Incoming solar radiation that reaches the earth and atmosphere is called insolation, which consists of visible and ultraviolet light.
A climate zone is characterized by weather events that occur predictably for at least 30 years. Insolation is one factor that influences climate. The tropical climate zone is one of five major climate zones that extend from the Tropic of Cancer at 23.5 degrees north latitude to the Tropic of Capricorn at 23.5 degrees south latitude.
Imaginary horizontal lines on a map stretch east and west from 90 degrees north latitude at the North Pole to -90 degrees latitude at the South Pole.
Sunlight is more intense when it is directly overhead and strikes the earth perpendicularly rather than at a slanted angle. Direct sunlight occurs most consistently in latitudes close to the equator.
The earth is tilted 23.5 degrees relative to its elliptical orbit around the sun. The earth is always pointing in the same direction in space. Therefore, when the northern hemisphere is tipped toward the sun, summer occurs, along with longer days and generally warmer weather. At the same time winter occurs in the southern hemisphere. The tropical climate zone, at and around the equator, is tipped toward the sun all year long, 12 hours a day, so this region always experiences summer-like weather and receives the highest insolation.