Yes, according to al-Ramli and his father, rahimahuma Allah, its wajib for the astronomer and the one who believes him. I dont know if anyone else except for al-Ramli and his father holds the view that its wajib. But Ibn al-Rif'a, al-Zarkashi and al-Subki say that its valid to fast reliying on calculations (Bughyat al-Mustarshidin)