Because the Earth is rotating about its axis in the same sense as its orbit, the side that is rotating toward the Sun is the side that is at that time facing forward in the direction of the Earth's motion in its orbit.
(the Earth; is rotating; about its axis in the same sense as its orbit) (the side; is rotating; toward the Sun) (the side that is rotating toward the Sun; is; the side that is at that time) (the side; is; at that time) (that time; facing; forward; in the direction of the Earth's motion in its orbit)
the Earth the side the side that is rotating toward the Sun the side that time
is rotating is rotating is is facing
about its axis in the same sense as its orbit
toward the Sun
the side that is at that time
at that time
forward in the direction of the Earth's motion in its orbit