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		| Paper: | 
		Astrometry and Long Baseline Science | 
	 
	
		| Monograph: | 
		7, Science with a Next Generation Very Large Array | 
	 
	
		| Page: | 
		523 | 
	 
	
		| Authors: | 
		Reid, M.; Loinard, L.; Maccarone, T. | 
	 
	
	
		| Abstract: | 
		Recent advances in VLBI have led to astrometric accuracy exceeding that of the Gaia mission goals.   This chapter describes some important astrophysical problems  that can be addressed with sub-milliarcsecond imaging and μas astrometry using the ngVLA with long baselines. | 
	 
	
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