The following are the thermal zones.
 Torrid Zone
It is the largest of the thermal zones.
It covers almost half the area of the earth’s surface.
It is situated between the Tropic of Cancer (23½°N) and Tropic of Capricorn (23½0 South).
The sun’s rays are almost vertical throughout the year in this zone.
The mid-day sun is overhead at the equator on equinoxes, i.e. on 21st March and 23rd September.
It is also overhead at Tropic of Cancer on 21st June and at Tropic of Capricorn on 22nd December.
The duration of day and night are always equal i.e. 12 hours each on the equator and they increase to 13 hours 27 minutes at tropics.
The range of temperature is lowest at the equator and it increases towards the tropics.
 Temperate Zone
The temperate zones are on either side of the Torrid zone.
The North Temperate Zone lies between Tropic of Cancer (23½0 North) and Arctic Circle (66½o North).
The South Temperate Zone lies between Tropic of Capricorn (23½° South) and Antarctic Circle (66½° South).
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.
The difference between the duration of the day and night increases towards the poles.
The maximum duration of the day in summer and that of the night in winter in the polar circles is 24 hours.
When it is summer in the northern hemisphere it is winter in the southern hemisphere and vice versa.
 Frigid Zones
Like the temperate zone, Frigid Zone is also found in both the hemispheres.
The North Frigid Zone lies between Arctic Circle (66½0N) and North Pole (90° North).
The South Frigid Zone lies between Antarctic Circle (66½0 South) and South Pole (900 South).
During the winter season, the sun does not rise above the horizon for almost six months.
These are the coldest regions of the world.
The surface remains permanently frozen under thick snow.