On 12 August 2026, Spain will witness an extraordinary astronomical event: a total solar eclipse visible across much of the country. It will be the first total solar eclipse visible from the Iberian Peninsula in more than a century. It will also mark the beginning of a remarkable sequence, with another total eclipse taking place in 2027 and an annular eclipse in 2028, making Spain one of the best places in the world to experience these spectacular events.
Beyond the breathtaking display in the sky, the eclipse also raises an intriguing question for those who love the sea: could it affect the ocean? The answer is yes, but not in the way you might expect.
What actually happens during a total solar eclipse?
A total solar eclipse occurs when the Moon passes directly between the Sun and the Earth, completely blocking the Sun’s light for anyone standing within the narrow path traced by its shadow.
It is the result of an extraordinary cosmic coincidence. Although the Sun is around 400 times larger than the Moon, it is also about 400 times farther away from Earth. This makes both objects appear almost exactly the same size in our sky. As a result, for a few brief minutes, the Moon can completely cover the Sun’s disc, revealing the solar corona, the Sun’s faint outer atmosphere, normally hidden by the Sun’s overwhelming brightness.
Baily’s Beads appear when the last rays of sunlight shine through valleys in the Moon’s rugged terrain, just before the Sun’s disc is completely obscured by the Moon. Photo credits: NASA/Aubrey Gemignani.
For a short time, daylight fades as though dusk has arrived early. But a total solar eclipse is more than just a spectacular visual event. The same alignment of the Sun, Moon and Earth that makes it possible also plays a role in one of the ocean’s most fundamental processes: the tides.
Does an eclipse make the sea level rise?
The short answer is no. Or, more accurately, not because of the eclipse itself.
Tides are driven primarily by the Moon’s gravitational pull on Earth’s oceans. Although the Moon is much smaller than the Earth, its proximity means its gravity is strong enough to move vast masses of seawater, producing the tides we experience every day.
The Sun also exerts a gravitational pull on our planet. Although its effect on tides is much smaller than the Moon’s, when the two bodies are aligned their gravitational forces combine, producing what are known as spring tides, higher-than-usual high tides and lower-than-usual low tides.
And this is the key point: the eclipse itself does not make the tides any stronger than they would normally be. A total solar eclipse can only occur when the Sun, Moon and Earth are aligned, which is the very same configuration required for spring tides. In other words, the eclipse and spring tides are both consequences of the same alignment of these three celestial bodies.
However, this alignment is not unique to eclipses. It occurs naturally at every new moon and, in the case of spring tides, also at every full moon, roughly twice each month. The difference is that the Moon’s orbit is slightly tilted relative to Earth’s orbit around the Sun, meaning that in most cases the alignment is not precise enough to produce an eclipse. Only occasionally does the Moon’s shadow fall on Earth’s surface, creating a total solar eclipse.
Phases of totality of the Aug. 21, 2017, total solar eclipse observed from Salem, Oregon by the Williams College Expedition. Credit: Jay Pasachoff, Ron Dantowitz, Christian Lockwood, and the Williams College Eclipse Expedition/NSF/National Geographic.
When the ocean goes dark too
Although an eclipse does not, by itself, intensify the tides, it does temporarily alter another key factor for marine life: light.
For many marine organisms, light intensity acts as a cue that regulates essential activities such as feeding, resting and daily movements. During a total solar eclipse, daylight can suddenly fade for more than two minutes, creating conditions similar to dusk in the middle of the day.
Could this temporary darkness affect marine life? Although research in this area is still limited, some studies have reported short-lived behavioural changes in certain marine organisms during solar eclipses. For example, some species have been observed displaying behaviours normally associated with dusk in response to the sudden reduction in light. However, responses vary between species and ecosystems, and much more research is needed to understand how these brief periods of darkness influence marine life.
For this reason, solar eclipses provide scientists with a valuable natural experiment for investigating how light shapes the behaviour of marine organisms.
More than a spectacle in the sky
On 12 August, millions of people will look up to witness the total solar eclipse. At SUBMON, we invite you to make the journey in the opposite direction too and turn your attention towards the ocean.
For a few brief minutes, the eclipse reminds us that the ocean does not exist in isolation. The gravity that drives the tides and the light that regulates the rhythms of countless marine organisms are just two examples of how phenomena we observe in the sky can also help us understand what happens beneath the surface of the sea.
If you’ll be watching the eclipse from the coast or from a boat, we’d love to hear about your experience. Share your photos, videos or any observations of how you experienced the eclipse at sea by emailing comunicacio@submon.org or through our social media channels.
