Q1.
I have noticed that we go through a cycle of seasons every year. Is it related to the revolution of the Earth around the Sun in some way?
Answer
Yes — but the revolution alone is not enough. Seasons happen because of the revolution together with two other facts: the Earth's axis of rotation is tilted with respect to its orbit, and the Earth is spherical.
The Earth keeps its tilt pointing the same way all through the year. So as it travels round the Sun, first one hemisphere and then the other leans towards the Sun.
| Month | Northern Hemisphere | Sunlight it receives | Season there |
|---|---|---|---|
| June | Tilted towards the Sun | More intense, and for more than 12 hours a day | Summer |
| December | Tilted away from the Sun | Less intense, and for less than 12 hours a day | Winter |
Why the tilt matters: because the Earth is a ball, the same bundle of sunrays is spread over a smaller patch in the hemisphere leaning towards the Sun, so that patch is heated more; in the other hemisphere the same bundle spreads over a larger patch and heats it less. The tilt also puts more than half of the leaning hemisphere in the lit half of the Earth — which is why days are longer in summer than in winter, exactly as the girl in the picture noticed. More intense sunlight, lasting longer, adds up to summer.
Key point: the seasons of the Southern Hemisphere are the reverse of ours — June is winter and December is summer in Australia.