The star observations carried out by Giuseppe Piazzi with Ramsden's large altazimuth circle, which he began in 1792, led to the realization of a 1st and 2nd Catalogue, published by Piazzi in Palermo in 1803 and 1814.
During 1845, the original astronomical observations in Piazzi's catalogue, included in “La storia celeste of the Palermo Observatory from 1792 to 1814”, which had been kept at the Brera Observatory in Milan, were published in Vienna.
The publication of these observational data revealed a series of errors, real or presumed, which cast doubt on the reliability of the Palermo Catalogue.
Towards the end of the last century, upon the suggestion of Giovanni Schiaparelli, work on the reduction of Piazzi's catalogue was once again taken up for the purpose of producing an independent catalogue based on the original observations. This work, carried out by Francesco Porro, led to the production of a corrected catalogue purged of systematic and accidental errors.
The third fundamental star catalogue of Palermo may represent the basis for the final reduction of the great Palermo Catalogue of 7646 stars.