Why do we not perform auspicious things during Ashtami and Navami? Emperuman had chosen these days to incarnate as Rama and Krishna. Are these not auspicious days despite Emperuman’s incarnation?

Based upon Astrology these days are not considered prime to do certain things, Emperuman`s incarnation and Astrology are two different aspects; just because He incarnated on these days, it does not imply these days are good. Based on Jyotisha Sastra we do not perform auspicious things.