Perhaps readers may experienced those boring geography lessons in stuffy classrooms students wanted to escape? If so, you may recall some mention of the Tropic of Cancer. Or maybe you remember the mention of the Northern Tropic, this being an alternative name for the Tropic of Cancer. Both names highlight the northern location of this latitudinal line, with Cancer being the constellation in which the sun lay on the June solstice in ancient times. While the sun no longer sits in Cancer, at present it being in Gemini, the name has been used in Western academia for over 2,000 years. Since the concept of the Tropic of Cancer was discovered, along with its southern twin the Tropic of Capricorn, was postulated, and so there is no going back. With this said what exactly is the Tropic of Cancer? Here we consider this very question.
The Tropic of Cancer is the latitudinal line that marks the farthest northern latitude at which place the sun appears to turn after reaching its declination, or zenith.
What Exactly Does That All Mean?
At its most simple definition, the Tropic of Cancer is an imaginary line that sits at a latitude of 23.5 degrees north of the equator. This latitude marks the last point where the sun appears directly overhead at its zenith (its highest point) on the June or Summer Solstice (also known as the Midsummer or Festival Solstice). Due to the curvature of the earth, as well as the axial tilt (or obliquity), anywhere farther north than the Tropic of Cancer, on the June Solstice, will observe the sun to not be directly overhead (that is not at an elevation angle of 90 degrees) when at its highest point in the sky.
Where is the Tropic of Cancer?
The Tropic of Cancer is found at a latitude of 23.5 degrees north of the equator (making it 42.5 degrees south of the Arctic Circle). It runs across three continents and through 16 countries, these countries being Mexico, the Bahamas, Myanmar, the Western Sahara, Oman, Mauritania, Mali, Algeria, Libya, Egypt, Saudi Arabia, the United Arab Emirates, India, and China. It also runs through six major bodies of water, these being the Indian Ocean, Atlantic Ocean, Pacific Ocean, Taiwan Strait, Red Sea, and Gulf of Mexico.
The region between the Tropic of Cancer and the Tropic of Capricorn is known as the Torrid Zone or the Tropics. This region is characterized by being much warmer, and having a higher humidity, than those regions latitudinally above the Tropic of Cancer, or below the Tropic of Capricorn. This region contains almost 40% of the global population at present and by the end of the decade, it is projected that this number will increase to over 50%.
Why is it Important?
Before humans had access to GPS, and other radar navigation systems, knowledge of the celestial bodies, and how they appeared at different points around the earth was used to navigate across land, especially across bodies of water. Without this knowledge, traders and explorers would not have been able to travel to foreign lands, which is one of the things that helped propel humans from our hunter/gatherer ancestors towards communities with much larger populations.
Trade routes helped humans exchange their knowledge and technologies, pushing man out of the Stone Age and into the more technologically advanced Bronze and Iron Ages, and so on.
For example, those who live at a mid-north latitude from the equator observe the sun at its zenith (this being around noon depending on daylight savings) somewhere in the southern sky close to the Summer Solstice. Knowledge of this means that if lost, individuals can orient themselves based upon the sun’s position in the sky. If needing to head north, travel with the sun behind you. If traveling south, follow the sun to your destination. Of course, there is a bit more to it, but at its foundation, celestial navigation is based upon this principle.
Throughout the year, the angle of the sun’s rays changes which in effect giving us distinct seasons. The farther north or south you go, meaning the farther away from the equator you are, especially past the latitudinal Tropics lines, the more drastic a change in the angle of the sun’s rays and therefore more distinct seasonal temperature changes are observed. This larger temperature differential creates more distinct seasons.
Today, knowledge of the Tropic of Cancer may appear less important than it once was, however, without this knowledge industries, from farming and agriculture to airplane ground and sky navigation and transcontinental ocean shipping, would never have advanced to their present states. In many hidden ways, we owe a great deal to those who postulated the idea of the Tropic of Cancer, and the Tropic of Capricorn, over 2,000 years ago.