World map showing the Tropic of CapricornRelationship of Earth's axial tilt (ε) to the tropical and polar circles
TheTropic of Capricorn (or theSouthern Tropic) is thecircle of latitude that contains thesubsolar point at the December (or southern)solstice. It is thus the southernmost latitude where the Sun can be seen directly overhead. It also reaches 90 degrees below the horizon at solar midnight on theJune Solstice. Its northern equivalent is theTropic of Cancer.
The Tropic of Capricorn is one of the five major circles of latitude marked on maps ofEarth. Its latitude is currently 23°26′09.6″ (or 23.43599°)[1] south of theEquator, but it is very gradually moving northward, currently at the rate of 0.47arcseconds, or 15 metres, per year.
The Tropic of Capricorn's position is not fixed, but constantly changes because of a slight wobble in the Earth's longitudinal alignment relative to its orbit around the Sun. Earth'saxial tilt varies over a 41,000 year period from about 22.1 to 24.5 degrees and currently resides at about 23.4 degrees. This wobble means that the Tropic of Capricorn is currently drifting northward at a rate of almost half an arcsecond (0.468″) of latitude, or 15 metres, per year (it was at exactly 23° 27′S in 1917 and will be at 23° 26'S in 2045). Therefore, the distance betweenArctic Circle and the Tropic of Capricorn is essentially constant moving in tandem. See undercircles of latitude for information.
There are approximately 10 hours, 41 minutes of daylight during the June solstice (Southern Hemisphere winter). During the December solstice (Southern Hemisphere summer), there are 13 hours, 35 minutes of daylight. The length of the Tropic of Capricorn at 23°26′11.7″S is 36,788 km (22,859 mi).[3]
In most of this belt ofsouthern Africa, a minimum of seasonal rainfall is reliable and farming is possible, though yields struggle to compete with for example theMississippi basin, even against like-to-like soilfertilisers. Rivers have been successfully dammed particularly flowing fromrelief precipitation areas (high eminences) and those from the edge of theGreat Rift Valley, such as theZambezi, well within the Tropics. This, with alluvial or enriched soil, enables substantial yield grain farming in areas with good soil. Across this large region pasture farming is widespread, where intensive, brief and rotational it helps to fertilise and stabilise the soil, preventing run-off anddesertification.[4] This approach is traditional to many tribes and promoted by government advisors such asAllan Savory, a Zimbabwean-born biologist, farmer, game rancher, politician and international consultant and co-founder of theSavory Institute. According to theUnited Nations University Our World dissemination he is credited with developing "holistic management" in the 1960s and has led anti-desertification efforts in Africa for decades using a counterintuitive approach to most developed economies of increasing the number of livestock on grasslands rather than fencing them off for conservation. Such practices in this area have seen success and won generous awards; he gave the keynote speech at UNCCD's Land Day in 2018, and later that year aTED (conference) address, widely re-broadcast.[4]
A sign marking the Tropic of Capricorn as it passes throughNamibia
A monument marking the Tropic of Capricorn as it passes throughBotswana
InAustralia, areas around the Tropic have some of the world's most variablerainfall.[5] In the east advanced plants such as flowering shrubs andeucalyptus and in most bioregions grasses have adapted to cope with means such as deep roots and littletranspiration. Wetter areas, seasonally watered, are widely pasture farmed. As to animals, birds andmarsupials are well-adapted. Naturally difficultarable agriculture specialises in dry fruits, nuts and modest water consumption produce. Other types are possible given reliable irrigation sources and, ideally, water-retentive enriched oralluvial soils, especially wheat; shallow irrigation sources very widely dry up in and afterdrought years. The multi-ridgeGreat Dividing Range bringsrelief precipitation enough to make hundreds of kilometres either side cultivable, and its rivers are widely dammed to store necessary water; this benefits the settled areas ofNew South Wales andQueensland.
Behind the end of the green hills, away from thePacific, which is subject to warm, negative phases of theEl Niño–Southern Oscillation (colloquially this is an "El Niño year/season") is a white, red and yellow landscape of 2,800 to 3,300 kilometres ofrain shadow heading west in turn feature normally arid cattle lands of theChannel Country, the whiteKati Thanda-Lake Eyre National Park, the mainly redMamungari Conservation Park, then theGibson Desert, after others the dry landscape settlement ofKalbarri on the west coast and its rest, northward. TheChannel Country features an arid landscape with a series of ancientflood plains from rivers which only flow intermittently. The principal rivers areGeorgina River,Cooper Creek and theDiamantina River. In most years, their waters are absorbed into the earth or evaporate, but when there is sufficient rainfall in their catchment area, these rivers flow intoLake Eyre, South Australia. One of the most significant rainfall events occurred in 2010 when a monsoonal low from ex-Cyclone Olga created a period of exceptional rainfall.[6]
El Niño adverse phases cause a shift in atmospheric circulation; rainfall becomes reduced over Indonesia and Australia, rainfall and tropical cyclone formation increases over the tropical Pacific.[7] The low-level surfacetrade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction.[7]
Spire marking Tropic of Capricorn inRockhampton,Queensland (4 km north of the actual Tropic of Capricorn)
Monument marking Tropic of Capricorn near Civic Centre, Longreach, at mid-day ofSummer solstice 2019. The monument is few arc seconds south of the Tropic of Capricorn (notice the shadow directly below the sign)
InSouth America, whilst in the continentalcratons soils are almost as old as in Australia and Southern Africa, the presence of the geologically young and evolvingAndes means that this region is on the western side of the subtropicalanticyclones and thus receives warm and humid air from theAtlantic Ocean. As a result, areas inBrazil adjacent to the Tropic are impressively productive agricultural regions, producing large quantities of crops such assugarcane, and the naturalrainforest vegetation has been almost entirely cleared, except for a few remaining patches ofAtlantic Forest. Further south inArgentina, the temperate grasslands of thePampas region is equally influential inwheat,soybeans,maize, andbeef, making the country one of the largest worldwide agricultural exporters, similar to the role played by thePrairies region inCanada.
As most of Earth's land is in theNorthern Hemisphere only four countries are wholly south of the Tropic of Capricorn (which contrasts with 73, about one third of the current total, wholly north of theTropic of Cancer):
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