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The light from a source at a distance d will arrive at detectors separated by 100 AU at times that differ by as much as 120 (d/100 Mpc)^{-1} nanoseconds because of the curvature of the wavefront. At gigahertz frequencies, the arrival time…

We present the results of PSR$\pi$, a large astrometric project targeting radio pulsars using the Very Long Baseline Array (VLBA). From our astrometric database of 60 pulsars, we have obtained parallax-based distance measurements for all…

The large constellations of spacecraft planned for use in cislunar space (on the Lunar surface, in Lunar orbit, and in the vicinity of the Lunar Gateway) require new solutions for positioning, navigation and timing (PNT). Here, I describe…

Advancements in VLBI instrumentation, driven by the geodetic community's goal of achieving positioning accuracy of 1 mm and stability of 0.1 mm/y, have led to the development of new broadband systems. Here, we assess the potential of these…

It is expected that the European Space Agency mission Gaia will make possible to determine coordinates in the optical domain of more than 500000 quasars. In 2006, a radio astrometry project was launched with the overall goal to make…

This paper discusses the Cosmic Background (CB) dipoles observations in the framework of the Planck mission. Dipoles observations can be used in three ways: (i) It gives a measurement of the peculiar velocity of our Galaxy which is an…

In recent years, large radio surveys of Active Galactic Nuclei (AGNs), comprising millions of sources, have become available where one could investigate dipole asymmetries, assumedly arising due to a peculiar motion of the Solar system.…

A catalog containing milliarcsecond--accurate positions of 1332 extragalactic radio sources distributed over the northern sky is presented - the Very Long Baseline Array Calibrator Survey (VCS1). The positions have been derived from…

The space astrometry mission GAIA will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the GAIA frame and the International Celestial…

We describe a data reduction pipeline for VLBI astrometric observations of pulsars, implemented using the ParselTongue AIPS interface. The pipeline performs calibration (including ionosphere modeling), phase referencing with proper…

The Cosmic Microwave Background (CMB) radiation offers a unique window into the early Universe, facilitating precise examinations of fundamental cosmological theories. However, the quest for detecting B-modes in the CMB, predicted by…

We examine the sky distribution of radio galaxies in the NRAO VLA Sky Survey (NVSS) and the Rapid ASKAP Continuum Survey (RACS). Analyses of these samples have reported tension between their inferred dipoles and the kinematic dipole of the…

Obtaining pulsar parallaxes via relative astrometry (also known as differential astrometry) yields distances and transverse velocities that can be used to probe properties of the pulsar population and the interstellar medium. Large programs…

Observations of Interplanetary Scintillation (IPS) are an efficient remote-sensing method to study the solar wind and inner heliosphere. From 2016 to 2018, some distinctive observations of IPS sources like 3C 286 and 3C 279 were…

Precise millisecond pulsar (MSP) positions determined with very long baseline interferometry (VLBI) hold the key to building the connection between the kinematic and dynamic reference frames respectively used by VLBI and pulsar timing. The…

It is anticipated that future space-born missions, such as Gaia, will be able to determine in optical domain positions of more than 100,000 bright quasars with sub-mas accuracies that are comparable to very long baseline interferometry…

The C-Band All-Sky Survey (C-BASS) is an all-sky full-polarisation survey at a frequency of 5 GHz, designed to provide complementary data to the all-sky surveys of WMAP and Planck, and future CMB B-mode polarization imaging surveys. The…

Published analyses of very long baseline interferometry (VLBI) data for the sources included in the third International Celestial Reference Frame (ICRF3) catalog have revealed object-specific, excess astrometric variability and…

The use of the phase-delay improves substantially the accuracy obtained in VLBI astrometry with respect to the group-delay observable. Recently, Ros et al. (1999) have extended the related phase-connection technique to a triangle of radio…

This paper presents accurate absolute positions from a 24 GHz Very Long Baseline Array (VLBA) search for compact extragalactic sources in an area where the density of known calibrators with precise coordinates is low. The goals were to…