How the Tropic of Cancer and the Tropic of Capricorn Where Named

Digitally manipulated image of North and South America from space over the Equator.
Ian Cuming/Getty Images

The Tropic of Cancer was named because at the time of its naming, the sun was positioned in the Cancer constellation during the June solstice. Likewise, the Tropic of Capricorn was named because the sun was in the constellation Capricorn during the December solstice. The naming took place about 2000 years ago and the sun is no longer in those constellations at that time of year.  At the June solstice, the Sun is in Taurus and at the December solstice, the sun is in Sagittarius.

Why Are the Tropics of Capricorn and Cancer Important?

Geographic features like the equator are fairly straightforward but the Tropics can be confusing. The Tropics were marked off because they are both places within the hemisphere where it is possible to have the sun directly overhead. This was an important an important distinction for ancient travelers who used the heavens to guide their way. In an age when our smartphones know where we are at all times, it's hard to imagine how hard getting around used to be. For much of human history, the position of the sun and stars was often all explorers and traders had to navigate by. 

Where Are the Tropics? 

The Tropic of Capricorn can be found at latitude 23.5 degrees south. The Tropic of Cancer is at 23.5 degrees north. The equator is the circle where the sun can be found directly overhead at noon. 

What Are the Major Circles of Latitude?

Circles of latitude are an abstract east and west circle that connects all places on Earth.

Latitude and longitude are used like addresses for every part of the globe. On maps latitude lines are horizontal and longitude lines are vertical. There is an infinite number of latitude circles on earth. Arcs of latitude are sometimes used to define the boundary between countries that lack distinctive geographic borders like mountain ranges or deserts.

There are five major circles of latitude.

  • Arctic Circle
  • Tropic of Cancer
  • Equator
  • Tropic of Capricorn
  • Antartic Circle

Living in the Torrid Zone

The major circles of latitude also serve to mark the boundaries between the geographical zones. The zone between the Tropic of Cancer and the Tropic of Cancer is known as the Torrid Zone.  In the United States, this area is more commonly known as the tropics. This area comprises almost forty percent of the globe. It is projected that by the year 2030, half of the global population will live in this area. When one considers the climate of the tropics it's easy to see why so many people want to live there. 

The tropics are known for their lush green vegetation and moist climate. Average temperatures range from warm to hot year round. Many places in the tropics experience rainy seasons which range from one to several months of consistent rainfall. Incidents of malaria tend to rise during rainy seasons. Some areas in the tropics such as the Sahara desert or Australian outback are defined as "dry" rather than "tropical".