Complementing two earlier astronomical trails at the Effelsberg radio telescope, labelled Planetary Trail and Milky Way Trail, we have built a third trail, called Galaxy Trail in order to extend the cosmic distance scale to the edge of the Universe. The Galaxy Trail comprises a total of 14 stations leading from our Milky Way Galaxy along its neighbour, the Andromeda Galaxy (M 31), to extremely distant objects like the galaxy SDSS J1148+5251. Its emission takes almost 13 billion years before reaching our telescopes. The Galaxy Trail starts east of the 100 m radio telescope in the forest and leads to a nearby hut (“Martinshütte”) which is reached after 2.6 km distance including a steep climb through the forest.
The Galaxy Trail was built as a cooperative project between the Max Planck Institute for Radio Astronomy and the Freundeskreis Sahrbachtal. The logo for the Galaxy Trail is a blue telescope on white background:
Here a link with trekking information on the Galaxy Trail:
The information presented on the 14 stations of the Galaxy Trail is compiled in the following.
The Galaxy Trail at the Effelsberg Radio Observatory runs from the 100 m radio telescope to the Martinshütte, a small hut belonging to the nearby Kirchsahr municipality. The walk is scaled 1 : 5 x 1022 (1 : 50 sextillions) meaning 5 billion light years per kilometre or a million light years per 20 centimetres. Our home galaxy, the Milky Way, is only at a distance of 50 centimetres from its large neighbour, the Andromeda galaxy, corresponding to a real distance of 2.5 million light years.
On a total length of about 2.6 kilometres (exactly 2570 metres) there are 14 stations describing a journey from our position in the Milky Way to sources at the edge of the known universe, their radiation reaching us over a light travel time of more than 13 billion years.
1) Milky Way
The starting point of the Galaxy Trail is our Milky Way. Our home galaxy consists of far more than a 100 billion stars, forming a flat spiral of 100,000 light years in diameter.
From here it takes 12.85 billion light years (scaled: 2,570 m) to the final destination at the edge of the known Universe. At normal walking speed (3 km/h – because of a bit of ascent on the walk) it takes a bit less than an hour, walking at 100 trillion times the speed of light in scale.
2) Andromeda Galaxy M 31
The Andromeda-Galaxie (M 31) is our next large-scale neighbour, a galaxy even larger and more massive than the Milky Way. At a clear night sky, far away from the city lights it might be visible to the unaided eye.
From the start we have walked 2.5 million light years (or 50 cm) and it takes another 12.85 billion light years (2570 m) to the final destination.
3) Starburst Galaxy M 82
The Starburst Galaxy M 82 (NGC 3034) in the constellation Ursa Major (the great bear) is interacting with its large-scale neighbouring galaxy M81 and thus showing a strong burst of star formation in its central area.
From the start we have walked 12 million light years (or 2.4 m) and it takes another 12.84 billion light years (2568 m) to the final destination.
4) Active Galaxy M 87
The active galaxy M87 (also NGC 4486, or Virgo A) is the central galaxy of a large cluster of galaxies, the Virgo cluster in the direction of the constellation Virgo (the virgin). M87 is a giant elliptical galaxy, 10 times more massive than the Milky Way, with a central black hole of several billion solar masses.
From the start we have walked 50 million light years (or 10 m) and it takes another 12.8 billion light years (2560 m) to the final destination.
5) Active Galaxy NGC 1275
The active galaxy NGC 1275 (also Perseus A or 3C 84) is the central object of another cluster of galaxies, the Perseus cluster in the direction of the constellation Perseus (the Greek mythological hero). It is 100 times further away than the Andromeda galaxy.
From the start we have walked 250 million light years (or 50 m) and it takes another 12.6 billion light years (2520 m) to the final destination.
6) Cygnus A
The radio galaxy Cygnus A (3C 405) is one of the strongest radio sources in the sky. It is in the direction of the constellation Cygnus (the swan). Radio images at higher resolution show a central nucleus with two energetic jets blowing out two radio lobes.
