Tropic of Capricorn

Lore & Background

The Tropic of Capricorn was named when the Sun was in the zodiacal Capricorn at the December (southern) solstice, the date each year when the Sun reaches zenith at this latitude. Due to the precession of the equinoxes, the Sun currently appears in the zodiacal Sagittarius at this solstice. The Tropic of Capricorn is the southern of the two tropics; its Northern Hemisphere counterpart is the Tropic of Cancer.

Reader's Guide

The Tropic of Capricorn serves as the dividing line between the Southern Temperate Zone to the south and the Tropics to the north. The distance between the Arctic Circle and the Tropic of Capricorn remains essentially constant. The Tropic passes through 10 countries, including parts of Africa, Australia, and South America, where it influences climate, agriculture, and ecosystems. In southern Africa, seasonal rainfall supports farming and pasture management, with holistic grazing practices promoted by figures such as Allan Savory. In Australia, areas around the Tropic experience highly variable rainfall, with adaptations in plants and animals, and irrigation from the Great Dividing Range. In South America, the Tropic crosses productive agricultural regions in Brazil and Argentina, while the Andes create the arid Atacama Desert to the west.

Did You Know?

• The Tropic of Capricorn is currently moving northward at a rate of 0.47 arcseconds, or 14.5 meters, per year.
• At solar midnight on the June solstice at the Tropic of Capricorn, the Sun is approximately 43 degrees below the horizon.
• Only four countries are wholly south of the Tropic of Capricorn: Eswatini, Lesotho, Uruguay, and New Zealand.
• The Tropic of Capricorn was named when the Sun was in the zodiacal Capricorn at the December (southern) solstice, but due to precession it now appears in Sagittarius.

Geometric Identity: A Small Circle in the Southern Hemisphere

The Tropic of Capricorn is a circle of latitude sitting at approximately 23°26′09.0″ south of the Equator. Like all parallels, it is an abstract east–west small circle that connects every point on Earth's surface sharing that same latitude coordinate, ignoring elevation. Because it is not the Equator, it is not a great circle; instead it is a smaller ring whose center lies on Earth's rotational axis rather than at Earth's center. Its circumference is shorter than the Equator's, and the length of any parallel can be derived using a cosine function of its latitude. The Tropic is parallel to every other circle of latitude—meaning the planes containing any two of these circles never intersect—and a location's position along it is specified by its longitude. On spherical or ellipsoidal projections, the Tropic, like all parallels except the Equator, qualifies as a rhumb line, and on cylindrical projections such as Mercator or Gall-Peters it runs perpendicular to every meridian.

The December Solstice and the Sun at Zenith

The Tropic of Capricorn holds a unique place in Earth's seasonal cycle. It marks the southernmost latitude on the planet where the Sun can appear directly overhead in the sky, and this occurs specifically at the December solstice. This property is shared with its northern counterpart, the Tropic of Cancer, which serves the same role for the June solstice. The latitude of both tropical circles is numerically equal to the Earth's axial tilt—the angle between the planet's rotational axis and the perpendicular to its orbital plane. If the Earth's axis were perfectly upright, with no tilt relative to its orbital plane, the Sun would always rise due east, pass directly overhead at the equator, and set due west, and neither the Tropic of Capricorn nor the Tropic of Cancer would exist. The Tropic, together with the Equator and the two polar circles, delineates the five principal geographical zones that divide the planet's surface into distinct climatic and astronomical regions.

A Slowly Migrating Boundary: The Shifting Axial Tilt

Perhaps the most fascinating aspect of the Tropic of Capricorn is that it is not, in any strict sense, a fixed line. Its latitude depends entirely on the obliquity of the ecliptic—the tilt of Earth's axis relative to the plane of its orbit around the Sun—and that tilt is in constant, slow flux. These changes, though imperceptible in a human lifetime, mean that the Tropic of Capricorn is a slowly migrating boundary whose position will shift noticeably over tens of thousands of years.

Cartographic Representation and Political Borders

How the Tropic of Capricorn appears on a flat map depends entirely on the projection chosen. On an equirectangular projection centered on the equator, it renders as a straight horizontal line, parallel and equally spaced from its neighbors. On a Mercator projection, parallels near the poles are stretched wider to preserve local shapes and scales, so the Tropic sits in a region where spacing is still relatively moderate. On a Gall-Peters projection, the spacing near the poles is compressed to keep area comparisons accurate, altering the Tropic's visual position relative to other features. On non-cylindrical and non-pseudocylindrical projections, the Tropic need not be straight or parallel to other parallels at all. Beyond cartography, circles of latitude carry practical geopolitical significance. Where natural borders are absent—deserts, open ocean—governments and treaties often draw boundaries along a parallel. North American examples include Colorado's northern edge at 41° N and southern edge at 37° N, and roughly half the United States–Canada border tracing 49° N.