The Tropic of Cancer and the Tropic of Capricorn are the northern and southern lines of latitude, respectively, that are the bounds for the tropics. The equator lies midway between these two lines. The word “tropic” comes from a Greek term “tropos,” which means “turn” or “change.” This refers to the fact that the Sun appears to “turn back” when it reaches these latitudes. The Tropic of Cancer is the northernmost latitude where the Sun is ever directly overhead, which occurs on the June solstice. Meanwhile, the Tropic of Capricorn is the southernmost latitude where the Sun can be overhead, which happens on the December solstice.
Do The Tropic of Cancer and Capricorn Change?
Presently, the Tropic of Cancer is 23°26′10.5″ (or 23.43624°) N, while the Tropic of Capricorn is 23°26′10.5″ (or 23.43624°) S. While their positions are always the same values as each other (equidistant from the equator), they constantly change because the Earth’s axial tilt varies from 22.1 degrees to 24.5 degrees. Right now, the Tropic of Cancer is moving south and the Tropic of Capricorn is moving north at the rate of about 15 meters per year.
The Tropic of Cancer
Definition and Range
The Tropic of Cancer is an imaginary line of latitude that is approximately 23.5 degrees north of the Equator. It marks the northernmost point on Earth where the Sun is directly overhead at noon. This happens once a year, at the June solstice, around the 21st of the month.
Name Origin
The Tropic of Cancer got its name because, when it was named about 2,000 years ago, the Sun was in the direction of the constellation Cancer (Latin for crab) at the June solstice. Due to the precession of the equinoxes, this is no longer the case. Currently, the Sun is in the direction of the constellation Taurus during the June solstice. The Sun reappears in the constellation Cancer approximately every 24,000 years.
Geography and Climate
The Tropic of Cancer passes through 16 countries, including Mexico, Egypt, India, and China, among others. It also crosses the Atlantic, Pacific, and Indian Oceans. Regions lying along the Tropic of Cancer generally experience a tropical desert or tropical savanna climate. In these areas, average high temperatures are consistently above 18 °C (64 °F) throughout the year, and rainfall varies from quite abundant to very scarce.
The Tropic of Capricorn
Definition and Range
The Tropic of Capricorn, on the other hand, is an imaginary line of latitude located approximately 23.5 degrees south of the Equator. It signifies the southernmost position where the Sun is directly overhead at noon. This event takes place once a year, during the December solstice, around the 21st of the month.
Name Origin
Like its northern counterpart, the Tropic of Capricorn was named approximately 2,000 years ago when the sun was in the direction of the constellation Capricornus (Latin for goat horn) at the December solstice. Today, due to the precession of the equinoxes, the Sun is in the direction of the constellation Sagittarius during the December solstice.
Geography and Climate
The Tropic of Capricorn crosses through ten countries, including Australia, Brazil, and South Africa, and spans the Atlantic, Pacific, and Indian Oceans. The climates along the Tropic of Capricorn are similar to those along the Tropic of Cancer, mostly characterized by tropical desert and savanna climates, although this can vary depending on regional geography and prevailing weather patterns.
Historical and Present Day Importance
Historically, the Tropics of Cancer and Capricorn have held astronomical importance, helping ancient people understand the Sun’s yearly path across the sky and serving as a geographical framework for celestial navigation. This understanding facilitated migration, trade, and the spread of cultures and ideas.
Today, they continue to hold importance in terms of climate and seasonal weather. These tropic lines help demarcate different climate zones on Earth, which are critical for weather forecasting and climate study. The regions lying between these two lines of latitude, known as the tropics, have a unique climate that has little seasonal variation in temperature, high humidity, and substantial rainfall. These conditions make the tropics the most biodiverse places on Earth, home to numerous plant and animal species.
Moreover, the positioning of the tropics is vital for the global energy balance. The Sun’s rays are most direct in these regions, and they absorb more solar energy than they reflect back to space. This helps drive global atmospheric circulation and weather patterns.
In the context of climate change, the tropics are significant as they’re vulnerable to changes in temperature and precipitation patterns. Therefore, understanding the climatic nuances of these regions is crucial in developing climate models and planning for future climate change impacts.
References
- Bakker G., et al. (1995). Radio Positioning at Sea: Geodetic Survey Computations Least Squares Adjustment. ISBN 90-6275-537-2.
- Hohenkerk, C.Y., Yallop, B.D., Smith, C.A., & Sinclair, A.T. “Celestial Reference Systems” in Seidelmann, P.K. (ed.) Explanatory Supplement to the Astronomical Almanac. Sausalito: University Science Books.
- Keay, R.W.J. (1959). Vegetation map of Africa south of the Tropic of Cancer. Explanatory notes. Oxford University Press.
- Lerner, K. Lee; Lerner, Brenda Wilmoth (2003). World of Earth Science. Farmington Hills, MI: Thomson-Gale. ISBN 0-7876-9332-4.