Cause of the Seasons

Earth's Seasons Are Caused by the Axial Tilt! No Tilt, No Seasons.

Solstices: Locations in Earth's orbit when the axis is pointed the most toward or away from the Sun. The longest and shortest day of the year depending on which hemisphere you live, North or South.

Equinoxes: Locations in Earth's orbit when the axis is not pointed at all toward or away from the Sun, but tangent to it. Length of the day is the same for everyone on Earth. 12 hours of day and 12 hours of night.

Earth's rotation axis Precesses about in a 26,000 year cycle. This Changes the Date of Equinoxes and Solstices. 

Seasons happen because sunlight is distributed over the surface of Earth differently throughout the year, NOT because the Earth is closer or farther away.
When Sunlight is direct is delivers more energy per unit surface area than when it is indirect (or oblique).
Tilt also causes length of days to change. During summer, days are longer and sunlight is more direct. During winter, days are short and sunlight is more oblique.