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Published online by Cambridge University Press: 14 August 2015
Since 1953 regular observations have been made with the polar photographic tube at Pulkovo, a fixed astrograph (D = 20 cm, F = 600 cm), which can take photographs of a circumpolar zone of 60′ radius (Bakhrakh, 1971). An analysis of measured polar distances of the same 30 stars on each plate gives corrections to the adopted values of the constants of aberration and precession and of the coefficients of nutation. At present the determination of the coefficients of the short-period semi-annual solar and fortnightly nutations is of greatest interest, as they are affected most by the Earth's liquid core.