The Tropics are centered on the equator and limited in latitude by the Tropic of Cancer in the northern hemisphere, at approximately 23°26' (23.4°) N latitude, and the Tropic of Capricorn in the southern hemisphere at 23°26' (23.4°) S latitude. This region is also referred to as the tropical zone and the torrid zone (see geographical zone).

On the other hand, in the temperate zones, north of the Tropic of Cancer and south of the Tropic of Capricorn, the sun never reaches the zenith, always passing south of it in the northern hemisphere, and north of it in the southern.

The word "tropics" comes from Greek tropos meaning "turn" or "direction", because the apparent position of the Sun oscillates between the two tropics with a period that defines the average length of a year.

Tropical seasons and climate

main: Tropical climate The seasons in the tropics are dominated by the movement of the tropical rain belt (or ITCZ), which oscillates from the northern to the southern tropics over the course of the year, thus causing the dry season and the wet season in turn.

The seasons (autumn, winter, spring, and summer) are caused by the Earth's tilt. Direct rays of the sun always shine in and between the tropics. When it's the first day of winter in the Northern Hemisphere, the direct rays are over the Tropic of Capricorn, which is called the winter solstice. There are the shortest hours of daylight. When it's the first day of summer in the Northern Hemisphere, the direct rays are over the Tropic of Cancer, known as the summer solstice. There are the longest hours of daylight. When it's either the first day of spring or autumn in the Northern Hemisphere, it is known as an equinox. The word comes from another word meaning "equal night." The direct rays are over the equator, meaning 12 hours of day and night for everyone all over the world. Equinoxes occur two days out of the whole year.

Tropical is sometimes used in a general sense for a tropical climate that is warm to hot and moist year-round, often with the sense of lush vegetation. However, there are places in the tropics that are anything but "tropical" in this sense, with even alpine tundra and snow-capped peaks, including Mauna Kea, Mt. Kilimanjaro, and the Andes as far south as the northernmost parts of Chile and Argentina. There are also places in the tropics which are desert, with extreme heat, such as the Sahara Desert and Australian Outback.

Tropical ecosystems

In biogeography, the tropics are divided into paleotropics (Africa, Asia and Australia) and neotropics (Central and South America). Together, they are sometimes referred to as the pantropics. The neotropic region should not be confused with the ecozone of the same name; in the Old World, this is unambiguous as the paleotropics correspond to the Afrotropical, Indomalayan, and partly the Australasian and Oceanic ecozones.