The combination of the Sun, the Earth, and the Moon is truly magnificent, bringing us such spectacular astronomical phenomena as solar eclipses and lunar eclipses. In ancient times, when solar or lunar eclipses occurred, people would panic or feel confused, believing they would bring disaster. Later, people learned that solar and lunar eclipses are regular astronomical phenomena.
When the Moon moves between the Earth and the Sun, it blocks the Sun, creating a shadow. The shadow can be divided into the umbra, the penumbra, and the antumbra. In the umbra, the Sun is completely blocked, and we see a total solar eclipse; in the penumbra, the Sun is only partially blocked, and we see an annular solar eclipse; while in the antumbra, the center of the Sun is blocked, but the light from the Sun's edge is not blocked, so we see an annular lunar eclipse. When a solar eclipse occurs, the shadow of the Moon sweeps across the Earth's surface, forming a solar eclipse zone. People within this zone can enjoy the solar eclipse at different times. There is also a very special solar eclipse phenomenon, namely the total annular solar eclipse. When this solar eclipse occurs, some areas within the solar eclipse zone can see a total solar eclipse, while people in other areas see an annular lunar eclipse. China was one of the earliest countries in the world to observe and record solar eclipses, and the earliest records of solar eclipses date back more than 4,000 years.
Similarly, when the Earth moves between the Moon and the Sun, the Moon enters the Earth's shadow, and a lunar eclipse occurs. Lunar eclipses are divided into partial lunar eclipses, total lunar eclipses, and penumbral lunar eclipses. Since the Earth's shadow is much larger than the Moon's angular diameter, there is no annular lunar eclipse. The most beautiful lunar eclipse phenomenon is the total lunar eclipse, which occurs when the Moon completely enters the Earth's umbra. During a total lunar eclipse, the entire Moon turns a bronze color. It looks particularly beautiful against the backdrop of the stars. Before and after a total lunar eclipse, there will also be a partial lunar eclipse process. A partial lunar eclipse occurs when the Moon partially enters the Earth's umbra. During a penumbral lunar eclipse, the brightness of the Moon's surface changes little and is not easily noticed by people.
Although the occurrence of solar and lunar eclipses varies from year to year, through long-term observation, recording, and calculation, people have summarized the laws of solar and lunar eclipses. More than 2,000 years ago, the Babylonians discovered the "Saros cycle", which lasts about 6,585.32 days, or about 18 years and 11 days. "Saros" is the Latin word for "repetition", because every Saros cycle, the Moon will return to the same point in its relative position to the Earth and the Sun. That is to say, if a solar or lunar eclipse occurs at a certain moment, then after a Saros cycle, the same solar or lunar eclipse will occur again. However, due to the "tail" of 0.32 days in the Saros cycle, if a solar or lunar eclipse occurs in a place, it will not occur again in the same place until after three Saros cycles, or about 54 years later. The Saros cycle is actually a multiple of three lunar cycles: the synodic month (the cycle of the Moon's phases), the nodal month (the cycle of the Moon's return to the intersection of its orbital plane and the ecliptic plane), and the perigee month (the cycle of the Moon's return to its perigee). In the Han Dynasty of China, a solar and lunar eclipse cycle was also discovered, called the "Three-Generation Calendar Cycle", which lasts 3,986.62965 days, which is roughly equivalent to 146.5 nodal months. Nowadays, scientists can calculate in more detail when and where we can see what kind of solar or lunar eclipse phenomena. This time is even more accurate than the watches we use.