The Tropic of Capricorn is an imaginary line of latitude going around the Earth at approximately 23.5° south of the equator. It is the southernmost point on Earth where the sun's rays can be directly overhead at local noon. It is also one of the five major circles of latitude dividing the Earth (the others are the Tropic of Cancer in the northern hemisphere, the equator, the Arctic Circle and the Antarctic Circle).
Geography of the Tropic of Capricorn
The Tropic of Capricorn is significant to understanding the Earth's geography because it marks the southern boundary of tropics. This is the region that extends from the equator south to the Tropic of Capricorn and north to the Tropic of Cancer.
Unlike the Tropic of Cancer, which passes through many areas of land in the northern hemisphere, the Tropic of Capricorn passes mainly through water because there is less land for it to cross in the southern hemisphere. However, it does cross through or is near places like Rio de Janeiro in Brazil, Madagascar, and Australia.
Naming of the Tropic of Capricorn
Around 2,000 years ago, the sun crossed into the constellation of Capricorn at the winter solstice around December 21. This resulted in this line of latitude being named the Tropic of Capricorn. The name Capricorn itself comes from the Latin word caper, meaning goat and was the name given to the constellation. This was then later transferred to the Tropic of Capricorn. It should be noted, however, that because it was named over 2,000 years ago, the specific location of the Tropic of Capricorn today is no longer in the constellation Capricorn. Instead, it is located in the constellation Sagittarius.
Significance of the Tropic of Capricorn
In addition to being used to aid in dividing the Earth into different parts and marking the southern boundary of the tropics, the Tropic of Capricorn, like the Tropic of Cancer is also significant to the Earth's amount of solar insolation and the creation of seasons.
Solar insolation is the amount of Earth's direct exposure to the sun's rays from incoming solar radiation. It varies over the Earth's surface based on the amount of direct sunlight hitting the surface and it is mostly when it is directly overhead at the subsolar point which migrates annually between the Tropics of Capricorn and Cancer based on the Earth's axial tilt. When the subsolar point is at the Tropic of Capricorn, it is during the December or winter solstice and is when the southern hemisphere receives the most solar insolation. Thus, it is also when the southern hemisphere's summer begins. Furthermore, this is also when the areas at latitudes higher than the Antarctic Circle receive 24 hours of daylight because there is more solar radiation to be deflected south due to the Earth's axial tilt.