Based on the height of the sun in the sky, at what time of year is it summer in the southern hemisphere? when is it winter in the southern hemisphere?

December to February

Explanation:

Based on the height of the sun in the sky (i.e. distance between the earth and the sun ) there is summer in the southern hemisphere during the the month of  December to February. The distance between the earth and sun varies because the orbit of the earth is elliptical in shape with sun at one of the center of the ellipse.This happens not only because of the distance from the sun but also the tilt of the earth affects the earth's temperature at various geographical locations. During summer the position of the earth is such that the southern hemisphere on the tilted axis of the earth receives direct sunlight which makes it relatively warmer.

Cardiac muscle causes movement in the bone.