The following properties are from K.R. Lang, 'Astrophysical
 
      Data: Planets and Stars', pp 70 and 73:
 
 
 
        Name:               J4 Callisto
 
                            (Jupiter VI)
 
        Distance from
 
          Jupiter Center:   1,880,000 km
 
                           (26.6 Jupiter radii)
 
        Orbital Period:     16.60 days
 
        Eccentricity:       0.010
 
        Inclination:        0.2 degrees
 
        Radius:             2400 km
 
        Mass:               1075x10^23 grams
 
        Density:            1.83 grams/cm^3
 
        Visual magnitude
 
          at opposition:    5.6
 
        Visual magnitude
 
          at unit distance,
 
          V(1,0):           -1.05
 
        Geometrical visual
 
          albedo:           0.17