The world is divided into five latitudinal thermal zones. The following are the thermal zones:

A. Torrid Zone:

1. It is the largest zone of the thermal zones.

2. It covers almost half of the area of the earth's surface.

3. It is situated between the Tropic of Cancer and Tropic of Capricorn.

4. The sun's rays are almost vertical throughout the year in this zone.

5. The mid day sun is overhead at equator on equinoxes i.e. on 21st March and 23rd September.

6. It is also overhead at Tropic of Cancer on 21st June and at Tropic of Capricorn on 22nd December.

B. Temperate Zone:

1. The temperate zones are on either side of the torrid zone.

2. The North Temperate zone lies between Tropic of Cancer (23 1/2° N) and Arctic Circle (661/2°).

3. The South temperate zone lies between the Tropic of Capricorn (23 1/2°S) and Antarctic Circle (661/2°S).

4. The sun is never overhead in this zone in the winter season. The nights are longer and days are shorter and vice-versa in summer.

5. The difference between the duration of day in summer and that of night in winter in the polar circles is 24 hours.

C. Frigid Zone:

1. The frigid zone is found in both hemispheres like the temperate zone.

2. The North Frigid zone lies between the Arctic Circle (66 1/2°N) and the North Pole (90°N).

3. The South Frigid Zone lies between the Antarctic Circle (66 1/2°S) and South Pole (90°S).

4. During the winter season the sun does not rise above the horizon for almost six months.

5. These are the coldest regions of the world.