South Africa's Goverment Initiatives in Geodesy and the role of Astronomy

Aletha de Witt! ! Director: Radio Astronomy Projects ! Department of Science, Technology ! and Innovation (DSTI)! ! ! ! AfAS 2025, South Africa, 24 March 2025! ! Geodesy: Fundamental Astronomy ! Meeting Space Science for ! Global Impact" South Africa’s Government Initiatives in Geodesy and the Role of Astronomy 2 Credit: Heritage Malta Astronomy in South Africa •DSTI in collaboration with the Astronomy Community are in the process of renewing the Multi-wavelength Astronomy Strategy to be effective from 2025-2035 " •Importantly, Geodesy falls under Astronomy at a structural level —within the DSTI and NRF where it is managed as part of the astronomy portfolio under SARAO" •So what happens to Geodesy — the field that links the Earth and Sky, and underpins many of Astronomy’s most precise tools? 3 Credit: Heritage Malta Astronomy in South Africa •DSTI in collaboration with the Astronomy Community are in the process of renewing the Multi-wavelength Astronomy Strategy to be effective from 2025-2035 " •Importantly, Geodesy falls under Astronomy at a structural level —within the DSTI and NRF where it is managed as part of the astronomy portfolio under SARAO" •So what happens to Geodesy — the field that links the Earth and Sky, and underpins many of Astronomy’s most precise tools? ?Should geodesy be included in astronomy strategies — the same way we include other enablers like engineering, data science and computational infrastructure? 4 ?Credit: Heritage Malta Mnajdra, Malta ©2011 C.S. Jacobs, used by permission Credit: Heritage Malta Ancient Observations 5 Ancient Observations Astronomy goes back over 5000 years! Island of Malta’s monolithic temples Some of the oldest known human structures aligned with celestial events Credit: Heritage Malta Mnajdra, Malta ©2011 C.S. Jacobs, used by permission Credit: Heritage Malta At equinoxes, sunlight passes through the central doorway to light up a central stone. At solstices it illuminates specific megaliths — clear signs of intentional astronomical alignment! Astronomy is one of the oldest sciences — early people used astronomy to track time, structure rituals, and understand their place in the world!! 6 ?Credit: Heritage Malta Ancient Astronomers Wikipedia Wikipedia 7 ?Credit: Heritage Malta Ancient Astronomers Wikipedia Wikipedia —Hipparchus— Father of Scientific Astronomy! Created the first star catalog, discovered precession, invented idea of geographical coordinates, developed methods to convert between geographical and celestial coordinates —Ptolemy—! Architect of Classical Astronomy! Geocentric model of the Universe, star catalog of positions and magnitudes of almost 1000 stars, applied and expanded the geographical coordinate system ! 2nd century BCE 2nd century CE 8 ?Credit: Heritage Malta Modern History of Astronomy in Africa 9 ?Credit: Heritage Malta Modern History of Astronomy in Africa Nicolas de la Lacaille was sent to the Cape in the mid-1700s, as one of the first visiting astronomers, to map the southern skies. Why? Because during the 17th and 18th centuries, European explorers and traders faced serious navigational challenges along the southern African coastline. Lacaille’s work created some of the earliest southern star catalogs, and the observatory became a vital center for positional astronomy — laying the foundations for what we now know as SAAO Royal Observatory of the Cape of Good Hope (1820) Nicholas de la Caille First permanent observatory in Africa! 16 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration 17 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration 18 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Astrometric VLBI Geodetic VLBI 19 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration Astrometric VLBI Geodetic VLBI !Rely on the same fundamental observations - use the same radio telescopes, and the same schedule to observe the same AGN, and the fundamental data remains the same. The primary difference is the parameters that are solved for in data analysis. 20 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • Astrometric VLBI data for ICRF is also used to image and study AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration • weekly/monthly monitoring of 1000’s AGN • AGN high-resolution imaging and source structure >20,000 images at 22 GHz alone • multi-wavelength crosscorrelations in AGN • using VLBI to measure cosmic distances and independently estimate the Hubble constant • position and proper motion of Sgr A* • precise measurement of the Solar System’s galactocentric acceleration Astrometric VLBI Geodetic VLBI !Rely on the same fundamental observations - use the same radio telescopes, and the same schedule to observe the same AGN, and the fundamental data remains the same. The primary difference is the parameters that are solved for in data analysis. Astronomical VLBI 20 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • Astrometric VLBI data for ICRF is also used to image and study AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration • weekly/monthly monitoring of 1000’s AGN • AGN high-resolution imaging and source structure >20,000 images at 22 GHz alone • multi-wavelength crosscorrelations in AGN • using VLBI to measure cosmic distances and independently estimate the Hubble constant • position and proper motion of Sgr A* • precise measurement of the Solar System’s galactocentric acceleration Astrometric VLBI Geodetic VLBI !Rely on the same fundamental observations - use the same radio telescopes, and the same schedule to observe the same AGN, and the fundamental data remains the same. The primary difference is the parameters that are solved for in data analysis. Astronomical VLBI 20 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • Astrometric VLBI data for ICRF is also used to image and study AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration • weekly/monthly monitoring of 1000’s AGN • AGN high-resolution imaging and source structure >20,000 images at 22 GHz alone • multi-wavelength crosscorrelations in AGN • using VLBI to measure cosmic distances and independently estimate the Hubble constant • position and proper motion of Sgr A* • precise measurement of the Solar System’s galactocentric acceleration Astrometric VLBI Geodetic VLBI !Rely on the same fundamental observations - use the same radio