Tropics and Climate Zones
If we go 23 1/2 north of the Equator we encounter a special dashed parallel called the Tropic of Cancer; if we go the same distance south we see its companion the Tropic of Capricorn. The former is at the latitude at which the Sun passes directly overhead on the first day of summer in the Northern Hemisphere, while the latter is where the Sun passes overhead on the first day of Southern Hemisphere summer (or Northern Hemisphere Winter); these evens occur, respectively, about June 22nd and December 22nd.
The portion of the Earth between the two "tropics" is called the Torrid Zone - the region of perpetual summer. Also, within the Torrid Zone, and nowhere else on Earth, the Sun appears overhead at least once per year; at these circles it does occur once, but at locations between them the Sun passes overhead twice each year.
Look now 23 1/2 from the North Pole and you'll see another dashed parallel labeled the Arctic Circle, and the same distance from the South Pole we have its southern companion, the Antarctic Circle. The area between these circles and the poles constitute the Frigid Zones, or we might say the region of perpetual winter. Between the Arctic Circle and the Tropic of Cancer is the North Temperate Zone, and its southern companion, the South Temperate Zone lies between the Tropic of Capricorn and the Antarctic Circle. These Zones, which are each larger than the previously mentioned ones are -- as their name implies -- where the climate is temperate and where most of the Earth's people prefer to live. Here is also where we have the yearly cycle of four seasons, except that a particular season occurs a half-year apart in the Northern and Southern Temperate Zones because of the 23 1/2 tilt of our Earth as it travels it's orbit around the Sun.
The Frigid Zones are also "The Land of the Midnight Sun" because in this area the Sun never sets during some portion of the year: a day or so along the Arctic and Antarctic Circles, and an entire six months at the poles. Between these circles and the poles, the period in which the Sun does not set varies according the latitude; the closer to the pole we go the longer it is. Similarly, there is a corresponding period each year when the Sun doesn't rise in the Frigid Zones, and this period again increases as we go closer to the poles.