami viddha but prevails during madhyahana kala and doesn't prevail on second day during madhyanaha kala but it prevails for three muhurtha after sunrise (144 minutes) take the second day.
Explanation: The Madhyahana is the third / fifth part of the dinamana. The dinamana is the difference between sunset and sunrise on the same day. This is the total length of the day. The navami tithi should be prevailing during the 3rd fifth part of the dinamana based on local sunrise and local sunset.
According to this Smarthas can celebrate Shri Ramanavami (2008) as follows:
According to Vaishnava siddhanta:
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