Uranus Fact Sheet

Uranus

Uranus/Earth Comparison

Bulk parameters

                                    Uranus      Earth   Ratio (Uranus/Earth)
Mass (1024 kg)                      86.816      5.9726        14.536
Volume (1010 km3)                    6,833    108.321         63.08
Radius (1 bar level) (km)
    Equatorial                      25,559      6,378.1        4.007
    Polar                           24,973      6,356.8        3.929
Volumetric mean radius (km)         25,362      6,371.0        3.981
Ellipticity (Flattening)             0.02293    0.00335        6.84
Mean density (kg/m3)                 1,271      5,514          0.231
Gravity (eq., 1 bar) (m/s2)          8.87       9.80           0.905
Acceleration (eq., 1 bar) (m/s2)     8.69       9.78           0.889
Escape velocity (km/s)              21.3       11.19           1.903
GM (x 106 km3/s2)                    5.794      0.3986        14.536
Bond albedo                          0.300      0.306          0.980
Visual geometric albedo              0.51       0.367          1.390
Visual magnitude V(1,0)             -7.19      -3.86             -
Solar irradiance (W/m2)              3.71       1,367.6        0.0027
Black-body temperature (K)          58.2      254.3            0.229
Moment of inertia (I/MR2)            0.225      0.3308         0.680
J2 (x 10-6)                       3343.43    1082.63           3.088    
Number of natural satellites        27          1
Planetary ring system              Yes         No

Orbital parameters

                                    Uranus      Earth   Ratio (Uranus/Earth)
Semimajor axis (106 km)            2,872.46      149.60       19.201
Sidereal orbit period (days)      30,685.4       365.256      84.011   
Tropical orbit period (days)      30,588.740     365.242      83.749
Perihelion (106 km)                2,741.30      147.09       18.637     
Aphelion (106 km)                  3,003.62      152.10       19.748
Synodic period (days)                369.66        -             -
Mean orbital velocity (km/s)           6.80       29.78        0.228    
Max. orbital velocity (km/s)           7.11       30.29        0.235        
Min. orbital velocity (km/s)           6.49       29.29        0.222       
Orbit inclination (deg)                0.772       0.000         -
Orbit eccentricity                     0.0457      0.0167      2.737
Sidereal rotation period (hours)     -17.24*      23.9345      0.720
Length of day (hrs)                   17.24       24.0000      0.718
Obliquity to orbit (deg)              97.77       23.44        4.171

* Magnetic coordinates (as determined by the Voyager 2 Radio Science experiment)

Uranus Observational Parameters

Discoverer:      William Herschel
Discovery Date:  13 March 1781

Distance from Earth
        Minimum (106 km)         2581.9
        Maximum (106 km)         3157.3
Apparent diameter from Earth
        Maximum (seconds of arc)    4.1
        Minimum (seconds of arc)    3.3
Mean values at opposition from Earth
        Distance from Earth (106 km)       2719.99    
        Apparent diameter (seconds of arc)    3.9
        Apparent visual magnitude             5.5  
Maximum apparent visual magnitude             5.32

Uranus Mean Orbital Elements (J2000)

Semimajor axis (AU)                 19.19126393  
Orbital eccentricity                 0.04716771   
Orbital inclination (deg)            0.76986   
Longitude of ascending node (deg)   74.22988  
Longitude of perihelion (deg)      170.96424  
Mean Longitude (deg)               313.23218

North Pole of Rotation

Right Ascension: 257.43
Declination    : -15.10
Reference Date : 12:00 UT 1 Jan 2000 (JD 2451545.0)

Uranian Magnetosphere

Dipole field strength: 0.228 gauss-Ru3
Dipole tilt to rotational axis: 58.6 degrees
Dipole offset (planet center to dipole center) distance: 0.3 Ru along the rotation axis

Note: Ru denotes Uranian radii, here defined to be 25,600 km

Uranian Atmosphere

Surface Pressure: >>1000 bars  
Temperature at 1 bar: 76 K (-197 C)
Temperature at 0.1 bar: 53 K (-220 C)
Density at 1 bar: 0.42 kg/m3
Wind speeds: 0-250 m/s
Scale height: 27.7 km
Mean molecular weight: 2.64 g/mole
Atmospheric composition (by volume, uncertainty in parentheses)
    Major:       Molecular hydrogen (H2) - 82.5% (3.3%); Helium (He) - 15.2% (3.3%)
                 Methane (CH4) - 2.3%
    Minor (ppm): Hydrogen Deuteride (HD) - 148
    Aerosols:    Ammonia ice, water ice, ammonia hydrosulfide, methane ice(?)

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