The summer and winter seasons in a year are caused by

The primary cause of the summer and winter seasons is the revolution of the Earth around the Sun while maintaining a fixed axial tilt of approximately 23.5 degrees relative to its orbital plane [5]. This inclination, known as obliquity, ensures that different hemispheres are tilted toward or away from the Sun at different points in the Earth's annual orbit [1]. When a hemisphere is tilted toward the Sun, it experiences summer due to more direct solar rays and longer daylight hours; conversely, the hemisphere tilted away experiences winter [4]. While the Earth's distance from the Sun varies between perihelion and aphelion, this distance change is relatively small and is not the cause of seasonal variations [4]. Rotation on the axis merely causes day and night, while the combined effect of revolution and axial tilt drives the seasonal cycle [5].

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 12: Earth, Moon, and the Sun > 12.2.2 Seasons on the Earth > p. 177
2. [3] Science-Class VII . NCERT(Revised ed 2025) > Chapter 12: Earth, Moon, and the Sun > 12.2.2 Seasons on the Earth > p. 178
3. [5] https://spaceplace.nasa.gov/seasons/
4. [4] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 19: The Motions of The Earth and Their Effects > Lunar Nodal Cycle > p. 266