Arago telescope
Arago telescope, also known as Lunette Arago, is a 38 cm aperture refracting telescope at Paris Observatory. It was installed in 1857 after François Arago ordered it from the Lebreours company in 1839 and the instrument was completed by 1855. The telescope sits on the east tower’s dome, with an equatorial mount built by Brunner and a clock drive by Breguet.
Over the years, the telescope was upgraded: the original objective was re-polished in 1874, a new objective by the Henry Brothers was installed in the early 1880s, and the dome and mounting were updated, including replacing a wooden tube with iron.
The Arago telescope was used to study double stars, minor planets, and early photographic astronomy. It is noted for photometric observations of the Galilean satellites (Io, Europa, Callisto, Ganymede) in the 1880s and for photometric detections of eclipses of Jupiter’s moons in 1878. It supported observations with several photometers and used a Nicol prism in some setups. Between 1966 and 1971, more than 1,800 double stars were observed with the instrument. It also took part in PHEMU85 in 1985, a collaboration to study Jupiter’s moons.
To support the telescope’s weight, the Paris Observatory building was strengthened with a new cement base and a steel lattice.
This page was last edited on 2 February 2026, at 05:12 (CET).