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Our planet’s seasons are not determined by the planet’s distance from the Sun because the difference between the planet’s aphelion and perihelion is actually very small. Nor are they caused by the Earth’s rotation. The seasons are actually caused by the tilt of the planet’s axis. Earth is tilted at a 23.5° angle causing different regions of the Earth to receive varying amounts of sunlight during the year.
When the upper half of the planet is tilted toward the Sun, it is summer in the Northern Hemisphere and winter in the Southern Hemisphere. To be exact, the Earth does not actually move and tilt towards or away from the Sun. As the Earth orbits the Sun though the northern and southern halves alternate being inclined to the Sun. Thus when the Southern Hemisphere is inclined towards the Sun, it is winter in the Northern Hemisphere and summer in the Southern Hemisphere.
The seasons are not the same for different regions though. The equator does not experience seasons in the same sense; its seasons are not caused by the tilt of the Earth’s axis because the equator is in the middle of the planet and receives almost the same amount of sunlight throughout the year. Instead, it is affected by the tropical rain belt (ITCZ), which brings the rainy season. The North and South Poles experience two long seasons, summer and winter. During winter in the poles, the Sun stays down for months at a time; there is no sunlight for about 182 days during the winter in the North Pole. During the summer at the poles, the Sun is up for months straight.
Temperature changes are also due to the angle of the Sun hitting the Earth. During the summer solstice in the Northern Hemisphere, the Sun is higher in the sky causing more sunlight to hit that hemisphere. The days are also longer during this period; both of these factors make summer warmer. During the winter solstice in the Northern Hemisphere, the Sun is longer in the sky, so less sunlight reaches the planet’s surface. This is also why the days are shorter in winter, and this causes winter to be colder. The seasons are opposite in the different hemispheres, so when it is the summer solstice in the Northern Hemisphere it is actually the winter solstice in the Southern Hemisphere. Temperature is also influenced by ocean currents, winds, and other factors.
Astronomy Cast has an episode on the Earth that you will enjoy.