Solstice is the time of year that the sun is farthest from the equator, north or south.
It's the longest day of the year in the northern hemisphere and the shortest day in the southern hemisphere. Seasons are caused by the angle of the earth on its axis. In summer, the sun is highest in the sky, so the sun's rays are concentrated making it hot. With the summer solstice comes the Strawberry Moon, the Full moon in June. Summer solstice does not always fall on June 21st, it just seems that way.