Looking into space

The official name of “TURM Observatory” refers on the one hand to the place where the observatory is set up – “turm” being the German word for “tower” – and on the other is the abbreviation of “TU Darmstadt Remote Observatory”, and with that explains the operating mode. The instruments can be operated remotely and broadcast their images and data to any location. Professor Robert Roth of the Institute of Nuclear Physics has connected his laptop to the observatory and projects live images into the lecture hall. The surface of the sun can be seen in the light of the calcium ions present there, which provides information on the magnetic field activity of the sun and clearly shows which regions are particularly active.

The turbulent motion of the earth's atmosphere known as “seeing” lets the image of the sun waft on the wall of the lecture hall. Earthly clouds float by from time to time, darkening the view. These disturbances are easy to deal with. “We usually record a video and select the best pictures afterwards,” explains Roth. The mount on which the four telescopes sit in parallel automatically locates each desired astronomical object on input, fixates it, and then slowly pans along so that the observation object does not slip out of sight due to the Earth's rotation.

The four telescopes – currently in the summer set-up – have different tasks, two observing the sun in the light of the hydrogen-alpha line and one in the light of the calcium-K line. The fourth depicts astronomical objects in white light, i.e. the entire spectral range visible to the human eye. Observers can draw many conclusions from this.

The emitted calcium line, which comes from a layer just above the sun's photosphere, provides information on e.g. magnetic fields. Images of the hydrogen alpha line reveal spectacular prominences and coronal mass ejections that are thrown from the sun's surface into space. “There can be an extraordinary dynamic behind this,” explains Roth. “Some structures come and go within five minutes.” However, the sun's activity changes periodically, and last year passed a minimum. “There hasn't been much going on yet this summer.”

More spectacular was the partial eclipse in June, which the department streamed for students via Zoom and Twitch, and in doing so made astronomy tangible. Because this is what the observatory is all about: enriching teaching and not only presenting the principles of physics in theory but also “making them tangible through observation”, says Roth.

This idea was the decisive factor for him and his colleague Dr. Franco Laeri of the Institute of Applied Physics in initiating the construction of the observatory as soon as the renovation plans for the Uhrturm became known. Thanks to donations the observatory became reality and has been in operation since 2020. This includes day and night observations, the latter being “the most demanding way to photograph because you have to create sharp images of luminous points,” says Roth – with exposure times of up to many minutes. In winter the focus is on night observations because the sun no longer rises high enough to be visible above the edge of the tower hood. The results are spectacular images of celestial objects, which the department displays on the TURM website.

The location in the middle of the city is not ideal. Light pollution and air turbulence created over heated roofs limit the possibilities for night observations. So the department has set up a second remote-controlled observatory in Extremadura in Spain. Under dark skies with many clear nights, the telescopes there provide fascinating insights into the depths of the universe. The instruments can be used for interactive observations such as the department's “Digital Star Parties”, just like the telescopes on the Uhrturm – even though they are more than 2000 kilometres away. Fully automated operation is also possible. The instruments observe the sky throughout the night and continuously take pictures according to an observation plan developed by the students.

The beautiful pictures are not just a treat for the eye. Behind them is quantitative data from which the students learn to draw scientific conclusions. Periodic variations in the brightness of stars reveal much about the dynamic mechanisms in their interior. Dips in brightness during occultations in binary star systems allow the determination of orbital parameters. Light curves reveal the presence of exoplanets as well as the size and distance from their central star. Lines in a star's spectrogram show what chemical elements are present on its surface. “These observations are conducted in lectures or student lab courses, but they are also already close to being research,” says Roth. “Our light curves of exoplanets can be used, for instance, to prepare future research missions.” Students can use the recorded images and data, operate the observatory themselves and incorporate it in their work. “Many of the students are absolutely fascinated by all this,” says Roth.

The Department of Physics has a strong programme in research and teaching in the fields of theoretical and nuclear astrophysics. According to Roth, there has yet been a lack of activities in observational astrophysics and astronomy. “We're filling this gap with the TURM Observatory.”