From the start we have walked 750 million light years (or 150 m) and it takes another 12.1 billion light years (2420 m) to the final destination.
7) Quasar 3C 273
The quasar 3C 273 lies in the direction of the constellation Virgo (the virgin) and is the brightest “quasi-stellar source" or quasar in the sky. With an apparent magnitude of 13 it is as bright as the dwarf planet Pluto, but much more distant. Its total brightness is 300 times that of our Milky Way.
From the start we have walked 2.2 billion light years (or 450 m) and it takes another 10.65 billion light years (2120 m) to the final destination.
8) Quasar 3C 48
3C 48 in the direction of the constellation Triangulum (the triangle) is also a quasar. It is actually the first observed quasar, identified in the year 1960. The redshift of its spectral lines is 0.367, corresponding to a light travel time of almost four billion years.
From the start we have walked 4.0 billion light years (or 800 m) and it takes another 8.85 billion light years (1770 m) to the final destination.
9) Quasar 3C 295
3C 295, in the direction of the constellation Boötes (the herdsman) is also a quasar, a radio galaxy with an extraordinarily bright nucleus. The source is regularly used as a calibration source for observations with the Effelsberg radio telescope in order to gauge the position accuracy (pointing) as well as the signal strength (flux calibration).
From the start we have walked 4.75 billion light years (or 950 m) and it takes another 8.1 billion light years (1620 m) to the final destination.
For galaxy B0218+367 in the direction of the constellation Triangulum (the triangle) it was possible to proof that a fundamental constant, namely the proton-electron mass ratio, is valid not only in the local but also in the distant universe.
From the start we have walked 6 billion light years (or 1200 m) and it takes another 6.85 billion light years (1370 m) to the final destination.
11) Quasar 3C 286
The quasar 3C 286 is observed in the direction of the constellation Canes Venatici (the hunting dogs). It is one of the most important calibration sources for radio observations with the Effelsberg 100 m radio telescope.
From the start we have walked 7.1 billion light years (or 1420 m) and it takes another 5.75 billion light years (1150 m) to the final destination.
The radio source 0917+62 is in the direction of the constellation Ursa Major (the great bear). The source is the nucleus of a distant radio galaxy. Brightness fluctuations on a very short time scale (so-called “Intraday Variability“ or IDV) were detected with the Effelsberg radio telescope.
From the start we have walked 9.2 billion light years (or 1840 m) and it takes another 3.65 billion light years (730 m) to the final destination.
13) MG J0414+0534
In 2008, the water molecule (H2O) was detected with the Effelsberg 100 m radio telescope in the galaxy MG J0414+0534 in the direction of the constellation Taurus (the bull) in a record distance of more than 11 billion light years.
From the start we have walked 11.3 billion light years (or 2260 m) and it takes another 1.55 billion light years (310 m) to the final destination.
With the galaxy J1148+5251 in the direction of the constellation Ursa Major (the great bear) we have reached the last target of our Galaxy Trail. The radio signal takes almost 13 billion years in order to reach the Earth and it is still possible to trace gas and dust in this distant galaxy.
From the start we have walked 12.85 billion light years (or 2570 m) and (almost) reached our final destination. After another 950 million light years (or only 200 m) we would be coming back to the Big Bang and the beginning of our Universe. That position is marked by the Martinshütte (the “hut at the edge of the Universe”).
