What causes the change in seasons on Earth?
In the northern hemisphere, the Earth’s 23.50 tilt towards and away from the Sun during June and January causes’ summer and winter respectively. It would be the converse in the converse in the southern hemisphere.
Does the change in the Earth-Sun distance during an year have any appreciable effect upon the seasons on Earth?
No.
Do the hemispheres have identical temperatures during summer and winter?
Theoretically, the Earth should have a slightly hotter climate in the southern hemisphere compared to the northern hemisphere. However, the larger mass of ocean in the southern since the ocean heats up and to even down more slowly than land areas.
What is the Apsides Line?
The Apsides Line is an imaginary line connecting two points on the Earth’s orbit representing the dates of Aphelion and Perihelion.