Page:Illustrated Astronomy.pdf/70

 Today, we can predict eclipses in advance thanks to accurate calculations, using math formulae, and what we know about physics. In contrast, in the past, some civilizations could predict eclipses identifying different patterns in the lunar motions fruit of their acute observation power and their accurate notes about past events.

Around the 4th century BC, the wiser Chaldean astronomers/astrologists of the new Babylon identified what Greeks later would call saros, which was related to the period of 223 moons, in other words, 18 years, 11 days, and 8 hours. These wise people noticed that every time a saros happened, the position of the Sun, Earth, and Moon were alike and, therefore, the same series of eclipses repeated, but these would not be in the same place as Earth since the cycle doesn’t have whole numbers of days, but it has eight more hours. Within those eight hours, the Earth has rotated one-third (eight hours on the twenty-four a day has), and therefore the eclipse occurs in one-third of Earth towards the west. For instance, if today an eclipse in Concepción, Chile, occurs, in one saros should be in New Zeeland.

Based on this, one would expect that every three saros (something like 54 years) a new solar eclipse would happen in the same region. However, it is not entirely correct due to small differences, and other celestial motions related. In fact, on average, a region of the Earth experiences a total eclipse of Sun every three hundred years.

Nowadays, we know much better about the physics laws of celestial bodies, and the motions of the planets and their satellites are calculated precisely.

The Sun gravity forces, the eight planets and their satellites, asteroids, and dwarf planets are included to make more accurate calculations. Also, tidal effects, Earth distribution mass (which is not perfectly homogenous), and the terrestrial motions and precession and nutation, among others, are included in the motion calculations.

DID YOU KNOW THAT…

''the duration of an eclipse depends on Earth’s position compared to the Sun, on Moon’s in respect of the Earth, and on what Earth’s region is shade? Theoretically, the longer solar eclipse could last 7 minutes and 32 seconds. So far, the longest ever registered was on July, 15th of 743 B.C., and lasted 7 minutes, 28 seconds.''

On July, 16th of 2186, it is expected a total solar eclipse will pass over Venezuela, lasting 7 minutes, 29 seconds, becoming the longest eclipse since 4000 B.C., and it will be until the year 6000 A.D., at least. 70 • • •