On June 21st of every year, the southern hemisphere begins the season of, and the northern hemisphere begins the season of.

On June 21 of each year, the southern hemisphere begins the winter season and the northern hemisphere begins the summer season.

Explanation:

We call season each of the four subdivisions of the year based on weather patterns. They are: spring, summer, autumn and winter.

The seasons of the year are due to the slope of the earth in relation to the sun. We can then say that the seasons are caused by the Earth's axis of rotation, along with its movement around the sun, which lasts one year and is called a translation.

On June 21st of every year, the southern hemisphere begins the season of winter, and the northern hemisphere begins the season of summer.