Lunar and solar eclipses stand as some of the oldest natural phenomena known and observed by humans. These extraordinary events occur at specific times, under certain circumstances, and in precise locations, as a result of the orbits of Earth and the Moon, which lead to one celestial body obscuring the sunlight from reaching the other. To the observer, it appears as though the sun has lost some of its brightness or the moon has relinquished a portion of its glow.
Lunar Eclipse: Definition and Causes
A lunar eclipse takes place when Earth obstructs sunlight from reaching the Moon. This means the lunar eclipse occurs when Earth's shadow falls on the surface of the Moon, which can be total, partial, or penumbral.
Types of Lunar Eclipse
Total Lunar Eclipse
A total lunar eclipse happens when the Sun and Moon are directly opposite each other with Earth in between. Even though the Moon is entirely within Earth's shadow, a quantity of sunlight still reaches it through Earth's atmosphere, which scatters most of the short-wavelength light such as blue and violet, while the longer-wavelength red light passes through. This is why the Moon appears red, often referred to as a "Blood Moon."
Because Earth's diameter is about four times that of the Moon, its shadow is much larger, allowing a lunar eclipse to last for over 100 minutes in extreme cases.
Partial Lunar Eclipse
A partial lunar eclipse occurs when only a portion of the Moon enters Earth's shadow. Depending on the extent of the eclipse, a reddish tint may appear on the darkened part of the Moon's surface. While total lunar eclipses are rare, partial lunar eclipses can happen at least twice a year.
Penumbral Lunar Eclipse
This phenomenon takes place when the Moon passes through Earth's faint outer shadow, resulting in such a subtle eclipse that it's hard to detect with the naked eye. Visibility depends on the extent of the area entering the penumbral shadow; the smaller it is, the more difficult the eclipse is to see, which is why such events are usually excluded from most calendars, except for scientific ones.
Solar Eclipse: Definition and Causes
A solar eclipse occurs when the Moon passes between the Sun and Earth during its orbit, thereby casting its shadow onto the Earth. This leads to one of three types of solar eclipses, differentiated by how the Moon obscures the sunlight and the extent of the coverage.
Types of Solar Eclipse
Total Solar Eclipse
A total solar eclipse happens when Earth, the Moon, and the Sun align in such a way that the Moon completely blocks sunlight from reaching parts of Earth. For a brief moment, lasting a few minutes at times, the sky darkens to a point of resembling nightfall.
The total solar eclipse is quite rare. The Sun's diameter is 400 times greater than that of the Moon, and it is also about 400 times further from Earth than the Moon is from us. The exact alignment of these three bodies results in the Moon entirely obscuring sunlight, causing a total solar eclipse.
The path where the Moon's shadow falls on Earth is called the "path of totality." In this narrow strip, individuals can experience complete darkness. However, for thousands of kilometers on either side of this path, the eclipse can be seen partially. As one moves away from the "path of totality," the portion of the Sun obscured by the Moon decreases.
The duration of the phenomenon depends on Earth's position relative to the Sun, the Moon's position relative to Earth, and the area affected by darkness on Earth's surface. Theoretically, the longest total solar eclipse could last for 7 minutes and 32 seconds.
As for the frequency of total solar eclipses, they are not as rare as some might think, occurring approximately every 18 months. However, witnessing the event in the same place on Earth is exceedingly rare, repeating on average only every 375 years.
Annular Solar Eclipse
When the Moon is further away from Earth, it appears smaller to observers and thus doesn't cover the Sun completely. Instead, there remains a ring-like part of the Sun visible around the Moon, known as an annular solar eclipse.
Similar to a total eclipse, an "annular path" is formed where the eclipse can be seen as a ring. Deviations from this path result in regions where the phenomenon can be partially observed around the "annular path."
According to NASA, this type of eclipse lasts longer than the total solar eclipse, with the Sun's ring visible for more than 10 minutes in some cases, though typically they do not last more than 5 or 6 minutes.
Hybrid Solar Eclipse
This occurs when the Moon is at a distance where it can completely block the Sun, but as it moves along its path, it stops obscuring the Sun entirely and transitions to an annular eclipse.
Conversely, the eclipse may start as annular, and as the Moon approaches Earth, it can become a total solar eclipse.
Hybrid eclipses are quite rare, constituting only about 4% of solar eclipses, as per the Astrophysics Institute in the Canary Islands.
Circumstances of Lunar and Solar Eclipses
A lunar eclipse can only occur during a full moon, in the middle of the lunar month. Conversely, a solar eclipse can only take place when the Moon is in its new phase at the end of the lunar month.
While witnessing a solar eclipse depends on the geographic location of the observer, a lunar eclipse can be observed from any location on Earth where the Moon is above the horizon at the time of the eclipse.
Eclipses in Other Stellar Systems
The phenomenon of celestial bodies obscuring one another is not limited to the Moon and Sun; it also includes distant stars. Chilean astronomer Pemín notes that 50% of stars are in clusters consisting of binaries or multiple stars. Given the vast number of stars in our galaxy, some binary stars—those systems with two stars orbiting a common center of mass—in particular alignments eclipse each other as they orbit, concealing one from view. Such stars are known as "eclipsing binaries."
