GIER: A Danish computer from 1961 with a role in the modern revolution of astronomy

A Danish computer, GIER, from 1961 played a vital role in the development of a new method for astrometric measurement. This method, photon counting astrometry, ultimately led to two satellites with a significant role in the modern revolution of astronomy. A GIER was installed at the Hamburg Observatory in 1964 where it was used to implement the entirely new method for the measurement of stellar positions by means of a meridian circle, then the fundamental instrument of astrometry. An expedition to Perth in Western Australia with the instrument and the computer was a success. This method was also implemented in space in the first ever astrometric satellite Hipparcos launched by ESA in 1989. The Hipparcos results published in 1997 revolutionized astrometry with an impact in all branches of astronomy from the solar system and stellar structure to cosmic distances and the dynamics of the Milky Way. In turn, the results paved the way for a successor, the one million times more powerful Gaia astrometry satellite launched by ESA in 2013. Preparations for a Gaia successor in twenty years are making progress.Comment: 19 pages,8 figures, Accepted for publication in Nuncius Hamburgensis, Volume 2

The Astrometric Foundation of Astrophysics

Astrophysical studies require a knowledge of very accurate positions, motions and distances of stars. A brief overview is given of the significance and development of astrometry by ESA's two astrometric satellites, Hipparcos and Gaia, launched in respectively 1989 and 2013. The astrometric foundation of all branches of astronomy from the solar system and stellar systems to compact galaxies, quasars and dark matter is being revolutionized by the observations from these satellites. The future of fundamental astrometry must be considered in a time frame of 50 years, therefore science issues for a Gaia successor mission in twenty years are discussed in an extensive report: "Absolute astrometry in the next 50 years" available at http://arxiv.org/abs/1408.2190Comment: 2 pages, 2 figures, Abstract to the Conference Book 2014 of the Danish Astronomical Society and abstract of a revie

Interferometry from Space: A Great Dream

During some thirty years, 1980-2010, technical studies of optical interferometry from instruments in space were pursued as promising for higher spatial resolution and for higher astrometric accuracy. Nulling interferometry was studied for both high spatial resolution and high contrast. These studies were great dreams deserving further historical attention. ESA's interest in interferometry began in the early 1980s. The studies of optical interferometry for the global astrometry mission GAIA began in 1993 and ended in 1998 when interferometry was dropped as unsuited for the purpose, and the Gaia mission to be launched in 2013 is not based on interferometry. \c{opyright} Anita Publications. All rights reserved.Comment: 12 pages, 7 figures. In: Asian Journal of Physics Vol. 23, Nos 1 & 2 (2014), Special Issue on History of Physics & Astronomy, Guest Editor: Virginia Trimbl

Absolute astrometry in the next 50 years

With Gaia in orbit since December 2013 it is time to look at the future of fundamental astrometry and a time frame of 50 years is needed in this matter. A space mission with Gaia-like astrometric performance is required, but not necessarily a Gaia-like satellite. It should be studied whether this can be obtained within the budget of a medium-size ESA mission. A dozen science issues for a Gaia successor mission in twenty years, with launch about 2033, are presented and in this context also other possibilities for absolute astrometry with milliarcsecond (mas) or sub-mas accuracies are discussed. The three powerful techniques: VLBI, the MICADO camera on the E-ELT, and the LSST are described and documented by literature references and by an extensive correspondence with leading astronomers who readily responded with all the information I needed. In brief, the two Gaia-like missions would provide an astrometric foundation for all branches of astronomy from the solar system and stellar systems, including exo-planet systems, to compact galaxies, quasars and dark matter (DM) substructures by data which cannot be surpassed in the next 50 years. - In April 2017 ESA selected our proposal Hobbs et al. (2016) for study of a detector with NIR sensitivity for a Gaia successor mission, called GaiaNIR.Comment: 36 pages, 7 figures. Updates up to 12 June 2017 are included. Author - [email protected]