Neither Day nor Night; What Eclipses Teach Us About the Sun

Imagine you're out in the countryside.

The sun is shining brightly.

Suddenly, the light begins to dim. The shadows shift, the air seems to grow cooler, birds stop singing, bats come out, and, in just a few minutes, the day turns into a kind of twilight.

You have no idea what's going on. It's not nighttime, but it doesn't look like daytime either, and everything has grown dark very quickly. There are no telescopes or mobile apps that can explain what's happening.

It's easy to see why eclipses have been shrouded in myths, superstitions, and legends for centuries. Civilizations around the world interpreted them as divine signs, omens, or warnings. And, although today we fully understand the scientific explanation behind it, watching an eclipse still evokes a mixture of fascination and awe very similar, I imagine, to what our ancestors must have felt.

The solar eclipse that will be visible from Spain on August 12 will be much more than just a natural spectacle. These phenomena help us understand the Sun’s behavior and underscore the importance of missions such as Proba-3, which GMV is participating in by developing essential technologies for studying the solar corona.

On August 12, Spain will be one of the prime locations from which to view a solar eclipse—an exceptional opportunity to enjoy one of nature’s most fascinating spectacles.

Why does a solar eclipse occur?

A solar eclipse occurs when the Moon comes between the Earth and the Sun and casts its shadow over part of our planet. Although the Moon is about 400 times smaller than the Sun, it is also about 400 times closer to us. This extraordinary alignment makes both appear to be nearly the same size in the sky and allows our moon to partially or completely obscure the sun's disk for a few moments.

The shadow cast by the Moon on Earth can be seen very clearly in some photographs taken from the International Space Station. These images offer us a different perspective on the eclipse: from space, the lunar shadow appears as a large dark patch moving across the Earth's surface.

The alignment of the Sun, the Moon, and the Earth occurs only when certain geometric conditions are met. The Moon's orbit is slightly inclined relative to the plane of Earth's orbit around the Sun, so most of the time the three bodies do not align perfectly. An eclipse occurs only when those geometric conditions align.

Behind a phenomenon that seems almost magical are centuries of observations, mathematical models, and scientific advances that allow us to know with great precision when it will occur, how long it will last, and from where it can be observed.

Every eclipse is different. Depending on the alignment's geometry and the vantage point from which it is observed, it can be total, partial, or annular. During a total eclipse, such striking phenomena as the diamond ring or Baily's beads can be observed.

An opportunity to study the Sun

Eclipses are phenomena of great scientific interest. Historically, they have led to fundamental discoveries. One of the best-known examples took place in 1919, when the observation of a solar eclipse made it possible to experimentally verify Albert Einstein's theory of general relativity by measuring the deflection of starlight caused by the Sun's gravity.

Today, eclipses continue to provide an opportunity to study the solar corona, whose behavior remains the subject of intense research.

Proba-3: An Artificial Eclipse in Space

Space missions such as Proba-3, in which GMV has played a crucial role in both the development of onboard systems and ground infrastructure, help expand this knowledge. The mission consists of two satellites (the Coronagraph and the Occulter) that, when flying in formation with millimeter-level precision, enable continuous observation of the solar corona for several hours.

To create this artificial eclipse, both satellites must maintain an extremely precise relative position while flying about 150 meters apart. Getting them to function as a single scientific instrument requires advanced navigation, control, and operation systems, both on board and on Earth. GMV's involvement in these technologies helps make this high-precision formation flight possible.

Today, understanding the Sun's behavior plays a key role in space weather. Solar flares and coronal mass ejections can generate storms capable of affecting satellites, GNSS systems (such as GPS or Galileo), communications links, and even energy infrastructure. Thanks to solar observation missions and monitoring systems, it is now possible to detect these phenomena and take steps to minimize their effects.

Solar observation not only expands scientific knowledge. It also helps us anticipate phenomena that could affect essential services on Earth.

Proba-3 is just one example of how space missions can improve life on Earth. The scientific knowledge they provide can help protect essential services for millions of people.

How to Safely View the Eclipse

• Use only eclipse-approved glasses and make sure they are not damaged. 
• Do not look directly at the Sun or view it through cameras, binoculars, or telescopes without proper filters. 
• Plan your destination and travel arrangements in advance. 
• Follow the instructions of the authorities and comply with access restrictions and fire prevention measures.

When Planning Isn't Enough

In 2024, during the total solar eclipse in Mexico, I had the opportunity to experience a total solar eclipse for the first time. As an astronomy enthusiast (and as an engineer), I had been planning the trip for months. We had studied maps, chosen a location within the path of totality, and checked the weather forecasts.

When the eclipse had reached approximately 70% coverage, the sky became completely overcast. After traveling so many kilometers and putting so much planning into it, we weren't able to see the highlight of the eclipse.

To avoid large crowds, we ended up at a school in a small town in the Torreón region.

There, we waited alongside teachers, families, and students, who welcomed us as if we were part of their community. We showed them the photos taken before the clouds rolled in and talked with the children about space and astronomy.

That experience reminded me of something that is part of any scientific or technological endeavor: no matter how rigorous the planning, there are always variables we cannot control. Preparing, adapting, and sharing knowledge are essential both for observing an eclipse and for carrying out a space mission.

Author: Mariasole Melara