Tomorrow, April 8, for a few minutes the day will turn into night along the path of the total solar eclipse that will cross North America, describing a great arc from the west coast of Mexico to the extreme northeast of Canada. Millions of people, in cities as important as Dallas, Austin, Indianapolis or Cleveland, will watch the Sun disappear behind the lunar disk while they perceive an abrupt decline in temperature and see stars appear in a darkened daytime sky.
The so-called Great American Eclipse will be the most viewed in history. And total solar eclipses rarely cross such populated regions with so many mobility options. According to the United States Department of Transportation, about 32 million people live along the path of so-called totality (the area in which the Sun will set completely).
Large crowds are also expected on the roads. The North American Department of Transportation expects that some 5 million people will go, during the hours before the eclipse, to the areas with the best visibility, and the worst traffic jams are predicted for when the phenomenon ends (in the previous North American eclipse, in 2017, there were delays of more than 15 hours and queues of a hundred kilometers on some communication routes).
Tomorrow's event is a preview of what can be experienced in Spain with two total solar eclipses in a row that will take place on August 12, 2026 and August 2, 2027.
Solar eclipses occur when the Moon comes between the Earth and the Sun, obscuring it. Although, by definition, in a solar eclipse the lunar phase is new (the side of the Moon that is illuminated by the Sun is the one that we cannot see from our planet), not all new moons generate eclipses. The reason must be sought in the inclination of the satellite's orbit with respect to the Earth-Sun plane, which generally means that the new moon transits above or below the solar disk without obscuring it.
Thus, the eclipse can only occur when the new moon phase occurs exactly above the plane of the Earth's orbit around the Sun, in the so-called ascending node (when our satellite crosses the plane of the Earth's orbit from bottom to top) and descending node.
But the gift of the solar eclipse is also made possible by a lucky coincidence. By chance, the size with which we see the lunar disk in the sky coincides, almost exactly, with that of the Sun. That is, the dimensions of our satellite and our star, as well as the distances that separate us from these bodies are the ideal so that the Moon, seen from Earth, can completely hide the king star.
In so-called total solar eclipses, the Sun is completely hidden by the Moon. Its shadow is projected on the surface of our planet and, due to the Earth's rotation, it moves towards the east at a speed of approximately 3,200 kilometers per hour on routes that are usually thousands of kilometers long but with so only a few hundred wide.
In a partial eclipse, only a portion of the solar disk is covered. In fact, in the stripes that are on each side of the path of the shadow of a total eclipse, the phenomenon is perceived as partial. The coverage regions of the partial eclipse are much larger than those of the totality.
The solar eclipses that occur when the Moon is at its furthest orbital point from the Earth are called annular: our satellite is seen with a slightly smaller size and, at the peak of the eclipse, its silhouette is surrounded by a spectacular sunlight ring
There are few natural events that provoke as much fascination as that which is concentrated in the few minutes that totality lasts. A solar eclipse like tomorrow's begins as a partial one, when the dark disk of the Moon begins to bite into that of the Sun. As the phenomenon progresses, the hidden solar portion becomes increasingly larger.
The climax, that of totality, arrives abruptly when a last ray of sunlight escapes through the limb of the Moon's disk, generating a characteristic flash. Next, night falls in broad daylight and that is when, around the hidden disk of the Sun, the filaments of its corona can be seen (an extraordinarily hot region that surrounds the star), and the brightest stars appear in the sky. The drop in temperature, depending on local conditions, can be up to a dozen degrees.
The end of the total phase comes as suddenly as it began. A new flash of light, which emerges just on the opposite side of the dark disk of the Moon and generates the so-called diamond ring, once again illuminates the landscape and from that moment on the Sun becomes more and more uncovered as the silhouette of the Moon moves.
It is important to remember that to observe a solar eclipse, approved instruments are required to avoid serious eye injuries, and it is only possible to contemplate the phenomenon with the naked eye in the brief moments that totality lasts.
Tomorrow's eclipse will enter the American continent along the west coast of Mexico, at exactly 12:51 local time, and its totality phase will advance towards the border with the United States, entering this country through the state of Texas and moving northeast through the states of Oklahoma, Arkansas, Missouri, Illinois, Kentucky, Indiana, Ohio, Pennsylvania, New York, Vermont, New Hampshire and Maine. From there, it will go to Canada where it will travel through part of the provinces of Ontario, Quebec, Nova Scotia and, finally, Newfoundland and Labrador.
The eclipse will touch the northeastern tip of America at 5:16 p.m. local time. Throughout this route, the total phase can be observed from places as charismatic as Niagara Falls. A detailed and interactive map of the eclipse passage, with start, end and totality times for any location, can be consulted at this link.
It so happens that this phenomenon coincides with the position in the daytime sky of five planets and a comet. Thus, when the star is hidden and the sky darkens, it will be possible to glimpse the bright Venus and Jupiter and also the fainter Mercury, Mars and Saturn. For its part, comet 12P/Pons-Brooks, which is approaching the interior of the solar system at this time, will appear very high in the sky and at a short visual distance from the Sun.
