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tokens: at epoch t , the catalog positions at t 0 would be corrected by applying the Galactic aberration model correction. We have investigated what is the effect of the aberration on estimated source positions. Figures 3 – 6 show the Calc/Solve differences in source positions (RA, Dec) versus RA and Dec for an aberration constant A G of 5.8 μ as yr −1 , which is the value we recommended for the IAU ICR3 solution as discussed below in Sect. 6 . The variation (scatter) of the differences at RA or Dec in these plots is due to the fact that the difference in the mean epochs from the chosen reference epoch 2015.0 vary significantly over the set of sources. The source position differences range over ±30–40 μ as. Fig. 3. Change in right ascension due to aberration versus right ascension with an aberration constant of 5.8 μ as yr −1 and reference epoch of 2015.0. Fig. 4. Change in right ascension due to aberration versus declination with an aberration constant of 5.8 μ as yr −1 and reference epoch of 2015.0. Fig. 5. Change in declination due to aberration versus right ascension with an aberration constant of 5.8 μ as yr −1 and reference epoch of 2015.0. Fig. 6. Change in declination due to aberration versus declination with an aberration constant of 5.8 μ as yr −1 and a reference epoch of 2015.0. 4. Estimates derived from Galactic astronomy measurements Aberration can also be derived from recent (2009–2017) Galactic astronomy measurements (e.g., Reid et al. 2014 ; Rastorguev et al. 2017 ; Brunthaler et al. 2011 ). These measurements are trigonometric parallaxes and proper motions of masers in high-mass star-forming regions in the Milky Way galaxy. The measurements were made using the Very Long Baseline Array (VLBA), the European VLBI network (EVN), and the Japanese VLBI Exploration of Radio Astronomy Project (VERA). The most recent investigation noted here ( Rastorguev et al. 2017 ), used a maser sample of 136 sources. Using these parallax and proper motion measurements, different investigators have derived models of the galaxy. Among the parameters of these models are the radial distance R 0 (kpc) to the Galactic center and circular rotation speed Θ 0 (km s −1 ) of the solar system barycenter around the Galactic center, which is located at a position with right ascension and declination of α G = 266.4° and δ G = −29.0° ( Reid Brunthaler 2004 ). To determine an aberration constant, we just consider the effect of the Local Standard of Rest (LSR) circular revolution with speed Θ 0 around the Galactic center. We note that there could be a small pecular acceleration an order of magnitude less than galactocentric acceleration due to solar motion with respect to the LSR as discussed in the introduction. Based on the estimated parameters R 0 and Θ 0 and their uncertainties from each investigator, one can determine the acceleration vector amplitude of (see Kovalevsky 2003 ) and its uncertainty assuming a circular orbit. This can be converted to an aberration