telescopes, and the same schedule to observe the same AGN, and the fundamental data remains the same. The primary difference is the parameters that are solved for in data analysis. Astronomical VLBI 21 Astrometry, Astronomy, and Geodesy 22 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • Astrometric VLBI data for ICRF is also used to image and study AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration • weekly/monthly monitoring of 1000’s AGN • AGN high-resolution imaging and source structure >20,000 images at 22 GHz alone • multi-wavelength crosscorrelations in AGN • using VLBI to measure cosmic distances and independently estimate the Hubble constant • position and proper motion of Sgr A* • precise measurement of the Solar System’s galactocentric acceleration Astrometric VLBI Geodetic VLBI !Rely on the same fundamental observations - use the same radio telescopes, and the same schedule to observe the same AGN, and the fundamental data remains the same. The primary difference is the parameters that are solved for in data analysis. Astronomical VLBI 20 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • Astrometric VLBI data for ICRF is also used to image and study AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration • weekly/monthly monitoring of 1000’s AGN • AGN high-resolution imaging and source structure >20,000 images at 22 GHz alone • multi-wavelength crosscorrelations in AGN • using VLBI to measure cosmic distances and independently estimate the Hubble constant • position and proper motion of Sgr A* • precise measurement of the Solar System’s galactocentric acceleration Astrometric VLBI Geodetic VLBI !Rely on the same fundamental observations - use the same radio telescopes, and the same schedule to observe the same AGN, and the fundamental data remains the same. The primary difference is the parameters that are solved for in data analysis. Astronomical VLBI 20 Credit: Heritage Malta Astrometry, Astronomy, and Geodesy Absolute Astrometry (Celestial Reference Frames, AGN) A core discipline that underpins both astronomy and geodesy ?Geodesy • Measures Earth’s shape, rotation, and gravity field • Uses sky as reference Astronomy • Studies stars, galaxies, Universe • Observes celestial objects Astrometric VLBI • Precise celestial positions • Supports both fields Shared Tools • Radio telescopes • VLBI technique • Celestial Reference Frames •AGN • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • Astrometric VLBI data for ICRF is also used to image and study AGN • fixed external frame of reference • reference sources for geodetic VLBI observations to determine Earth orientation parameters (EOP) and contribute to ITRF • links the ICRF to the ITRF via EOP • Astrometric VLBI is Space Geodesy technique of the IAG • ICRF is a product of the IAG through the IVS • IVS is a service of IAG that coordinates geodetic and astrometric VLBI operations, analysis, and research • IVS is also a service of the IAU Geodetic VLBI, SLR, GNSS, DORIS — ITRF, EOP many applications • IAU commission A1 on Astrometry • ICRF working group • adopts a new ICRF • fixed frame of reference and calibrators • measuring positions and motions of celestial objects • enables high-precision multi-wavelength astrometry • supports deep-space navigation • planetary ephemeris • calibrate and align telescope pointing systems • test the theories of general and special relativity • Astrometric VLBI data for ICRF is also used to image and study AGN • ICR3, Dec 2020, A&A — 294 citation on ADS •ITRF for positions & changes in positions of telescopes on Earth & baseline vectors for VLBI (astronomy, astrometry, geodesy) •EOP to observe, track and locate celestial objects, ephemeris, space navigation, high-precision astrometry e.g. Gaia, !and high-precision timing studies for pulsar timing and gravitational wave detection • transforming from an Earth fixed frame to a celestial frame •GNSS-based ionosphere and tropospheric corrections, telescope clock synchronization & station position accuracy •Geodetic blocks in astronomical VLBI for calibration • weekly/monthly monitoring of 1000’s AGN • AGN high-resolution imaging and source structure >20,000 images at 22 GHz alone • multi-wavelength crosscorrelations in AGN • using VLBI to measure cosmic distances and independently estimate the Hubble constant • position and proper motion of Sgr A* • precise measurement of the Solar System’s galactocentric acceleration Astrometric VLBI Geodetic VLBI !Rely on the same fundamental observations - use the same radio telescopes, and the same schedule to observe the same AGN, and the fundamental data remains the same. The primary difference is the parameters that are solved for in data analysis. Astronomical VLBI 23 Ancient Observations Astronomy goes back over 5000 years! Island of Malta’s monolithic temples Some of the oldest known human structures aligned with celestial events Credit: Heritage Malta Mnajdra, Malta ©2011 C.S. Jacobs, used by permission Credit: Heritage Malta At equinoxes, sunlight passes through the central doorway to light up a central stone. At solstices it illuminates specific megaliths — clear signs of intentional astronomical alignment! Astronomy is one of the oldest sciences — early people used astronomy to track time, structure rituals, and understand their place in the world!! 24 ?Credit: Heritage Malta Ancient Astronomers Wikipedia Wikipedia —Hipparchus— Father of Scientific Astronomy! Created the first star catalog, discovered precession, invented idea of geographical coordinates, developed methods to convert between geographical and celestial coordinates —Ptolemy—! Architect of Classical Astronomy! Geocentric model of the Universe, star catalog of positions and magnitudes of almost 1000 stars, applied and expanded the geographical coordinate system ! 2nd century BCE 2nd century CE 25 ?Credit: Heritage Malta Modern History of Astronomy in Africa Nicolas de la Lacaille was sent to the Cape in the mid-1700s, as one of the first visiting astronomers, to map the southern skies. Why? Because during the 17th and 18th centuries, European explorers and traders faced serious navigational challenges along the southern African coastline. This laid the foundations for what we now know as the South African Astronomical Observatory (SAAO). Royal Observatory of the Cape of Good Hope (1820) Nicholas de la Caille First permanent observatory in Africa!