Dione

{{Infobox planet | name = Dione | mpc_name = Saturn IV | pronounced = | named_after = Διώνη Diōnē | adjectives = Dionean | image = Dione in natural light (cropped).jpg | caption = Dione photographed in natural light by theCassini spacecraft in 2008 | discoverer = Giovanni Cassini | discovered = March 30, 1684 | semimajor = | eccentricity = | period = | inclination = 0.019° (to Saturn's equator) | satellite_of = Saturn | dimensions = 1128.8 × 1122.6 × 1119.2 km | surface_area = | mean_radius = | mass = (1.834 Earths) | density = | surface_grav = m/s2 | escape_velocity = km/s | rotation = (synchronous) | axial_tilt = zero | albedo = (geometric) | magnitude = 10.4 | single_temperature = 87 K (−186°C) }} Dione, also designated Saturn IV, is the fourth-largest moon of Saturn. Its trailing hemisphere is marked by large ice cliffs called chasmata and is also darkened compared to the leading hemisphere. Based on its density, Dione’s interior is likely a combination of silicate rock and water ice in nearly equal parts by mass. The moon was discovered by Italian astronomer Giovanni Domenico Cassini in 1684 and is named after the Titaness Dione in Greek mythology. Name Giovanni Domenico Cassini named the four moons he discovered (Tethys, Dione, Rhea and Iapetus) Sidera Lodoicea ("the stars of Louis") to honor king Louis XIV. Cassini found Dione in 1684 using a large aerial telescope he set up on the grounds of the Paris Observatory. The satellites of Saturn were not named until 1847, when William Herschel's son John Herschel published Results of Astronomical Observations made at the Cape of Good Hope, suggesting that the names of the Titans (sisters and brothers of Cronus) be used. Orbit