In 1865 he founded the specialist physical astronomy journal, Memorie della Società degli Spettroscopisti, and remained the editor until 1905.

Tacchini established an observation network with other Italian astronomers to spectroscopically examine the sun at about the same time daily.

He likewise organized an observatory in Calcutta to watch the sun when conditions were unfavorable in Italy.

In 1879 he was summoned to Rome where he succeeded Angelo Secchi at the Osservatorio del Collegio Romano.

Due to his influence, the Bellini Observatory was completed on Mount Etna where Pietro believed that the high altitude would improve the spectroscopic observations of the sun, and potentially allow direct observations of the solar corona without an eclipse.