As listed in the errors section, Hypatia couldn't have known from the observational equipment available to her that the earth's orbit was an ellipse rather than a circle, (which is a special case ellipse). It was the work of Kepler using the very precise measurements of Tycho Brahe that proved that the earth's orbit is in fact an ellipse, however the deviation from a perfect circle is very minute.
The seasons are caused by the tilt of the earth's axis 23.5 degrees with respect to the ecliptic, the plane that contains the earth's orbit. In the northern hemisphere, in the summer, the northern hemisphere is tilted at a better angle, thus the warmer weather. The opposite for wintertime. The earth is actually closer to the sun in the winter than summer due to the earth's orbit being a (nearly circle) ellipse.
The seasons are caused by the tilt of the earth's axis 23.5 degrees with respect to the ecliptic, the plane that contains the earth's orbit. In the northern hemisphere, in the summer, the northern hemisphere is tilted at a better angle, thus the warmer weather. The opposite for wintertime. The earth is actually closer to the sun in the winter than summer due to the earth's orbit being a (nearly circle) ellipse.