Capricorn marks December’s farthest overhead sun
The Tropic of Capricorn holds the subsolar point at the December solstice—the southernmost latitude where the Sun stands straight overhead. North of it lie the tropics; south begins the Southern Temperate Zone. Cancer is its northern twin.
At the moment this circle was named, the December solstice sun stood in the zodiac sign of the Goat; because the equinoxes precess, that sun now appears in Sagittarius. On the June solstice the relationship flips, and at solar midnight the sun lies 90 degrees beneath the horizon all around. The line is one of five major circles drawn on world maps and sits at about 23.436 degrees south, a figure that keeps changing.
That change comes from the wobble in Earth's tilt, which ranges from about 22.1 to 24.5 degrees over 41,000 years. The circle is edging north at nearly half an arcsecond a year, roughly 15 meters, having been at 23°27′S in 1917 and due at 23°26′S in 2045, so its distance from the Arctic Circle hardly varies. Along it, daylight runs from about 10 hours 41 minutes in the southern winter to 13 hours 35 minutes in summer, and the full loop measures about 36,788 kilometers across 10 countries.
Land along the southern line varies sharply. In southern Africa rain is usually dependable enough for farming, and short, rotational grazing, promoted by the Zimbabwean-born biologist Allan Savory, helps hold soil against erosion. Near the line Australia has some of the most erratic rainfall anywhere; beyond the Great Dividing Range lie the Channel Country's intermittent rivers, Kati Thanda-Lake Eyre and the Gibson Desert. In Brazil humid Atlantic air feeds rich sugarcane country, where the original Atlantic Forest survives only in patches, while west of the Andes the cold Humboldt Current helps make the Atacama one of the driest deserts on Earth.
Because most land lies in the north, only four countries sit entirely south of this line, compared with 73 wholly north of its northern twin.
Source: Tropic of Capricorn
