During this May 23, 24 and 25, some cities in Mexico will be left in darkness due to a strange and particular astronomical phenomenon. In popular culture it is known as the ‘day without a shadow’, although many specialists call it Sol Zenital.

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According to the Institute of Astronomy of the Autonomous University of Mexico (UNAM), the Zenithal Sun appears when this star goes upright. That is, at the highest point in the sky.

Once the Sun reaches its zenith, just above the Earth, no side shadow is cast for a few minutes. Although it is a natural astronomical phenomenon, it only occurs a few days a year, and the date differs depending on the latitude or angular distance between the equator and a given point on the planet.

“This phenomenon occurs when the Sun is exactly over our heads, at a point on the celestial vault called the zenith,” explains Santiago Vargas Domínguez, Research Coordinator of the National Astronomical Observatory (OAN) of the National University of Colombia for the agency. institution news.

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During the ‘shadowless day’ the Sun is located in a vertical position.

And he adds: “The moment without a shadow is temporary, and the Sun, by following its apparent movement in the firmament, makes the shadows of the objects gradually reappear.”

The expert points out that the ‘day without a shadow’ has taken place hundreds of years ago, when the Sun began to orbit the Earth and the axis of its orbit tilted approximately 23.5º with respect to the plane of the orbit.

This terrestrial inclination produces, according to the UNAM, that during the equinoxes the Sun appears just at the zenith of the equator, to later rise about 23°27′ at the summer solstice and lower the same amount at the winter solstice, the which takes place at the end of December.

In this line, the sun’s rays fall perpendicularly on the Tropic of Capricorn because the northern hemisphere of the Earth is tilted in its maximum degree in the opposite direction to the Sun.

When and where can it be seen?

Depending on the inclination of the Earth’s axis of rotation, the Zenithal Sun occurs in regions located near the Earth’s equator. Experts point out that the astronomical phenomenon is only perceptible in territories located south of the Tropic of Cancer and north of the Tropic of Capricorn, at latitudes 23.5°.

“The Sun at the zenith occurs when the latitude of a site coincides with the declination of the Sun”, points out the researcher and astronomer Eddie Salazar Gamboa for the portal ‘Enséñame de Ciencia’.

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In Uxmal, Yucatán, the ‘day without a shadow’ took place on May 23 and on the 24th it passed through Chichén Itzá. This May 25, the Zenital Sun will be present both in Mérida and in Dzibilchaltún.

The star acquires the zenithal position only twice a year. However, the dates are not always the same. To have an approximate of when the phenomenon will occur, it is necessary to use an analemma, a diagram that explains the curve that describes the position of the Sun in the sky.

El Sol Cenital will take place on May 25 in Dzibilchaltún.

“In the tropics of Cancer and Capricorn, one zenithal day a year can be recorded, while in the intertropical zones there are two opportunities to see it. If we are at a latitude above the Tropic of Cancer, or below the Tropic of Capricorn, there will be no zenithal day during the year,” Domínguez details for the National University news agency.

Guatemala, unlike the rest of the countries, is the only one where the zenithal day occurs on exact dates: one on April 30 and another months later, on August 9 of every year.

Last Saturday, April 1, 2023, Bogotá lived a ‘day without a shadow’ and Medellín did on April 5. In both cities, the shadows were temporarily absent to make way for the Zenital Sun.

The importance of ‘Shadowless Day’ in ancient cultures

Although one tends to think that this astronomical phenomenon lacks relevance, the reality is that it has great scientific and astronomical value, not in vain has it acquired various functions and connotations over the years.

The Egyptians and Mayans, for example, used the ‘shadowless day’ to determine the location of temples and structures. Some of these aboriginal cultures even saw in the Zenital Sun the materialization of a divinity, as well as a symbol of power, respect and greatness.

It is said that these groups held meetings on this date that were intended to commemorate the star and receive its energy, taking into account that it rested on the zenith.

The data collected from this phenomenon have been used to study the atmosphere.

Currently, the importance of the Zenital Sun transcends ancient cultures and is gaining ground in the scientific field because its data can be used to study the Earth’s atmosphere and ionosphere. This is how Professor Domínguez explains it.

“Taking into account that when the Sun is at its zenith and the solar rays pass through the least amount of atmosphere, data can be taken from this phenomenon. For example, it can be used to study the propagation of radio waves through the atmosphere and the ionosphere”, said the expert to the aforementioned medium.

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Original Publisher: https://www.eltiempo.com/cultura/gente/dia-sin-sombra-en-que-consiste-fenomeno-que-dejara-a-oscuras-a-pais-de-latinoamerica-771378