Summer is the hottest of the four temperate seasons, falling between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, with day-length decreasing as the season progresses after the solstice. The date of the beginning of summer varies according to climate, tradition and culture, but when it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, and vice versa. Schools and universities typically have a summer break to take advantage of the warmer weather and longer days. In almost all countries, children are out of school during this time of year for summer break, although dates vary. In the United States, public schools usually end in early June. People take advantage of the warmer temperatures by spending more time outdoors during the summer. Activities such as traveling to the beach and picnics occur during summer months. Sports such as basketball, American football, volleyball, skateboarding, baseball, softball, cricket, tennis, golf and water polo are played. Water sports, such as water skiing, wake boarding, swimming, surfing, and tubing are also enjoyed.