Why are there four seasons alternating? How are the seasons formed?

The reasons for the alternation of seasons are as follows:

1 and the formation of the four seasons are the result of the earth's revolution around the sun. The earth has been spinning from west to east and revolving around the sun from west to east. The orbit of the earth's revolution is an ellipse, and the sun is always in a focus. In the continuous revolution of the earth, the included angle between the earth axis and the revolution orbit is always 66 34', that is, the earth always revolves around the sun obliquely.

2. Because the earth's axis is tilted when it rotates, its spatial orientation remains unchanged, so the situation that the earth's surface is irradiated by the sun at different positions in the orbit of revolution is not exactly the same, which causes the direct point of the sun on the earth's surface to change, thus producing four seasons.

For example, in the northern hemisphere, around the summer solstice, the ground gets more sunlight and heat, forming summer. Around the winter solstice, the ground gets less sunlight and heat, forming winter. Around the vernal equinox and autumnal equinox, the ground gets less sunlight and more heat than in summer, forming spring and autumn respectively. The seasons in the northern and southern hemispheres are opposite.