Tropic of Cancer

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Tropic of Cancer (on the map is shown as the red line).

The Tropic of Cancer is one of the parallels of the planet that are located in the northern hemisphere, at a latitude of 23° 26' 10 north of the equator. It is moving south at a rate of almost half a second (0.46 s) per year (in 1917 it was at 23° 27').

This imaginary line joins the northernmost points where the Sun reaches the zenith (the vertical of the place), which occurs between June 20 and 22 of each year, during the so-called boreal summer solstice or southern winter. In astronomical tables, the date and time are indicated in Coordinated Universal Time (UTC).^{[citation required]}

At the instant the June solstice occurs, the sun's rays fall vertically on the ground on the imaginary line of the tropics of the northern hemisphere (Cancer). On the December solstice, they do so over the tropics of the southern hemisphere (Capricorn).^{[citation needed]}

The Tropic of Cancer marks the northern limit of the so-called intertropical zone, between the Tropics of Cancer and Capricorn.

Origin of name

It is called "of Cancer" because in ancient times, when the summer solstice occurred in the northern hemisphere, the Sun was in the constellation of Cancer. Currently, it is in the constellation of Taurus, very close to the edge of the constellation of Gemini. The Greek word τρόπος tropos comes from the Greek and means 'turn', indicating that, on the solstices, the Sun apparently stops, only to reverse its path days later.^{[ citation required]}

According to the dynamics of the precession of the solstices (and equinoxes), a little over 20 centuries ago the solstitial point was at the end of the constellation Cancer. The constellation following that of Cancer in a precessional sense is that of Gemini, which covers 28º of the ecliptic, and the solstitial point advances 1º every 71.6 years. Thus, during the last 20 centuries, the solstitial point has passed through Gemini and has now entered Taurus, in its first degree.^{[citation required]}

In the tropics at noon the rays from the Sun located in Taurus are received and for this reason this would be the astronomical name of the tropics, a name that provides astronomical information and the dynamics of the precession of the summer solstitial point of the Earth. It could also be called the "Taurus solstice." The same happens with the other solstice and the Tropic of Capricorn.^{[citation needed]}

Countries traversed

Highway 83 (Vía Corta) Zaragoza-Victoria, km 27+800 (Tamaulipas, Mexico). Of all the crossings of the Tropic of Cancer with the Mexican federal roads, this is the only place where latitude is marked with absolute precision and can also be visualized.

The Tropic of Cancer passes through the following countries, in alphabetical order: