One of the most spectacular events in the sky could be witnessed by skywatchers in a century: a full solar eclipse that transforms day into night. NASA claims that a unique combination of cosmic geometry could make the 2186 solar eclipse one of the longest ever documented.
The Moon passes exactly between the Sun and the Earth during a total solar eclipse, creating a small shadow where light briefly turns to darkness. The alignment of the Moon and Earth in 2186 will be unique because it is expected that the Moon will be close to Perigee, which is its closest point to Earth, and that Earth will be close to Aphelion, which is its furthest point from the Sun. This combination is perfect for a longer totality because it makes the Moon appear slightly bigger and the Sun appear slightly smaller in our sky.
Time and distance are essential factors in astronomy, and precise astronomical forecasting help the researchers to predict eclipse paths and durations well in advance. According to cartographer Michael Zeiler, a totality of approximately 7 minutes 29 seconds would reach the physical limit of the amount of time that the Sun can be blocked. However, experts remind us that even though models are very good, as we refine the data, long-range estimates may change a bit.
Why 2186 could last so long
Total eclipses typically last only a few minutes. A number of things need to coincide for that to be stretched into seven-plus:
- Perigee: The Moon appears larger and is better able to completely cover the Sun when it is closer.
- Aphelion: The Sun appears somewhat smaller when the Earth is farther from it, which also encourages longer coverage.
- Near the equator: To extend the duration of the shadow, an eclipse path should be located close to the equator.
- Motion and rotation of the shadow: Darkness can stay at a single spot for a longer period of time if the Moon’s shadow moves in parallel with Earth’s rotation.
All of these elements should line up on July 16, 2186. How would it feel? As if someone had flipped a huge lighting switch, the midday light would go out. The temperature may slightly drop. The shadows would grow longer and more intense. The animals could be quiet. Then daylight would come back as fast.
How scientists predict it
Highly precise astronomical prediction models that monitor the movements of the Earth, Moon, and Sun provide eclipse forecasts. Although these models are very good, there are small uncertainties when looking hundreds of years into the future. The timing or exact trajectory may be slightly modified by small shifts in the Earth’s rotation, the Moon’s motion, or gravitational pulls. Scientists will continue to fine-tune details over time, which is why they refer to the 2186 estimates as the “best prediction” for the time now.
The obvious conclusion is that this may be one of the longest total solar eclipses in thousands of years. Importantly, observers will only be able to see totality along a limited route; beyond that, they will see an impressive partial bite out of the Sun, which is not the same as day turning to night.
A rare show, explained by science
An excellent illustration of how astronomy can make the cosmos seem more intimate and tangible is the solar eclipse of 2186. Totality might last exceptionally long, pushing the established boundaries that experts like Michael Zeiler outline, if the Moon is at Perigee, the Earth is close to Aphelion, and a path is perfectly aligned.
Even though we acknowledge that long-range numbers may change slightly as models are updated, NASA and contemporary astronomical prediction allow us to understand the “how” and “why” well in advance.