Subject: When was the reason for the seasons first known.

The seasons are the consequence of the earth's axis of rotation tilted 
with repect to the plane of its orbit around the sun. When was this 
knowledge first generally known among educated people? I guess the 
question is more about when it was generally known that the earth orbits 
the sun and that the axis of the earth's rotation is not perpendicular to 
the plane of its orbit. 

Re: When was the reason for the seasons first known.