The Effelsberg radio telescope turns 50
On the occasion of the anniversary, the Time Travel Trail is opened as the fourth astronomical hiking trail at the radio telescope
The 100-m radio telescope of the Max Planck Institute for Radio Astronomy in Bonn celebrates its 50th birthday in 2021. The construction of the telescope in an Eifel valley about 40 km southwest of Bonn took place in three and a half years from 1967 to 1971. On May 12, 1971, an official opening was celebrated at the site of the telescope, close to the two Eifel villages of Effelsberg and Lethert, which are now districts of the town of Bad Münstereifel.
To mark the anniversary, a fourth astronomical hiking trail, the Time Travel Trail, has been completed in May 2021. It has a total length of 5 km around the 100-m radio telescope, presenting the 50-year history of the Effelsberg radio telescope on 20 panels. The panels inform about scientific results with the telescope, as well as remarkable technical innovations such as the installation of a new subreflector or the construction of the LOFAR station Effelsberg for radio observations at longer wavelengths.
The 100-m radio telescope of the Max Planck Institute for Radio Astronomy is located in a stream valley directly on the border between the German states of North Rhine-Westphalia and Rhineland-Palatinate. From the visitor parking lot near the Eifel villages of Effelsberg and Lethert, both parts of the local municipality of Bad Münstereifel, it is about a 15-minute walk to the radio telescope's visitors’ pavilion with a direct view of the telescope itself.
As a retrospective of 50 years of successful research work with the Effelsberg 100-m radio telescope, a new hiking trail, the "Time Travel Trail," has been opened in May 2021 in the neighborhood of the Effelsberg radio telescope. It starts at the visitors’ pavilion in the immediate vicinity of the 100-m radio telescope, leads around the telescope on a route of just over 5 km and ends at the lookout point directly in front of the giant antenna. From there, a short zigzag path leads directly back to the pavilion.
"The new hiking trail not only presents a fascinating insight into 50 years of research and technology in Effelsberg, but also allows a view of the spectacular telescope and the surrounding beautiful Eifel landscape from different perspectives," says Alex Kraus, the station manager of the Effelsberg Radio Observatory. "Already during my PhD at the institute, I had a lot of observing time with the telescope to study the short-term variability of active galactic nuclei." This topic is documented in Station No. 8 of the Time Travel Trail.
The Time Travel Trail describes in a total of 20 stations a series of events from five decades of history of the 100-m radio telescope, from its inauguration in 1971 to the 50th anniversary in the current year 2021.
These include both scientific and technical milestones, from the first discovery of the molecules water and ammonia outside the boundaries of our Milky Way in 1977/79 to the world record angular resolution of only 11 microarcseconds (equivalent to the diameter of a 1-cent coin on the surface of the Moon) by Space VLBI observations with the 100-m telescope. In addition, there are technical milestones such as the installation of a new subreflector with adjustable surface in 2006 and the commissioning of a second radio telescope on site, the Effelsberg station of the European LOFAR telescope network.
The Time Travel Trail runs around the site of the radio observatory, in the area of not one but two German states (North Rhine-Westphalia and Rhineland-Palatinate).
This hiking trail, marked by a black telescope symbol on a yellow background, was established in a cooperation of the Max Planck Institute for Radio Astronomy with the “Freundeskreis Sahrbachtal”, the “Tourist-Information/Stadt Bad Münstereifel” and the OG Bad Münstereifel of the Eifelverein. It complements the three already existing astronomical trails, Planet Trail, Milky Way Trail and Galaxy Trail, which depict almost the entire cosmic distance scale from our solar system to the most distant galaxies at distances of billions of light years.
“The Eifelverein Bad Münstereifel congratulates the Effelsberg radio telescope on its 50th birthday and is proud to have now implemented another attractive and informative hiking trail, in collaboration with the other cooperation partners, and in addition to the two already existing “Eifelschleifen” from Bad Münstereifel to the telescope and around Effelsberg," says Bernhard Ohlert, chairman of the OG Bad Münstereifel of the Eifelverein.
"The Freundeskreis Sahrbachtal e.V. sends congratulations on the 50th anniversary of the Effelsberg radio telescope, which is masterfully embedded in the natural environment of the Ahr Mountains. With this constantly improved scientific instrument important results in astronomical research could be obtained", adds Walter Brüggemann, the chairman of the Freundeskreis. "The Freundeskreis welcomes the opening of the new Time Travel Trail as an offer for further information and knowledge to interested hikers. We look forward to the continuation of our "historically grown" good cooperation with the MPIfR and thank for the excellent cooperation as well as the impact on tourism."
"With the Time Travel Trail, we have an attractive ensemble of astronomical hiking trails at the Effelsberg radio telescope," concludes Norbert Junkes, the press officer of the Max Planck Institute for Radio Astronomy, to whom the conception of the four hiking trails goes back. "In the future, we would like to further expand the system of virtual connecting stations between our trails, which already makes the Planetary Trail with the "Sirius" station at the APEX telescope in Chile the longest astronomical trail on Earth."
In the following, a short description of all 20 stations of the Time Travel Trail (see also table in Figure 3) is given:
1. The first station of the trail represents the inauguration of the radio telescope after about three years of construction on May 12, 1971. Already on April 23, the supernova remnant HB21 was observed as the first successful measurement ("First Light") with the Effelsberg radio telescope.
