Lichtgedanken 04

S C HW E R P U N K T 34 the service of science. There is no better way to spend a clear night, responds Mugrauer with emphasis and a smile, before beginning to enthuse about the conditions for observing the night sky in Chile, where he lives from time to time and has spent the past weeks. »No clouds, no mist, from sunrise to sunset. We only get that for a handful of nights per year here.« That is why it is so im- portant to make the most of them. This passion for the stars, combined with the various technologies used to observe them, can be felt in almost every sentence Mugrauer utters. He be- gan watching the stars back in primary school; back then in the public observa­ tory in his home town of Munich. That was 32 years ago—»not long ago in the cosmic dimensions.« While his colleague prepares the ob- servations in the control room, Markus Mugrauer takes me inside the dome— the centrepiece of the Observatory— in which the 90-centimetre reflector telescope stands: five metres tall and weighing 13 tonnes. Mugrauer presses a button to move the dome into posi- tion, and then the roof opens immedi- ately afterwards, with a loud rumbling. There is now hardly any light coming from outside; evening birdsong is the only thing to penetrate the air. Mugrauer climbs an aluminium lad- der and removes the large metal cover, which encloses the tube of the telescope to protect it from dust and insects. »We operate three telescopes on one mounting«, he explains. Two smaller telescopes sit next to the large 90-cen- timetre reflector: a reflector telescope with a 25-centimetre diameter—a so- called Cassegrain telescope—and a re- fracting telescope with a 20-centimetre diameter. The University telescope can even be controlled from Hawaii The University Observatory has been operating in Großschwabhausen for 56 years now, and the telescope and its mirror are still in their original condi- tion following the »first light« in 1962. »Only the drive motors have been re- placed«, explains Mugrauer. Back in the 1960s, researchers controlled the telescope using a control desk meas- uring just under two metres in width and located in the dome. Nowadays, it is controlled from the heated control room, located on the floor below. »Or from Hawaii«, jokes Mugrauer. In the- ory, the University telescope could be controlled from anywhere on earth. However, in this moment, we go down the stairs with the help of torchlight. The control room is the only lit part of the Observatory; light in any other part of the building would interfere with the observations. There is coffee. Mugrauer takes his seat, several computers hum, four monitors sit side-by-side. Susanne Hoffmann has already started several calibration measurements. But for now, the screens are just displaying lots of controls and coordinates and making dull white noise. »We start by taking various comparative images«, explains the astrophysicist. Thus, the homogeneous grey surface of the sky is captured at dusk so the various sen­ sitivities of the CCD detectors used can be corrected. The recorded dark imag- es also register the individual signals of the light-sensitive CCD detectors, which need to be taken into account when processing the data. At the same time, Mugrauer calibrates the échelle spectrograph. The telescope is currently being operated in Nasmyth Night shift under a starry sky The University’s Observatory is situated in a section of forest near Großschwabhausen, shielded from the night lights of Jena City of Light. Exoplanets, young star clusters, double stars and gigantic black holes are all observed here on almost every clear night. Astrophysicists Markus Mugrauer and Susanne Hoffmann gave our reporter a look behind the scenes and the chance to admire the sky through the reflector telescope. Find out what she discovered in this article. BY UTE SCHÖNFELDER It is a warm spring evening, shortly af- ter Easter. It is around seven o’clock at night and the sun still glistens on the horizon, as I travel due west from Jena. I pass Remderoda and, after around ten kilometres, arrive in Großschwabhaus- en. The small villages are quiet and secluded on a slight hill; the sky seems closer than it does in the valley basin of Jena. A rural idyll, fresh air, peace and quiet. I check the directions provided on the Observatory’s website to remind my- self: there should be a track leading off from the main road towards the Ob- servatory. Despite this, my sat nav just shows a green space. Feeling slightly uneasy, I turn left and follow a track that is barely three metres in width, directly into the forest, lined on each side by a dense forest of tall trees. After around three hundred metres: relief. Between the treetops, with the sun set- ting in the distance, I discover the dome of the round, yellow-painted building, which stands in a small clearing. The astrophysicists begin their work in the »blue hour« A precisely cut hedge directs you to the entrance. Dr Markus Mugrauer wel- comes me into the building. He will spend the night watching the sky to- gether with his colleague Dr Susanne Hoffmann. For the astrophysicists, their working day begins at dusk, in the »blue hour«. »Depending on the weather, we can observe the sky from here for around 120 nights each year«, says Mugrauer. He is planning on mak- ing the most of the predicted period of good weather over the next three days. It is Friday evening, I say, a weekend in F E AT U R E