VUB researchers measure light, colour and temperature during a unique eclipse flight

BRUSSELS, 13 August 2026 – What exactly happens to the light around us when the Sun is 96 per cent obscured by the Moon? And what role does the atmosphere play in the changes we observe during a solar eclipse? VUB researchers investigated this during Brussels Airlines’ special eclipse flight, during which they precisely mapped light intensity, light colour and temperature. The measurements were combined with observations carried out on the ground in Spain by a team of astronomers led by VUB Professor Katrien Kolenberg. This enabled the researchers to study the same eclipse from two different positions in the atmosphere.

For VUB Professor Valéry Ann Jacobs, who researches the impact of light on people and the environment, the eclipse flight was, first and foremost, a unique natural experiment. “In a sense, a solar eclipse is the opposite of how we normally work. Instead of taking measurements in a small, dark laboratory, for one evening the universe was our laboratory. In a very short space of time, nature removes a large proportion of its most important light source. This gives us the opportunity to investigate very precisely what happens to our environment when that light source suddenly diminishes significantly.”

How much light remains during a 96 per cent eclipse?

During the flight, the researchers collected time series of light intensity and carried out spectral measurements to determine the colour of the ambient light as well. After all, an eclipse percentage does not directly indicate how much light remains in the environment. The sun is partially obscured, but the light we perceive is also scattered and reflected by the atmosphere, clouds, the landscape and buildings.

“We do not experience an eclipse as a percentage of the sky. We experience it as a change in the brightness and colour of the world around us. It is precisely this change that we aim to objectify with our measurements,” says Valéry Ann Jacobs.

Particular attention is being paid to the blue-green glow that observers sometimes describe during the total phase of an eclipse. Both physical processes in the atmosphere and changes in human colour perception may play a role in this. By comparing the spectral measurements taken from the aeroplane with those taken on the ground, the researchers hope to better determine which part of the effect is caused by the light itself and what role the atmosphere and human perception play.

Unique comparison between air and ground

The scientific team deliberately opted for a combination of measurements taken from the air and from the ground. At flying altitude, a large part of the atmosphere lies below the researchers, whilst observers on the ground view the eclipse through the entire atmospheric column.

“The same eclipse, the same Sun and the same Moon, but observed from two very different positions within our atmosphere. That makes these measurements particularly interesting,” says Katrien Kolenberg.

Temperature was also monitored during the flight. On the ground, an eclipse can lead to a noticeable drop in temperature because the Earth’s surface temporarily receives less solar radiation. During the flight, the researchers did not initially observe any clear drop in temperature at high altitude. This is consistent with the hypothesis that the typical temperature effect of an eclipse manifests itself mainly close to the Earth’s surface. The researchers emphasise that the full set of measurement data has yet to be analysed.

An aeroplane as a scientific laboratory

The eclipse flight not only offered an exceptional vantage point for observation but also presented a methodological challenge. After all, a passenger aeroplane is not a laboratory: equipment must comply with strict safety requirements, whilst the aeroplane is constantly moving and changing its course and angle of inclination. The researchers installed measuring equipment and cameras on both sides of the aeroplane and will need to link the data retrospectively to the aircraft’s exact position, heading and movement.

“A key outcome of this experiment may not be a single spectacular figure, but a better method for future observations. We now have a much clearer understanding of the technical challenges involved and how we can tackle them during the next eclipse,” says Valéry Ann Jacobs.

Research continuing after the eclipse

The eclipse flight therefore marked not the end, but the beginning of a new research process. The two VUB students who took part in the experiment will continue to analyse the collected data over the coming months. In addition, they will examine how the data gathered from the air can be linked to measurements taken by other research teams.

Based on this, the researchers aim, amongst other things, to gain a better understanding of how light intensity, the light spectrum and temperature change during an eclipse, and what role the atmosphere plays in this. Furthermore, the experience gained from this flight should lead to an improved measurement procedure for future eclipses, including automated time series and more accurate recording of the direction of measurement.

“Science isn’t just about finding answers. This experiment has also raised new questions and taught us how to carry out the next measurement more effectively. That is precisely how scientific research progresses,” concludes Valéry Ann Jacobs.