The auroral zone is defined by the last field line from the Earth that returns to the Earth. If the field of the earth extends no further than 10RE in the sunward direction, at what angle (in degrees) in the picture above does the last field line that returns to the earth on the sunward side leave the polar regions of the earth at 1RE, assuming that the fields are always described by r=R0sin2(θ)? In the drawing, this is equivalent to asking what is the angle with respect to the vertical of a line from the center of the earth to the point that the red curve intersects the light blue circle.