What if we turned the lights
off so we could look at the
stars together again?

Share article
Ewine van Dishoeck

Professor Molecular Astrophysics

Leiden University
“Just turning that off and being able to see the wonders of the night sky is something that every human should be able to experience.”

December 22nd 2022. Author: Sophie Zimmerman.

Header picture: Shot by Dirk van Egmond. ‘Daan Roosegaarde in the Old Observatory in Leiden’

On September 25th, the lights were turned off across the centre of Leiden and into the neighbourhoods. That night, it wasn’t only the streetlights that flicked off after 10 PM. Many living rooms, business premises, and shop windows also went dark. The reason? To see the starry sky again. This imaginative art project, Seeing Stars Leiden, marked the start of The Space Week, a new initiative that took place as part of Leiden European City of Science 2022.

Looking through a telescope together at the Old Observatory during Seeing Stars
Photo credits: Luis Calcada

When designing the year-long European City of Science festival, it was decided that major themes should be clustered throughout the programme. As a result, the Life Sciences were the centre of attention for a week during spring. In the autumn, it was the turn of the stars, with ten days focused on the theme of Space. During this period, the 365-day calendar of Leiden2022 was full of intriguing daily topics such as Didymos, Space Invaders, Time, and Oumuamua. On September 25th, the topic of the day was 'Shooting Stars.’ That evening, astronomers, astronomy students, and amateur stargazers stood ready with large telescopes throughout the dark city so that residents and visitors could all look at the stars — whether shooting past or suspended in the sky. The darkened streets surrounding the Old Observatory in Leiden were filled with people. Because of mixed cloud cover, fewer stars were visible than hoped, but the experience was nonetheless a special one for the thousands of people who turned out. Fortunately, the clouds cleared just in time for everyone to admire the planet Jupiter, which was at its closest to the earth in almost 60 years and thus became part of the magic.

Light pollution

It's a fact: in our modern world full of light pollution, more than 80 percent of the world's population can no longer experience a starry sky at all. Seeing Stars Leiden shone a light on this issue in a powerful way. As Kathleen Ferrier, president of UNESCO Netherlands, says: "Everyone should have the right to see the stars in a non-polluted night sky. Looking at the stars makes you feel connected to each other. We are, after all, part of the same cosmos.

This is the common and universal legacy that I strive for. Seeing Stars is an important step forward." Artist Daan Roosegaarde — the initiator of Seeing Stars — also wanted to bring back a universal sense of togetherness: “Everyone is in their own bubble nowadays, no longer connected to others, while a great light show takes place every night above all our heads. Seeing Stars brings the stars back to the streets.”

The Old Observatory surrounded by stars.

Photo credits: Ossip van Duivenbode, Studio Roosegaarde

Stargazers with big telescopes were located throughout the city. Everybody could

take a look at the sky - Photo credits: Studio Roosegaarde

Lights out, stars on

Making the starry sky visible that evening in Leiden took quite some work, says director Martijn Bulthuis of Leiden & Partners, the event organiser. “It was initially difficult to convince the city council, mainly because of the potential security risks. One big concern was, what if someone drives into the canal? Or what if burglars see their chance and take advantage of an unlit city?” Turning off all the lights in the area also proved challenging. It turns out there were quite a few lights that nobody knew how to turn off, and dozens of switch boxes had to be checked with the help of energy suppliers and the municipality.

According to Bulthuis, once the lights in the area finally went out that evening, after an intensive preparation process, "a magical atmosphere" was created. “Many inner-city residents came out of their homes to walk through the dark streets. Something really special happened. People started whispering. There was a feeling that you don't usually find in the city. The feeling of: we belong together and are experiencing something together.”

Now that the project is over, the organisers remember that special feeling in the city the most. “There was also the realisation that we have an awful lot of light pollution. That idea has really penetrated and is now being discussed, even within the town hall. Now, serious consideration is being given to turning off the lights on monuments and festive lighting after a certain time,” says Bulthuis.

The Rapenburg in Leiden with and without light pollution - Photo credits: Studio Roosegaarde

Connecting citizensand science

The Seeing Stars project also resonates within Leiden University, says Margaret Gold, coordinator of the Citizen Science Lab Leiden. “We invited city residents to participate in light pollution research through special apps that we developed. In the end, more than 400 measurements were taken that evening by residents and visitors on the streets, simply by using their smartphones,” she explains. “The project was a great success for citizen science.

This was also just the beginning; the discussion about light pollution in the city also lives on among residents. There were so many responses that night. People really want to see things change.” This is music to the ears of the organisers of Leiden European City of Science 2022. Their mission is to connect science and society in a playful, bottom-up way, and the citizen science project of Seeing Stars Leiden has definitely succeeded in doing this.

The Space Week

This spectacular star show also kicked off the first edition of The Space Week: a series of open days and events in the region of Leiden, which is home to 80 percent of Dutch space travel and astronomy. On the day of Seeing Stars, everyone in Leiden with a curious mind got their money's worth. Doors that are normally kept closed were opened. For example, the Old Observatory of Leiden — the oldest existing university observatory — opened itself and its historic telescopes to the public. It was here, in the building’s basement, that The More-than-Planet exhibition focused on the question of how scientists study our planet through Earth observations. Visitors could view the work of five contemporary artists who had portrayed their vision and perspective of this process.

Elsewhere in the city, people could attend the Netherlands Institute for Space Research (SRON) open day. This was an extra special experience as the national institute was not expected to open until later in 2022. The James Webb telescope, which became fully operational earlier this year, was featured here as well as in the Old Observatory, along with its first images that were released in July. The razor-sharp, detailed images have sparked yet another revolution in astronomy.

After a week full of meetings for space professionals and various public activities, the 10-day space extravaganza concluded with a two-day spectacle in Noordwijk. On Saturday, ESTEC — the largest research centre of the European Space Agency — held an exclusive open day for people with disabilities. On Sunday, the NL Space Campus and ESA pulled out all the stops. For the thousands of visitors who managed to get their hands on a free ticket in time, the entire campus was transformed into a festival site. The festival boasted everything from meet-and-greets with ESA astronauts to live music on the ‘Space Rocks’ stage. The entire spectrum of space research and technology was covered — and the audience loved it.

Here to stay, The Space Week is yet another example of a large-scale event created specifically for Leiden European City of Science 2022. The intention to organise The Space Week every year from now on clearly shows its impact. As Torben Henriksen, Director of ESA ESTEC, says: “The Space Week was incredibly dynamic and the perfect opportunity for those of us working with space daily to showcase to the public what we do in space, what space is, how space is an integral part of our daily life, and how it’s an integral part of everybody’s daily life. We’re passionate about space. We want to show and demystify it.’

“The project was a great success for citizen science. This was also just the beginning; the discussion about light pollution in the city also lives on among residents. There were so many responses that night. People really want to see things change.”

Margaret Gold, Citizen Science Lab Coordinator at Leiden University

Leiden2022 European City of Science

Leiden European City of Science 2022 is a 365-day science festival packed with activities, lectures, workshops, excursions, exhibitions, and events, for anyone with a curious mind, the goal of which is to connect science and society.

For more information contact Leiden&partners at or +31 71 516 600.
Leiden2022 is an initiative of the Municipality of Leiden, Leiden University, Leiden University Medical Center and the Leiden University of Applied Sciences, supported by the European Commission and many local, national and international partners.