Astrometry 1960-80: from Hamburg to Hipparcos By Erik Høg, 2013.07.03 Niels Bohr Institute, Copenhagen University ABSTRACT: Astrometry, the most ancient branch of astronomy, was facing extinction during much of the 20th century in the competition with astrophysics. The revival of astrometry came with the European astrometry satellite Hipparcos, approved by ESA in 1980 and launched 1989. Photon-counting astrometry was the basic measuring technique in Hipparcos, a technique invented by the author in 1960 in Hamburg. The technique was implemented on the Repsold meridian circle for the Hamburg expedition to Perth in Western Australia where it worked well during 1967- 72. This success paved the way for space astrometry, pioneered in France and implemented on Hipparcos. This report gives a detailed personal account of my life and work in Hamburg Bergedorf where I lived with my family half a century ago. The report is an accepted contribution to the proceedings of the meeting in Hamburg on 24 Sep. 2012 of Arbeitskreis Astronomiegeschichte of the Astronomische Gesellschaft. Gudrun Wolfschmidt is editor of the book: “Kometen, Sterne, Galaxien – Astronomie in Hamburg” zum 100jährigen Jubiläum der Hamburger Sternwarte in Bergedorf. Nuncius Hamburgensis, Beiträge zur Geschichte der Naturwissenschaften, Band 24, Hamburg: tredition 2013 The introduction and the table of contents of the book: https://dl.dropbox.com/u/49240691/100-HS3intro.pdf - 1 - Figure 12 Hamburg 1966 - The Repsold meridian circle ready for Perth The observer set the telescope to the declination as ordered by the assistant sitting with the star lists in the hut at left. He started the recording when he saw the star at the proper place in the field of view. Photo: Wilhelm Dieckvoss - 2 - 2013.07.03 Contents Photon-counting astrometry in Hamburg led to Hipparcos and Gaia 1 APPENDIX: Life and work in Hamburg 3 Towards astrophysics 3 Astrometry 1960-80: No return to Denmark 7 The new astrometry 7 from Hamburg to Hipparcos Return to astrometry with a great idea 10 By Erik Høg, Danish computer beats Niels Bohr Institute, Copenhagen University American by factor ten 15 email: [email protected] Building the instrument 17 Three ideas 21 Astrometry, the most ancient ABSTRACT: Australia 23 branch of astronomy, was facing extinction during Review of Perth 30 much of the 20th century in the competition with My life with people 31 astrophysics. The revival of astrometry came with Forty years after 36 the European astrometry satellite Hipparcos, Astrophysicists and astrometry 37 approved by ESA in 1980 and launched 1989. References 38 Photon-counting astrometry was the basic Note about figures 41 measuring technique in Hipparcos, a technique invented by the author in 1960 in Hamburg. The technique was implemented on the Repsold Here follows a short overview of the development meridian circle for the Hamburg expedition to leading to the Hipparcos and Gaia satellites while Perth in Western Australia where it worked well the appendix gives a detailed personal account of during 1967-72. This success paved the way for my life and work in Hamburg half a century ago. space astrometry, pioneered in France and implemented on Hipparcos. This report gives a My presentation at the meeting in Hamburg detailed personal account of my life and work in (Høg 2013) was similar to the one I gave at the Hamburg Bergedorf where I lived with my family conference in Tartu University in 2011 on the th half a century ago. occasion of the 200 anniversary of the Tartu Observatory, and the proceedings from that conference contains my talk (Høg 2011a). Photon-counting astrometry in Hamburg led to Hipparcos and Gaia On 1 October 1958 I arrived in Bergedorf with funding for 10 months from the Deutsche Akademische Austauschdienst. I wanted to get into astrophysics but my life developed very differently. I was pulled away from astrophysics when I invented a new technique for astrometry on 22 July 1960. The 10 months became 15 years, 1958-73. The new proposed astrometric technique, photon-counting astrometry (Høg 1960) found immediate recognition, but it took seven years to - 1 - implement it for the meridian circle in Bergedorf. The subsequent technical and scientific studies The technique was digital and applied slits and based on the new design resulted in the approval photon counting. The photon counts were of the Hipparcos mission in 1980 (see Høg 2011a recorded on punched tapes for later reduction in and b) which observed 1989-93. The astrometric the digital computer GIER. This was the first and photometric results from Hipparcos were application of photon counting in astrometry and published in 1997. They were improved for the the counts were tagged with high-precision timing bright stars in 2007 and provided a new basis for in Universal Time. The computer GIER of Danish astrophysics. For