Solar and lunar eclipses occur periodically due to the relative alignment of the Earth, Moon, and Sun following regular cycles known as saros cycles and metonic cycles.
The Moon orbits around the Earth, and our planet in turn orbits around the Sun. The journey of the Earth around the Sun lasts about 365 days, giving rise to our seasons and the variation of days and nights. As for the Moon, it completes its terrestrial orbit in about 29.5 days, creating the famous lunar phases we notice each month (full moon, new moon...). It is precisely this regular cosmic ballet that sometimes places the Moon directly between the Earth and the Sun, or conversely places the Earth exactly between the Sun and the Moon, making these spectacular solar and lunar eclipses possible.
For an eclipse to occur, a perfect alignment of Sun-Earth-Moon is absolutely necessary. The idea is simple: the Moon must position itself directly between the Sun and the Earth to cause a solar eclipse, or the Earth must slide exactly between the Sun and the Moon for a lunar eclipse to take place. But be careful, this doesn't happen just anytime: these celestial bodies must also be aligned precisely on the same line (the famous axis), otherwise, the event simply does not occur. Due to this requirement for precise alignment and the inclinations of the orbits, eclipses remain rare and fascinating rather than commonplace.
The lunar orbit is slightly inclined, by about 5 degrees, relative to the plane on which the Earth revolves around the Sun. It may seem small, but it's enough for the Moon to spend most of the time above or below the line between the Earth and the Sun. As a result, there is no eclipse every month. Eclipses only occur when the Moon passes precisely or very close to the lunar nodes, these two points where its orbit intersects the plane of the ecliptic. These crossings, which happen at regular intervals, explain why eclipses appear periodically and not randomly.
Eclipses are not simply random events; they occur according to well-known regular cycles. The most famous is undoubtedly the Saros cycle, which lasts approximately 18 years, 11 days, and 8 hours. This cycle is related to the fact that the Moon, Earth, and Sun return to almost identical relative positions after this specific period. Thanks to the Saros, one can predict when a similar eclipse will return, but since the cycle does not align perfectly with an integer number of days, each new eclipse shifts its geographical position on Earth. Other cycles also exist, such as the Metonic cycle, of about 19 years, which indicates the repetition of lunar phases on the same date of the solar calendar. These periodic patterns allow scientists, as well as enthusiasts, to accurately anticipate when and where to observe the upcoming eclipses.
Eclipses can be predicted well in advance thanks to our precise knowledge of the Earth's and the Moon's orbital movements. Since their orbits are quite regular, it is easy to anticipate the exact position of these celestial bodies on a given date. Astronomers particularly use the Saros cycle, a period of about 18 years during which eclipses occur in a similar order, making the prediction task much simpler. With modern tools, astronomers can even predict to the minute when the next eclipse visible from your window will take place. It's pretty amazing in terms of precision.
The reddish color of the Moon during a total lunar eclipse comes from the refraction of sunlight through the Earth's atmosphere, which is why it is poetically called the 'Blood Moon'.
A total solar eclipse can last no longer than 7 minutes and 32 seconds at a specific location on Earth. The reason? This is due to the apparent sizes of the Sun and the Moon, as well as their relative speeds in the sky!
Did you know that solar eclipses can have a noticeable effect on wildlife? Some animals, such as birds and insects, suddenly become silent or return to their resting places, thinking that night is falling!
Lunar eclipses can be seen by all the inhabitants of the night half of the Earth, unlike solar eclipses, which are only visible in a narrow band called the 'path of totality.'
Even though a lunar eclipse occurs during a full moon, most full moons happen when the Moon is slightly above or below the Earth's orbital plane (the Sun-Earth line). A lunar eclipse only appears when the Moon passes directly through or very close to the lunar nodes.
The Saros cycle is a period of about 18 years and 11 days, after which solar and lunar eclipses occur in a similar order. It is a fundamental period that helps to accurately predict future eclipses on Earth.
A total solar eclipse occurs when the Moon completely covers the solar disk as seen from Earth. A partial eclipse happens when the Moon partially passes in front of the solar disk. Finally, an annular eclipse occurs when the Moon is farther from the Earth, appearing too small to completely hide the sun, leaving a visible solar ring.
Because the Earth rotates on its axis while orbiting around the Sun, and the Moon orbits around the Earth. These combined movements shift the lunar shadow (or penumbra) across different regions of the Earth in a uniquely different way each time.
At most, there can be seven eclipses in a year (including both solar and lunar eclipses), and at least four. This depends on the alignment of the Sun, Earth, and Moon, as well as the relative position of the lunar nodes.
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