Discovery and Naming of Calypso
Saturn has different groups of moons: ring shepherds, irregular moons, Trojan moons, and co-orbitals.
Before the launch of spacecraft like Voyager and Cassini these moons of Saturn were identified through observations from Earth. In March 1980, D. Pascu, P.K. Seidelmann, W. Baum and D. Currie discovered Calypso, a small, irregularly shaped moon of Saturn using ground based telescopic observations. Both Calypso and Telesto were discovered in the same year and were named after goddesses in Greek mythology. Tethys was discovered in 1684 by G.D. Cassini. According to Greek mythology, Tethys had two daughters Telesto and Calypso. Thus the moons which share the orbit with Tethys were named after the daughters of the goddess.
The Trojan moons are a special feature of Saturn. There are four Trojan moons and Calypso is one among them. Calypso, and another moon, Telesto revolve around Saturn in the same orbit as the moon Tethys, and are called Tethys Trojans. They occupy a special region called Lagrangian Points, where both experience gravitational stability. In this region the gravitational force of Saturn is balanced by that of Tethys. Calypso is 60°behind Tethys and hence is the trailing Trojan, whereas Telesto is ahead of Tethys by the same angle.
The other two Trojan moons are Helene and Polydeuces, but they share an orbit with the moon Dione.