If you remember elementary school classes you surely have in your mind the image of the teacher spitting out information saying that there were two, in fact three parallels that deserved more attention than the others. The Tropics of Capricorn, the Cancer and the most famous the Equator.
But when asked why there were the tropics of Capricorn and Cancer, if her teacher was like mine, she simply said that it was where the tropical countries were!
The Ecuador line is more obvious, it divides the world into two. But to know why these two “special” parallels exist, we first have to know what are two natural phenomena caused by the inclination of the globe in its rotation which are:
EQUINOX: From the Latin “aequus, igual” and “nox, noche” or length of day is the same as the duration of the night, ie the duration of the sunrise until its by is equal to the duration of the sunset until his birth. This occurs twice a year, one in autumn and one in spring.
SOLSTICE: From Latin “sun + sistere”, sun that does not move. The Summer Solstice is the longest day of the year. It occurs only once in summer in every hemisphere of the planet. For those who do not know, when it is summer in the northern hemisphere and winter in the southern hemisphere, and vice versa. And when in one hemisphere they are in the Summer Solstice, conversely in the other they are in the Winter Solstice which is the longest night of the year.
But finally, what are these Tropics:
In the natural phenomenon of the Solstice (longest day), the line where the sun, at around noon, strikes completely perpendicularly, when the shadow of a straight body disappears beneath itself, is exactly the Tropic of Capricorn in our summer or exactly in the Tropics of Cancer in the summer of the northern hemisphere. See the illustration above, shows the incidence of sun rays totally perpendicular to the globe, in the Tropic of Cancer.
The tropic of Capricorn moves, but very slowly, to the north, at the rate of 15 meters per year. Those road signs that we see on some roads saying, HAPPENS THE TROPIC OF CAPRICORN, should be moved north every year, I doubt they do. The Tropic of Cancer also has its variation.
The ancient civilizations already knew these phenomena marking the dates with popular celebrations that were appropriated by very famous religions like the arrival or death of their unlikely gods. If in doubt ask about it.
And not only in the old world, on the side of the Ocean, a land forgotten by some very sacred books, the pyramid of Kukulcan, located in the archaeological city of Chichen Itza in the Mexican state of Yucatan, is a stone calendar built by the Mayans mark the Solstices and the Equinoxes.