When observing the comet of 1779 which had been discovered by Bode on Jan 6 and independently by Messier on Jan 18, he observed three "nebulous stars", namely M49, M60 and M61. M49 had been discovered 8 years earlier - in 1771 - by Charles Messier, while M60 had been discovered first by Koehler (together with M59 which Oriani has missed) on April 11, then by Oriani on April 12 and by Messier on April 15, 1779. M61, on the other hand, was the original discovery of Oriani on May 5, 1779, and was seen by Messier six days later; all these observations were made when the astronomers were following the comet.

Oriani became involved into the orbit calculation of Uranus after its discovery by William Herschel in March, 1781. After Saron, Lexell and others had shown that the object was not on a parabolic orbit and had obtained an approximate circular orbit, he calculated the planet's elliptical orbit in 1783. He improved this calculations for perturbations of Jupiter and Saturn in 1789.

Later, Oriani participated in geodesic surveys in France and Italy. A close friend of Piazzi, he worked with him on the orbit of the first known asteroid, Ceres, after its discovery in 1801.