Tropic of Cancer
The northernmost circle where the Sun stands directly overhead.
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The Tropic of Cancer is the Earth's northernmost circle of latitude at which the Sun can appear directly overhead, an event that occurs on the June solstice when the Northern Hemisphere reaches its maximum tilt toward the Sun. It is the northern counterpart of the Tropic of Capricorn, and together with the Arctic and Antarctic circles, the Equator, and the Poles, these form the seven major circles of latitude.
The position of the Tropic of Cancer is determined by the tilt of Earth’s axis, which varies over a 41,000-year cycle between roughly 22.1 and 24.5 degrees; currently, the tilt is about 23.4 degrees. Because of this axial wobble and precession, the Tropic of Cancer is not fixed but drifts southward by nearly half an arcsecond (about 15 meters) per year. Its location was exactly 23°27′N in 1917 and will reach 23°26′N in 2045.
Name
The name originates from the last centuries BC, when the Sun was in the zodiacal constellation Cancer (the Crab) at the June solstice; due to the precession of the equinoxes, the Sun now appears in Taurus during that solstice. The term "tropic" comes from the Greek "tropē," meaning a turn or change, referencing the Sun’s apparent reversal of direction at the solstices. Geopolitically, the Tropic of Cancer marks the southern limit for mutual defense obligations under NATO; member states are not required to defend territory south of this line.
Climate
The climate along the Tropic is generally hot and dry, except in cooler highlands in China, marine areas like Hawaii, and eastern coasts where orographic rainfall can exceed 4 meters annually. Most regions experience two seasons: an extremely hot summer with temperatures often reaching 45°C and a warm winter with highs around 22°C. Much of the land on or near the Tropic is part of the Sahara Desert, while eastern areas have a torrid monsoonal climate with a short wet season from June to September. The highest mountain on or adjacent to the Tropic is Yu Shan in Taiwan, which had glaciers descending to 2,800 meters during the Last Glacial Maximum; the nearest surviving glaciers are the Minyong and Baishui in the Himalayas to the north and on Pico de Orizaba in Mexico to the south. The length of the Tropic of Cancer is 36,788 kilometers, and it is used as a minimum distance requirement for round-the-world speed records under Fédération Aéronautique Internationale rules.
Lore & Background
When this line of latitude was named in the last centuries BC, the Sun was in the zodiacal Cancer at the June solstice. Due to the precession of the equinoxes, this is no longer the case; today the Sun is in the zodiacal Taurus at the June solstice. The word 'tropic' itself comes from the Greek 'tropē', meaning turn or inclination, referring to the fact that the Sun appears to 'turn back' at the solstices. The Tropic of Cancer's position is not fixed, but constantly changes because of axial precession.
Earth's axial tilt varies over a 41,000-year period from about 22.1 to 24.5 degrees, and is about 23.4 degrees. This wobble means that the Tropic of Cancer is currently drifting southward at a rate of almost half an arcsecond (0.468″) of latitude, or 15 m, per year. The circle's position was at exactly 23°27′N in 1917 and will be at 23°26'N in 2045.
Reader's Guide
North of the tropic are the subtropics and the North Temperate Zone. The equivalent line of latitude south of the Equator is called the Tropic of Capricorn, and the region between the two, centered on the Equator, is the tropics. In the year 2000, more than half of the world's population lived north of the Tropic of Cancer. On the Tropic of Cancer there are approximately 13 hours, 35 minutes of daylight during the summer solstice.
During the winter solstice, there are 10 hours, 41 minutes of daylight. Using 23°26'N for the Tropic of Cancer, the tropic passes through 17 countries (including two disputed territories) and 8 water bodies, starting at the prime meridian and heading eastward. The climate at the Tropic of Cancer is generally hot and dry, except for cooler highland regions in China, marine environments such as Hawaii, and easterly coastal areas, where orographic rainfall can be very heavy. Most regions on the Tropic of Cancer experience two distinct seasons: an extremely hot summer with temperatures often reaching 45°C and a warm winter with maxima around 22°C. Much land on or near the Tropic of Cancer is part of the Sahara Desert, while to the east, the climate is torrid monsoonal with a short wet season from June to September.
The highest mountain on or adjacent to the Tropic of Cancer is Yu Shan in Taiwan. It had glaciers descending as low as 2800 m during the Last Glacial Maximum. At present glaciers still exist around the Tropic. The nearest currently surviving are the Minyong and Baishui in the Himalayas to the north and on Pico de Orizaba in Mexico to the south.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Tropic of Cancer (CC BY-SA 4.0).
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