應該是曆法的問題
小弟是以戊寅日為前提找出西曆日的
因此在天步大大軟體計算下是9/8日
不知天步大大軟體是採用何曆法？

Moria原作者告知應該計算無誤
http://home.comcast.net/~athomeprojects/applet_t.html

Moria uses Gregorian
calendar.

According to Moria, Greg. 685, 9/11 corresponds to Julian day UT:
1971504.6233 which matches with Astrodients (http://www.astro.com) results.
So, there is no error in the julian day computation.