The Tropic of Capricorn (Southern Tropic)

What is the Tropic of Capricorn?

The Tropic of Capricorn (the Southern Tropic) is the parallel of latitude that delineates the southernmost boundary of Earth's tropical zone. Situated at approximately 23°26'10.7" South latitude (23.4363° S), it defines the exact limit where the Sun can appear at the absolute celestial zenith (90° directly overhead).

For any observer situated south of this line—including all of New Zealand, southern Australia, South Africa's Cape Town, and the southern cone of Argentina and Chile—the midday Sun can never reach the overhead zenith. Even on the longest day of the southern summer, shadows cast on horizontal ground always point toward True South.

Historically designated during antiquity when the Sun was backdropped by the constellation Capricornus during the December solstice, orbital precession has since shifted the astronomical constellation to Sagittarius today.

The December solstice: when the sun is directly overhead

On the December Solstice (occurring annually on December 21 or 22 UTC):

• Maximum Southern Solar Declination: Earth's southern hemisphere reaches its maximum orbital tilt toward the Sun (δ = -ε ≈ -23.44°). The subsolar point strikes the surface perpendicularly along the Tropic of Capricorn.
• Zero Midday Shadows: At exact local solar noon on the solstice, vertical columns, fence posts, and observers on the parallel cast zero shadow.
• Northward Secular Drift: Like the Tropic of Cancer, the Tropic of Capricorn is not stationary. Because Earth's axial obliquity is decreasing by ~0.468 arcseconds per year, the Tropic of Capricorn is migrating northward toward the Equator at roughly 14.4 meters (47.4 feet) per year. Historic markers placed in the 1950s now sit hundreds of meters south of the true astronomical line.

How much of the Tropic of Capricorn is ocean?

While the Northern Tropic passes through massive continental landmasses (North America, North Africa, and the Asian continent), the Southern Tropic is overwhelmingly oceanic:

How long is the Tropic of Capricorn? The calculation

Unlike the Equator (a great circle), the Tropic of Capricorn is a small circle. Computing its true circumference requires calculating the parallel radius r_p on the WGS84 geodetic ellipsoid:

Countries on the Tropic of Capricorn

Explore this curated registry of the 10 sovereign nations traversed by the Tropic of Capricorn, with primary regional locations and celebrated field monuments:

Deserts along the Tropic of Capricorn

Just as the Tropic of Cancer hosts the great northern desert belt, the descending limb of the southern Hadley cell creates hyper-arid conditions across the Tropic of Capricorn:

• The Atacama Desert (Chile): The driest non-polar desert on Earth. Cold oceanic currents (the Humboldt Current) suppress offshore evaporation while the Andes mountain wall blocks Atlantic moisture, leaving parts of the Tropic in the Atacama with zero recorded rainfall across decades.
• The Namib & Kalahari Deserts (Namibia / Botswana): Driven by the cold Benguela Current along southwestern Africa, dense coastal fog blankets shifting dunes along the parallel without producing inland rain.
• The Australian Outback: Spanning the entire width of Australia, the Tropic of Capricorn passes through the Great Sandy Desert, Alice Springs in the Red Centre, and the dry Queensland cattle country before reaching the Pacific coast at Rockhampton.