Iapetus
Iapetus
Moon
Pisces
Visible
Level 6
Professional/Research - Timing dependent
Properties
Magnitude
10.2
Angular Size
0.2 arcmin
Type: Moon
Distance: 0.024 AU
Orbital Period: 79.3 days
Diameter: 1,469 km
Features: Dark Cassini Regio, bright Roncevaux Terra, equatorial ridge
Dramatic two-toned surface: bright trailing hemisphere (mag 10.2) and dark leading hemisphere (mag 11.9). Cassini noticed it was visible only on one side of Saturn. Far from Saturn, so easier to separate. Requires 6 inch telescope.
Position & Identifiers
RA
00h 21m 37.0s
Dec
+00° 00' 42.2"
Constellation
Pisces
Catalog
Iapetus
Physical Properties
Diameter
1,469 km
(0.12× Earth)
Mass
1.81e21 kg
Albedo
0.25
(25% reflected)
Temperature
-173°C to -143°C
Rotation
79.3 days
Surface
Dark Cassini Regio, bright Roncevaux Terra, equatorial ridge
Angular Size
0.2″ (current)
Orbital Properties
Semi-major Axis
0.0238 AU
(3,561,028 km)
Eccentricity
0.0286
Inclination
15.47°
Orbital Period
79.3 days
Distance
10.517 AU
(1.46 light-hours)
Elongation
2.5°
Near Sun
Observing Tips
Best Months
April
, May
, June
Visibility
Telescope
Where to Look
Near Saturn
Notes
Dramatic two-toned surface: bright trailing hemisphere (mag 10.2) and dark leading hemisphere (mag 11.9). Cassini noticed it was visible only on one side of Saturn. Far from Saturn, so easier to separate. Requires 6 inch telescope.
Parent Body
Discovery
Discovered by
Giovanni Cassini
Date
1671-10-25
Current Ephemeris
10.517
AU from Earth
1.57B
km
0.2″
Angular Size
2°
Elongation
Visibility
Set a location in User Settings to see visibility data.
Community Photos (1)
Credit: NASA / JPL / SSI / Gordan Ugarkovic. License: CC BY-SA 2.5. (Wikimedia Commons)
Skybred Feb 28, 2026