M_night tprime 3600 t_night tprime 3600 t_day M_day rem time_ 3600 1 day_length km M M_c c -1 M k T T_a kb kinc T T_b T_b delta_T 2 T_b delta_T 2 M_b T_b T_a kb kinc T_day T_b T_day T_a kb kinc T_night T_b T_night T_a