Frankfurt Physicists Explore the Night Sky at the Nordic Optical Telescope
Perched on the slopes of Roque de los Muchachos, the Nordic Optical Telescope (NOT) stands 2,400 meters above sea level. Accessible only via a narrow, winding road and surrounded by black volcanic rock and sparse vegetation, the observatory is about a 40-minute drive from the nearest town. It’s a remote location, but there is no place else the two young scientists Annika Schichtel and Clara Peter would want to be. For months, the physicists from Professor Camilla Juul Hansen’s research group at Goethe University Frankfurt had eagerly anticipated this research trip to study the night sky. Three other colleagues also joined. La Palma offers exceptionally dark skies, thanks to a 1988 law protecting against light pollution – the first of its kind globally. Combined with minimal atmospheric disturbances at this altitude, the observing conditions are ideal.
Challenges in Measurement
“One of NOT’s unique aspects is that we were able to conduct all the measurements ourselves,” Peter explains. Unlike many observatories where staff handle the instruments, here, researchers are responsible for setting up and operating the equipment, verifying coordinates, and essentially turning night into day. What began as a well-planned expedition with three nights of observation quickly turned into a minor adventure. After the first night, during which two support astronomers provided a comprehensive introduction, unforeseen circumstances changed the plans: two colleagues had to leave the station due to illness. “Suddenly, it was just us,” Schichtel recalls with a laugh. “Fortunately, this was my second time here.”
“We were a dream team,” both affirm – and fortunately so, because the second night brought yet another surprise. A “Target of Opportunity” request arrived, i.e. an urgent observation proposal from external scientists that the astronomers have to execute on-site. The observation schedule was swiftly adjusted, and Schichtel and Peter’s own measurements postponed. “It was quite stressful. We had already encountered difficulties setting up our guide star, and then this happened,” Peter recalls.
A Window into the Universe
Despite the challenges, there was ample time for their own research. A typical workday for the astronomers began around 4 p.m. with preparations. “We open all the dome’s shutters and start calibrating the instruments,” Peter explains. “We need some daylight for that.” Once the sun sets, the actual measurements commence. Following a precise schedule, the telescope is directed to the desired star at the appropriate time. Each exposure lasts about 30 minutes and is often repeated multiple times to ensure reliable results. The protective dome rotates in sync with the telescope to maintain an unobstructed view. To counteract Earth’s rotation and keep the image stable, the telescope continuously adjusts its position. This work continues until 7 a.m., when the approaching daylight ends the observations.
Between Carbon and Thorium
For her doctoral research, which began in late 2024, Schichtel studies carbon-enhanced metal-poor stars – also known as CEMP stars. These stars exhibit unusually high carbon levels and low metal content, making them valuable cosmic time capsules that offer insights into the formation of chemical elements in the early universe. Peter’s master’s thesis focuses on determining the ages of particularly old stars using thorium. With a half-life of about 14 billion years, this radioactive heavy metal serves as a cosmic clock.
Both scientists employ spectral analysis in their research, breaking down starlight into its individual wavelengths. “Each element leaves a unique signature in the spectrum, much like a fingerprint,” Schichtel explains. This method allows them to determine the chemical composition of distant celestial bodies and draw conclusions about their origin and evolution.
A Change in Perspective
At the end of their stay, the physicists hiked to the summit of Roque de los Muchachos. From there, they enjoyed a breath-taking view of the volcanic island and the sea. Particularly mesmerizing was the natural phenomenon known as the “cloud waterfall”, where the cloud cover flows over the mountain ridge like a massive waterfall. “Spectacular,” they both agreed – a word that aptly describes their entire research journey.
