Numerical simulations indicated a 10 mas accuracy level for Pan-STARRS astrometry, but experimental solutions on real data have not yet reached this level. If successful, this will be the first realization of a large optical astrometry catalog directly anchored to the ICRF. The grid catalog includes ~5000 extragalactic radio sources with VLBI-detected positions accurate to 1 mas or better, which are used as hard constraints to the astrometric unknowns in the global least-squares adjustment. Our approach is to solve a huge system of linear equations for a carefully selected set of ~1 million grid objects including the astrometric unknowns (positions, proper motions and parallaxes) and FoV calibration parameters. The absence of proper motions in 2MASS results in significant sky-correlated errors up to 30 - 50 mas. The 2MASS positions were used as reference for field of view (FoV) and detector calibration procedures. The current approach used in the data reduction pipeline is strictly differential. 1 In comparison, the Sun is 4.6 billion years old 6 and has a temperature of 5,778 K (5,505 ☌ 9,941 ☏). It has a temperature of 4,925 K (4,652 ☌ 8,405 ☏) and is 7 billion years old. One of these, the PS1 3 Survey, will repeatedly observe the entire sky north of 30 degrees, visiting every position 12 times in each of 5 filters. The 3PI survey performed by the PS1 telescope is well suited for a global astrometric solution. The star has a mass of 0.69 M and a radius of 0.64 R. A small collaboration of USNO and IfA astronomers is working on an improved astrometric solution for the data collected by the Pan-STARRS project.
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