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About Uranus Planet | Solar System

Uranus

Uranus (from the Latin name Ūranus for the Greek god Οὐρανός) is the seventh planet from the Sun after Saturn. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn. 
Uranus Planet
Uranus Planet

For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants. Uranus' atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more "ices" such as water, ammonia, and methane, along with traces of other hydrocarbons. Uranus is the seventh planet from the Sun and is the third largest in the solar system. It was discovered by William Herschel in 1781. It has an equatorial diameter of 51,800 kilometers (32,190 miles) and orbits the Sun once every 84.01 Earth years.


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Physical characteristics

The total mass of ice in Uranus' interior is not precisely known, because different figures emerge depending on the model chosen; it must be between 9.2 and 13.6 Earth masses.Hydrogen and helium constitute only a small part of the total, with between 0.5 and 1.5 Earth masses. The remainder of the non-ice mass (0.5 to 3.8 Earth masses) is accounted for by rocky material. 


Internal structure Uranus
Internal structure Uranus

Our knowledge of the internal structure of Uranus is inferred from the planet's radius, mass, period of rotation, the shape of its gravitational field and the behavior of hydrogen, helium, and water at high pressure. Its internal structure is similar to that of Neptune except for the fact that it is less active in terms of atmospheric dynamics and interior heat flow.

Uranus' Rings

In 1977, the first nine rings of Uranus were discovered. During the Voyager encounters, these rings were photographed and measured, as were two other new rings and ringlets. Uranus' rings are distinctly different from those at Jupiter and Saturn. The outermost epsilon ring is composed mostly of ice boulders several feet across. A very tenuous distribution of fine dust also seems to be spread throughout the ring system.

There may be a large number of narrow rings, or possibly incomplete rings or ring arcs, as small as 51 meters (161 feet) in width. The individual ring particles were found to be of low reflectivity. At least one ring, the epsilon, was found to be gray in color. The moons Cordelia and Ophelia act as shepherd satellites for the epsilon ring.


Moons

Uranus has 27 known natural satellites. The names of these satellites are chosen from characters in the works of Shakespeare and Alexander Pope. The five main satellites are Miranda, Ariel, Umbriel, Titania, and Oberon. 


Uranus Moon

The Uranian satellite system is the least massive among those of the giant planets; the combined mass of the five major satellites would be less than half that of Triton (largest moon of Neptune) alone. The largest of Uranus' satellites, Titania, has a radius of only 787.9 km, or less than half that of the Moon, but slightly more than Rhea, the second-largest satellite of Saturn, making Titania the eighth-largest moon in the Solar System. Uranus' satellites have relatively low albedos; ranging from 0.20 for Umbriel to 0.35 for Ariel (in green light). They are ice–rock conglomerates composed of roughly 50% ice and 50% rock. The ice may include ammonia and carbon dioxide.

Discovery


Uranus had been observed on many occasions before its recognition as a planet, but it was generally mistaken for a star. Possibly the earliest known observation was by Hipparchos, who in 128 BC might have recorded it as a star for his star catalogue that was later incorporated into Ptolemy's Almagest. 

William Herschel, discoverer of Uranus in 1781
William Herschel, discoverer of Uranus in 1781

The earliest definite sighting was in 1690, when John Flamsteed observed it at least six times, cataloguing it as 34 Tauri. The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 1750 and 1769, including on four consecutive nights.



Uranus Statistics


Discovered by
William Herschel
Date of discovery
1781
Mass (kg)
8.686e+25
Mass (Earth = 1)
1.4535e+01
Equatorial radius (km)
25,559
Equatorial radius (Earth = 1)
4.0074
Mean density (gm/cm^3)
1.29
Mean distance from the Sun (km)
2,870,990,000
Mean distance from the Sun (Earth = 1)
 19.1914
Rotational period (hours)
-17.9
Orbital period (years)
84.01
Mean orbital velocity (km/sec)
6.81
Orbital eccentricity
0.0461
Tilt of axis (degrees)
97.86
Orbital inclination (degrees)
0.774
Equatorial surface gravity (m/sec^2)
7.77
Equatorial escape velocity (km/sec)
21.30
Visual geometric albedo
0.51
Magnitude (Vo)
5.52
Mean cloud temperature
-193°C
Atmospheric pressure (bars)
1.2
Atmospheric composition
Hydrogen
Helium
Methane

83%
15%
2%

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