1) Redshift and Distance
The huge distances of the target stations of the Galaxy Trail implied that the distances starting at a few hundred million light years (e.g. Perseus A) were derived from the observed redshifts in the spectral lines of these objects. The first identifications of quasars as highly redshifted objects were proven for a station of our Galaxy Trail (3C 273) already in 1963. Almost all distance values for the targets of the Galaxy Trail have been derived that way. At very high redshift values, relativistic effects and cosmological models must be taken into account. Because of the complex structure of the Universe, there is no distinct distance value any more. For the stations of the Galaxy Trail we have derived “light travel distances" applying standard values in the cosmological model with Ned Wright‘s “Cosmology Calculator“ available in the internet. We define that a galaxy with a light travel time of 10 billion years is in a distance of 10 billion light years. Thus the (observational) edge of the Universe is defined by its age. Pushing the record with higher and higher observed redshift values leads further back in the history of the Universe approaching the moment of its creation approximately 13.8 billion years ago (this value taken from the analysis of the cosmic microwave background with the European Planck satellite).
A concise compilation of methods for cosmic distance calculations is provided in the following chapter in Richard Pogge‘s lecture series at Ohio State University: The Cosmic Distance Problem (Lecture 22).
2) Calibration sources for the 100 m Radio Telescope
The targets of the Effelsberg Galaxy Trail include a number of standard calibration sources in the sky which are used to calibrate radio astronomical observations with the 100 m radio telescope. Calibration observations come in three different flavours: 1) positional accuracy (pointing observations); 2) signal strength (flux calibration); 3) correction of the receiver position in the focus of the parabolic dish because of shape variations (homologous distortion of the dish). The following properties are required for suitable calibration sources: strong compact sources with accurately determined position in the sky, precisely known radio fluxes at different wavelength bands and no variability in their flux. A number of quasars in particular fulfil all these properties. Thus some of the most regularly used calibrators for the 100 m radio telescope include galactic nuclei at distances between two (3C 273) and seven billion light years (3C 286).
3) Target Names and Catalogues
Some of the astronomical targets presented on the Galaxy Trail are simply named by their celestial coordinates. Examples include: J1148+5251 (Right Ascension 11h 48m, Declination +52o 51'), MG J0414+0534, B0218+367 and 0917+62. The other names are based on a number of different catalogues:
Messier Catalogue (M): Famous list of a total of 110 non-stellar objects (nebulae, clusters and galaxies), compiled by the French astronomer Charles Messier in the 18th century. The original intention was a negative list for his hunt for comets. Examples: M 31, M 82, M 87.
New General Catalogue (NGC): New General Catalogue of Nebulae and Clusters. A compilation of nebulae, clusters and galaxies all over the sky with a total of about 8000 entries. Examples: NGC 224 (M 31), NGC 1275, NGC 3034 (M 82), NGC 4486 (M 87).
Third Cambridge Catalogue (3C): Catalogue of radio sources from 1959. Most of the bright radio sources in the northern sky are contained in this catalogue. Examples: 3C 48, 3C 273, 3C 286, 3C 295, 3C 405.
Die stärksten Radioquellen am Himmel (Michael Hamm, 2006). A school work experience project at MPIfR (in German language), describing the strongest radio sources in a number of constellations. The label "Kosmische A-Klasse" (Cosmic Class A) describes optical observations of several of these sources (also in German). Examples: Andromeda A (M 31), Ursa Major A (M 82), Virgo A (M 87), Cygnus A (3C 405), Perseus A (NGC 1275).
Going back to ancient Babylon and Greece, observers of the night sky combined the bright dots of the stars to figures as background of several mythological tales. Orion, the hunter, Ursa Major, the great bear, with the distinctive part of the big dipper, Herkules or the 12 constellations of the zodiac from Aries, the ram, to Pisces, the fishes – some of these go all the way back to Sumerian or Babylonian times. Only in the 1920s, constellations in the sky were determined as well-defined areas in the sky. The complete sky was subdivided into 88 constellations of very different size (88 modern constellations). The coordinate of a celestial object defines the constellation it is referred to. Our neighbouring galaxy Messier 31 for example is found in the direction of Andromeda (thus: Andromeda galaxy or Andromeda nebula) and the most distant object on the Galaxy Trail, J1148+5251, is in the direction of Ursa Major, the great bear.
The story of the names of the constellations is described in the following: "How the Night Sky Constellations Got Their Names" (Joe Rao, space.com).