2. Station no. 2 marks the start of full operations for the Effelsberg radio telescope and its receiver systems on August 01, 1972. In the same year, first pulsar measurements were made at a wavelength of 2.8 cm, which was the shortest wavelength used for pulsar observations to this time.
3. In 1973, the Effelsberg radio telescope was integrated into a worldwide network of radio telescopes ("Very Long Baseline Interferometry", VLBI), already at a very early stage of its operation. The first measurements with transatlantic baselines took place, enabled by the connection of the 100-m telescope with radio telescopes in the U.S.
4. One year later, in 1974, the Effelsberg radio telescope was used as a receiving station for the HELIOS solar probe for six months during daytime. HELIOS was the first major project of German spaceflight. In the same year, the first complete map of the radio emission of the Andromeda galaxy M31 at 11 cm wavelength was published.
5. Due to its high sensitivity, the Effelsberg radio telescope is ideally suited for measurements of extremely weak radio signals. Though, spectral lines of water H2O (1977 in M33) and ammonia NH3 (1979 in IC342) could be detected for the first time in other galaxies several million light-years away.
6. After about ten years of measurements with the three largest fully steerable radio telescopes on earth at that time (Effelsberg: 100-m, Jodrell Bank: 76 m, Parkes: 64 m diameter), the most accurate map of the radio emission of the complete sky at 73 cm wavelength was published in 1982.
7. Observations of a whole range of spectroscopic lines of the ammonia molecule NH3 with the Effelsberg radio telescope led to the introduction of a cosmic thermometer to derive the temperature of molecular clouds.
8. The Effelsberg radio telescope was essential for the discovery of short-term variability in the cores of extragalactic radio sources. In the central regions of extremely distant active galaxies (e.g. 0917+624, nine billion light-years away), one finds brightness variations within a few hours and can thus detect structures as small as the size of our solar system.
9. The Zeeman effect is the splitting of spectral lines in magnetic fields (Nobel Prize for Pieter Zeeman 1902). The verification of this effect in space was first demonstrated with the radio telescope Effelsberg for the water molecule H2O. This enables the investigation of magnetic fields in molecular clouds.
10. A circular rail of 64 m diameter carries the complete weight of the Effelsberg radio telescope. After 25 years of operation, this rail had to be completely replaced. For this purpose, the telescope with its total weight of 3200 tons had to be "jacked up" for the time of the rail replacement.
11. Einstein's general theory of relativity predicts a continuous change in the direction of a pulsar's rotation axis (geodetic precession) when it moves in the gravitational field of a companion star. With the Effelsberg radio telescope, this effect could be proven for the first time in case of the pulsar PSR 1913+16.
12. The systematic study of the magnetic fields of galaxies and of our Milky Way was started by observations of polarized radio emission with the Effelsberg radio telescope. A nice example is presented in a detailed map to study the magnetic field of our neighbour galaxy M31 at 6 cm wavelength.
13. The subreflector of the Effelsberg radio telescope with a diameter of 6.50 m is located near the focal point at the tip of the four support legs. On October 5, 2006, a new, improved mirror with 100 motor-controlled active surface elements was installed, further increasing the performance of the radio telescope.
14. The first German station of the European low-frequency radio telescope LOFAR was built at the site of the Effelsberg Radio Observatory. LOFAR stations are distributed over several countries in Europe and are directly connected via fast data line connections.
15. Special measurement programs to find new pulsars are running at the Effelsberg radio telescope. PSR J1745+10 is the first millisecond pulsar discovered at Effelsberg. It is a so-called "black widow pulsar", where the pulsar's high-energy radiation is almost completely vaporizing its partner over time.
16. A pulsar with an extremely strong magnetic field, a so-called magnetar, was detected with the Effelsberg radio telescope in the immediate vicinity of the center of the Milky Way. It moves in an orbital period of about 500 years around the supermassive black hole in the centre (Sgr A* with more than 4 million solar masses).
17. Within the project "Effelsberg-Bonn-HI-Survey" (EBHIS), the complete northern sky was observed in the light of the 21-cm spectral line of neutral hydrogen (HI) with the radio telescope Effelsberg.
18. Studying the spectral lines of water masers in the galaxy NGC 4258 in a Space-VLBI network connecting the RadioAstron space telescope with a number of Earth-based radio telescopes including the 100-m telescope, the highest angular resolution in astronomy with 11 microarcseconds only could be achieved.
19. The "Global Millimeter VLBI Array" (GMVA) is used to investigate details within the central regions of galaxies like Perseus A, Cygnus A, M87 and Sgr A* (center of the Milky Way) at very high angular resolution. At a wavelength of 3.5 mm only, the partizipating 100-m radio Effelsberg is pushed to its limits.
20. In 2021, the Effelsberg radio telescope has completed the first 50 years of its life. To mark the occasion, the German postal service issued an anniversary stamp “50 Jahre 100-m-Radioteleskop Effelsberg”. Observations and research programs with the 100-m telescope will be continued.
The Time Travel Trail at the Effelsberg radio telescope complements the three existing astronomical trails around the radio observatory, Planet Trail, Milky Way Trail and Galaxy Trail, which include the complete astronomical distance scale from our solar system to the most distant galaxies billions of light years away.