QUICK FACTS
Created Jan 0001
Status Verified Sarcastic
Type Existential Dread
Keywords
june solstice, northern hemisphere, december solstice, equator, southern hemisphere, tropic of capricorn, arctic, antarctic

Tropic Of Cancer

“The Tropic of Cancer, also known rather uninterestingly as the Northern Tropic, is the absolute northernmost line of latitude on our planet where the Sun can...”

Contents
  • 1. Overview
  • 2. Etymology
  • 3. Cultural Impact

The Tropic of Cancer, also known rather uninterestingly as the Northern Tropic, is the absolute northernmost line of latitude on our planet where the Sun can manage to be directly overhead. This celestial alignment happens precisely on the June solstice , a day when the Northern Hemisphere is practically bowing down to the Sun, tilted towards it with every ounce of its being. It’s also the day that marks the longest period of daylight for those of us unfortunate enough to reside in the Northern Hemisphere. On the flip side, during the December solstice , this same line of latitude experiences the Sun at its lowest point in the sky, reaching a full 90 degrees below the horizon at solar midnight.

The exact position of this line isn’t etched in stone, you see. It’s a dynamic measurement, currently calculated at approximately 23°26′09.3″ north of the Equator . This number, 23.43591 degrees for the numerically inclined, shifts ever so slightly over time. Its counterpart in the Southern Hemisphere , which marks the Sun’s most southerly zenith, is the Tropic of Capricorn . These two tropics, along with the Arctic and Antarctic circles, the Equator , and the degenerate circles that are the Poles , form the seven primary circles of latitude that grace our maps. The position of the Tropic of Cancer, relative to the Equator, is dictated by the planet’s axial tilt – that cosmic wobble as we spin on our axis relative to our orbital plane. As this tilt changes, so too does the latitude of these tropics.

From a strictly geopolitical standpoint, the Tropic of Cancer holds a peculiar significance. It serves as the southern boundary for the mutual defense obligation of NATO . In simpler terms, if trouble brews south of this line, NATO member states aren’t automatically bound to rush to each other’s aid. It’s a rather arbitrary line on a map with very real consequences.

Name

When this particular line of latitude was christened, likely in the last few centuries BC, the Sun, during the June solstice , was positioned in the constellation Cancer – the Crab, if you prefer your Latin. The word “tropic” itself whispers of Greek origins, from “trope” (τροπή), meaning a turn or an inclination. It aptly describes how the Sun, from our perspective, appears to “turn back” at the solstices, reversing its apparent northward or southward journey across the sky. However, thanks to the slow, inexorable creep of axial precession , the Sun no longer graces the constellation Cancer at the June solstice. Today, it’s more likely to be found lounging in Taurus . The celestial cartography has shifted, but the name, like a stubborn old landmark, remains.

Drift

The Tropic of Cancer is not a static entity. It’s a line in constant, albeit slow, motion. This drift is a direct consequence of axial precession , a phenomenon affecting the Earth’s longitudinal orientation relative to the ecliptic – the plane of our orbit around the Sun. The Earth’s axial tilt itself isn’t constant; it oscillates over a cycle of about 41,000 years, varying between roughly 22.1 and 24.5 degrees. As of the year 2000, the tilt was around 23.4 degrees, a figure expected to hold for roughly another millennium. This subtle wobble means the Tropic of Cancer is currently migrating southward, inching along at a glacial pace of nearly half an arcsecond per year, which translates to about 15 meters. Back in 1917, it was positioned at precisely 23°27′N, and it’s projected to be at 23°26′N by 2045.

Interestingly, the distance between the Tropic of Cancer and its southern counterpart, the Antarctic Circle , remains relatively constant because they move in tandem. This assumes, of course, that the equator itself remains fixed, which is a simplification. The precise location of the equator is also subject to subtle variations. For a deeper dive into the mechanics of this celestial dance, one might consult the articles on Equator , axial tilt , and circles of latitude .

Geography

To the north of the Tropic of Cancer lie the subtropics and the vast expanse of the North Temperate Zone . The region situated between the Tropic of Cancer and the Tropic of Capricorn, encompassing the Equator, is known as the tropics . As of the year 2000, a rather significant portion of humanity, over half the global population, resided north of the Tropic of Cancer.

On the Tropic of Cancer itself, the amount of daylight varies considerably between the seasons. During the summer solstice, one can expect approximately 13 hours and 35 minutes of daylight. Conversely, the winter solstice offers a considerably shorter day, with around 10 hours and 41 minutes of sunlight.

