1. Spiru Haret made a fundamental contribution to the n-body problem in celestial mechanics by proving that using a third degree approximation for the disturbing forces implies instability of the major axes of the orbits, and by introducing the concept of secular perturbations in relation to this.
Spiru Haret was made a full member of the Romanian Academy in 1892.
Spiru Haret founded the Bucharest Astronomical Observatory, appointing Nicolae Coculescu as its first director.
Spiru Haret was born in Iasi, Moldavia, to Constantin and Smaranda Spiru Haret, who were of Armenian origin.
Spiru Haret started his studies in Dorohoi Iasi, and in 1862 moved to Saint Sava High School in Bucharest.
Spiru Haret showed an early talent for mathematics, publishing two textbooks when he was still a high school student.
Spiru Haret was appointed professor of rational mechanics at the Faculty of Science of the University of Bucharest.
The next year, Spiru Haret became a correspondent member of the Romanian Academy, receiving full membership in 1892.
Spiru Haret kept the professorship at the Faculty of Science until his retirement in 1910, when he was followed as professor of mechanics by Dimitrie Pompeiu.
Spiru Haret died in Bucharest in 1912 of cancer, and was buried in the city's Bellu Cemetery; Ana Spiru Haret died in 1941, aged 74.
Spiru Haret established the instability of the model of the n-body problem assuming frequencies to be incommensurable; Poincare took into account commensurabilities, and using generalized Fourier series, he proved the divergence of these series, thus confirming Spiru Haret's result.
Spiru Haret only published an article on the secular acceleration of the Moon in 1880 and one on Jupiter's Great Red Spot.