Tropic of Cancer
Northernmost latitude where the Sun appears directly overhead.
The Tropic of Cancer is the Earth's northernmost circle of latitude where the Sun can be seen directly overhead, occurring on the June solstice. It is one of the seven major circles of latitude and marks the northern boundary of the tropics, with its position determined by the tilt of Earth's axis. The line is named for the zodiacal constellation Cancer, which the Sun occupied at the June solstice when the name was given in the last centuries BC.
- Daylight at summer solstice
- 13 hours, 35 minutes
- Daylight at winter solstice
- 10 hours, 41 minutes
- Countries crossed
- 17 (including two disputed territories)
- Highest mountain on or adjacent
- Yu Shan in Taiwan
Lore & Background
Geographically, the Tropic of Cancer passes through 17 countries and 8 water bodies. North of it lie the subtropics and the North Temperate Zone. The climate along the tropic is generally hot and dry, except for cooler highland regions and easterly coastal areas with heavy orographic rainfall. Much land on or near the Tropic is part of the Sahara Desert. In geopolitics, the Tropic of Cancer serves as the southern limitation for the mutual defence obligation of NATO; member states are not obligated to defend territory south of this line. For aviation, the Fédération Aéronautique Internationale requires a round-the-world speed record flight to cover a distance no less than the length of the Tropic of Cancer and cross all meridians.
Reader's Guide
The Tropic of Cancer is a fundamental reference line in geography, astronomy, and geopolitics. Astronomically, it marks the northernmost latitude where the Sun can be directly overhead, a phenomenon tied to Earth's axial tilt and the June solstice. Its drifting position—currently moving southward by about 15 meters per year—illustrates the dynamic nature of Earth's orientation in space, influenced by axial precession and long-term tilt variations. This drift has practical implications for mapping and navigation, as the line's exact location must be updated continuously. Geographically, the Tropic of Cancer defines the northern boundary of the tropics, a region that contains diverse climates from the Sahara Desert to monsoonal areas. The line also appears in international law, notably as the southern limit of NATO's mutual defence commitment, affecting strategic planning. Culturally and historically, the name 'Tropic of Cancer' reflects ancient astronomical observations, though precession has since shifted the Sun's position at the solstice from Cancer to Taurus. Overall, the Tropic of Cancer remains a key marker of Earth's geometry, climate zones, and human systems.
Did You Know?
- The highest mountain on or adjacent to the Tropic of Cancer is Yu Shan in Taiwan.
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