Tracing the Tropic of Cancer at its current latitude of approximately 23°26′N, it traverses a diverse landscape, passing through 17 countries (including two disputed territories) and eight distinct water bodies. Beginning at the prime meridian and moving eastward, the journey unfolds as follows:

  • Algeria: The Tropic makes its first landfall in Algeria, a vast North African nation.
  • Niger: It then crosses into Niger, a landlocked country known for its arid beauty.
  • Libya: Next, it passes through Libya, another significant player in the Sahara Desert landscape.
  • Chad: The Tropic briefly touches the northernmost point of Chad, a country often overlooked but geographically crucial.
  • Egypt: It then enters Egypt, famously passing through the expansive Lake Nasser .
  • Red Sea: The line of latitude then cuts across the Red Sea , a vital waterway connecting Africa and Asia.
  • Saudi Arabia: It traverses Saudi Arabia, crossing through the provinces of AlMedinah , Mecca , ArRiyadh , and The Eastern provinces.
  • United Arab Emirates: The Tropic then skirts the northern edge of the Abu Dhabi emirate in the United Arab Emirates.
  • Oman: It continues into Oman, even passing through the vicinity of its capital, Muscat .
  • Indian Ocean: The vast expanse of the Indian Ocean , specifically the Arabian Sea , is the next watery domain.
  • India: The Tropic then carves its path through India, affecting the states of Gujarat , Rajasthan , Madhya Pradesh , Chhattisgarh , Jharkhand , and West Bengal .
  • Bangladesh: It crosses into Bangladesh, impacting the Khulna , Dhaka , and Chittagong divisions.
  • India (again): The line re-enters India, specifically the state of Tripura .
  • Bangladesh (again): It then passes through Bangladesh once more, within the Chittagong Division .
  • India (yet again): Another brief passage through India, this time the state of Mizoram .
  • Myanmar: The Tropic then enters Myanmar, crossing through the Chin State , Sagaing Division , Mandalay Division , and Shan State .
  • China: It then makes landfall in China, affecting the provinces of Yunnan (passing remarkably close to the border with Vietnam ), Guangxi , and Guangdong .
  • Taiwan Strait: The line then navigates the Taiwan Strait , the body of water separating mainland China from Taiwan.
  • Taiwan: It crosses the island of Taiwan, impacting Hujing Island (Huching Island), Chiayi County , and Hualien County .
  • Philippine Sea: The Tropic then ventures into the Philippine Sea .
  • Pacific Ocean: It continues across the immense Pacific Ocean , passing just south of Necker Island in the US state of Hawaii .
  • Mexico: On the other side of the vast Pacific, the Tropic reappears in Mexico, specifically the state of Baja California Sur .
  • Gulf of California: It then crosses the Gulf of California .
  • Mexico (again): The line traverses mainland Mexico, passing through the states of Sinaloa , Durango , Zacatecas , San Luis Potosí , Nuevo León , and Tamaulipas .
  • Gulf of Mexico: It then enters the Gulf of Mexico , narrowly missing the southern coast of Cuba .
  • Atlantic Ocean: The Tropic then crosses the Atlantic Ocean , navigating through the Straits of Florida and the Nicholas Channel , passing south of the Anguilla Cays (part of The Bahamas ), and continuing through the Santaren Channel .
  • The Bahamas: It then passes through the Exuma Islands and Long Island in The Bahamas .
  • Atlantic Ocean (again): The journey continues across the open Atlantic Ocean .
  • Western Sahara: Emerging from the Atlantic, the Tropic touches the disputed territory of Western Sahara , claimed by both Morocco and the Sahrawi Republic .
  • Mauritania: It then enters Mauritania.
  • Mali: The line crosses into Mali.
  • Algeria (again): Finally, it re-enters Algeria before heading back into the vastness of the Atlantic.

Climate

The climate along the Tropic of Cancer is, for the most part, a study in extremes: hot and dry. However, there are exceptions. Cooler highland regions, particularly in China, offer a respite from the heat. Marine environments, like those found in Hawaii, and the eastern coastal areas experience significant orographic rainfall , with some locations receiving an astonishing 4 meters of precipitation annually.

Most regions situated on or near the Tropic of Cancer endure two primary seasons. The summer is intensely hot, with temperatures frequently soaring to 45°C (113°F). The winter, by contrast, is warm, with daytime highs around 22°C (72°F). Much of the landmass directly on or adjacent to the Tropic of Cancer is part of the formidable Sahara Desert . Further east, the climate shifts to a torrid, monsoonal pattern, characterized by a brief wet season from June to September, followed by prolonged periods of very little rainfall.

The highest peak that lies on or directly beside the Tropic of Cancer is Yu Shan in Taiwan . During the Last Glacial Maximum , glaciers on Yu Shan extended down to an impressive 2,800 meters. Even today, glaciers persist in proximity to the Tropic. The closest active glaciers are the Minyong and Baishui glaciers, located in the Himalayas to the north, and on Pico de Orizaba in Mexico, to the south.

Circumnavigation

For those with a penchant for extreme record-breaking, the Tropic of Cancer plays a crucial role in defining a circumnavigation. According to the stringent rules set by the Fédération Aéronautique Internationale , any flight aiming for a round-the-world speed record must cover a distance at least equal to the length of the Tropic of Cancer. Furthermore, it must cross every meridian and conclude precisely at the point of origin.

The precise length of the Tropic of Cancer is calculated at 36,788 kilometers (22,859 miles). The formula used for this calculation takes into account the Earth’s equatorial radius and the latitude of the Tropic:

$l=2\pi \cos(\varphi)6378137(1-0.00669438(\sin(\varphi))^{2})^{-0.5}$

where $\varphi$ represents the latitude of the Tropic of Cancer. For less official, more general circumnavigation attempts, these rules are somewhat relaxed, with a minimum distance requirement set at a rounded figure of 36,770 kilometers (22,850 miles).

(A selection of images depicting signs and markers indicating the Tropic of Cancer across various locations has been omitted for brevity, but would typically be included here in a full Wikipedia article.)

See also