example, 719 stars obtained manufacture was installed in 1964. GIER was the distances with a standard error of 1% or better first computer on site in Bergedorf and after 1967 while only one star, the Sun, was known with a the first in the Perth Observatory in Western better accuracy before Hipparcos. Australia. The expedition to Perth 1967-72 with In 1992, during the Hipparcos mission, I eight observers from Hamburg and four from proposed the design principles for a new Perth was a great success resulting in the Perth70 astrometric mission Roemer (Høg 1993) which Catalogue in 1976 with accurate positions and would be nearly a million times more powerful photometry for 24900 stars. than Hipparcos. Such a mission was approved as The technique with slits and photon counting cornerstone mission of ESA in 2000 and is due for proposed in 1960 was quickly adopted in France launch in October 2013. This mission named Gaia where the V-shaped slit system was called “une is expected to obtain distances with 1% accuracy grille de Høg” and the technique was applied in or better for 11 million stars. It has been proposed the French work on space astrometry. The idea to give it a new name RGaia after launch, just as about astrometry from space was a French project MAP was renamed WMAP. This would recognize beginning in 1964 - a great French vision it truly the role of Roemer in actually starting the work was, especially due to Professor Pierre Lacroute towards Gaia and even in the right direction of (1967, 1974). direct scanning with CCDs, i.e. without the In those years, I myself and many others interferometry which was however very essential considered the French design of an astrometric in the original GAIA proposal of 1993, see Høg satellite to be completely unrealistic, but my (2011c). opinion about astrometry from space changed in Another fruit of my experiences from 1975. I was invited by ESA to join a small team Hamburg and Perth was the development of the for a mission study of space astrometry. At the automatic Carlsberg Meridian Circle, placed on first meeting in Paris on 14 October we were La Palma since 1984 and still in operation, see encouraged to forget about the specific French more in the appendix. It has been under remote design and only to think about how we could control since 1997, one of the first robotic make best use of space technology for our astronomical telescopes. science, astrometry. I returned to Denmark and six After leaving the Gaia Science Team in 2007, weeks later I had sent three reports about a quite I have written a dozen reports about the history of new design of the space instrument and mission. astrometry and optics during the past 2000 years This quick development was founded on the new (Høg 2008a and 2011d) and I have given talks on ideas from Copenhagen in the 1950s about the subject at two dozen places. After one of the astrometry, electronic instrumentation and digital talks a comment was this: “You said you wanted computing and after these ideas had grown on the to get into astrophysics fifty years ago, but by active and fertile grounds for astrometry in returning to revolutionize astrometry you have Bergedorf and Copenhagen/Brorfelde in the done more for astrophysics than you could have 1960s. done as an astrophysicist”. - 2 - Acknowledgements: I am grateful to William van 1. Towards astrophysics Altena, Craig Bowers, Andreas Burkert, Markiyan S. Chubey, Dafydd Evans, Claus Fabricius, Gerry Gilmore, Christian Gram, Rustem I. Gumerov, Klaus I left my home country, eager to learn and to work von der Heide, Ilse Holst, Birgitte Høg, Jean with astrophysics in Hamburg, and at the age of Kovalevsky, Bernd Loibl, Leslie Morrison, José Luis 26 years I was of course on the watch for girls, Muiños, Peter Naur, Finn Verner Nielsen, Jørgen especially the dream girl I could spend the rest of Otzen Petersen, Werner Pfau, Gennady I. Pinigin, Jochen Schramm, P. Kenneth Seidelmann, Chris my life with. Sterken, Anke Vollersen, Roderick Willstrop, Uwe Leaving Denmark before midnight was well Wolter and Norbert Zacharias for information and planned when I travelled to Germany by the night comments to previous versions of this report. When in train on 30 September 1958. When I did so I 2009 I first met Rajesh Kochhar, now president of the should not pay tax for the last quarter of the year IAU commission for the history of astronomy, he and I had always learned to think economically. insisted that I should write a book, my scientific The same did the Danish authorities who tried to biography. Without the encouragement from him, collect the tax, but in vain. I arrived early in the Gertie Skaarup, Gudrun Woldschmidt and last, but not day at the Hamburger Sternwarte in Bergedorf least from my dear wife Aase I could not have brought where I worked for the next 15 years, but that was all this together.