Answer:
The varying Sun-Earth distance and Earth's rotation cause this phenomenon.
Step-by-step explanation:
Heating of the Earth: A fun fact is that the Earth does not revolve around the sun in a perfect circular path, but instead it revolves in a ellipse path (like an oval shape). This phenomenon would explain Summer and Winter periods. Since the sun is more inclined to one side of the oval, as the Earth gets closer to the same side of the oval, it also gets closer to the Sun, absorbing much more heat, causing higher general temperatures in which we call it Summer. The vice versa could also be explained when the Earth is getting further away from the Sun.
Hours of daylight: We know that the Earth rotates around its axis at an angle of about 23.5 degrees. Now, imagine this. The axis never changes directions no matter the position of the Earth when it revolves around the Sun. During Summer, most continents are directly facing the Sun, projecting more sunlight on a larger surface area. As such, it would take a longer time for the Earth to rotate itself away from the sunlight, causing longer hours of daylight. The vice versa could also be explained when the Earth is further away and generally facing away from the Sun.