Umbriel 

Discovered by William Lassell in 1851, Umbriel is an old moon of Uranus roughly the size of Ariel, with a radial measurement of 584.7 kilometers and a mass of 1.27e+21 kilograms. The surface is full of large craters and has an interesting feature on the northern pole of the planet: a bright ring called the fluorescent cheerio (possibly a crater floor).

Physical Data Key Mass Mass Mass Mass compared to that of Earth. Radius Radius Radius Radius compared to that of Earth. Mean Density Average Density. Distance Distance to the planet's center. Magnitude The brightness of a star or object.

Orbital Data Key Rotational Period Number of days to make one complete rotation. Orbital Period Number of days to obital the planet. Mean Orbital Velocity Average obital speed. Orbital Eccentricity Eccentricity. Orbital Inclination The tilt of the moon or planet. Escape Escape Velocity. Albedo Visual geometric albedo.