Moment of inertia factor
Sidereal rotation period
2995379362880000000♠−0.71833 d (retrograde)
17 h 14 min 24 s
Equatorial rotation velocity
97.77° (to orbit)
North pole right ascension
17h 9m 15s
North pole declination
1 bar level
76 K (−197.2 °C)
5.9 to 5.32
3.3″ to 4.1″
Composition by volume
(Below 1.3 bar)
83 ± 3% hydrogen (H2)
15 ± 3% helium (He)
2.3% methane (CH4)
0.009% (0.007–0.015%) hydrogen deuteride (HD)
ammonium hydrosulfide (NH4SH)
Uranus is the seventh planet from the Sun. It has the third-largest
planetary radius and fourth-largest planetary mass in the Solar
Uranus is similar in composition to Neptune, and both have
different bulk chemical composition from that of the larger gas giants
Jupiter and Saturn. For this reason, scientists often classify Uranus
Neptune as "ice giants" to distinguish them from the gas giants.
Uranus's 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. It is the coldest planetary atmosphere in the Solar
System, with a minimum temperature of 49 K (−224 °C;
−371 °F), and has a complex, layered cloud structure with
water thought to make up the lowest clouds and methane the uppermost
layer of clouds. The interior of
Uranus is mainly composed of ices
Uranus is the only planet whose name is derived directly from a figure
from Greek mythology, from the Latinised version of the Greek god of
the sky Ouranos. Like the other giant planets,
Uranus has a ring
system, a magnetosphere, and numerous moons. The Uranian system has a
unique configuration among those of the planets because its axis of
rotation is tilted sideways, nearly into the plane of its solar orbit.
Its north and south poles, therefore, lie where most other planets
have their equators. In 1986, images from
Voyager 2 showed Uranus
as an almost featureless planet in visible light, without the cloud
bands or storms associated with the other giant planets.
Earth have shown seasonal change and increased
weather activity as
Uranus approached its equinox in 2007. Wind speeds
can reach 250 metres per second (900 km/h; 560 mph).
2 Orbit and rotation
2.1 Axial tilt
3 Physical characteristics
3.1 Internal structure
3.1.1 Internal heat
3.2.3 Upper atmosphere
4.1 Banded structure, winds and clouds
4.2 Seasonal variation
6.1 Planetary rings
8 In culture
9 See also
12 Further reading
13 External links
Like the classical planets,
Uranus is visible to the naked eye, but it
was never recognised as a planet by ancient observers because of its
dimness and slow orbit. Sir
William Herschel announced its
discovery on 13 March 1781, expanding the known boundaries of the
Solar System for the first time in history and making
Uranus the first
planet discovered with a telescope.
"34 Tauri" redirects here. For the Firefly Verse, see List of Firefly
planets and moons.
William Herschel, discoverer of Uranus
Replica of the telescope used by Herschel to discover Uranus
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. 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.
William Herschel observed
Uranus on 13 March 1781 from the garden
of his house at 19 New King Street in Bath, Somerset, England (now the
Herschel Museum of Astronomy), and initially reported it (on 26
April 1781) as a comet. Herschel "engaged in a series of
observations on the parallax of the fixed stars", using a
telescope of his own design.
Herschel recorded in his journal: "In the quartile near ζ
Tauri ... either [a] Nebulous star or perhaps a comet." On 17
March he noted: "I looked for the
Comet or Nebulous Star and found
that it is a Comet, for it has changed its place." When he
presented his discovery to the Royal Society, he continued to assert
that he had found a comet, but also implicitly compared it to a
The power I had on when I first saw the comet was 227. From experience
I know that the diameters of the fixed stars are not proportionally
magnified with higher powers, as planets are; therefore I now put the
powers at 460 and 932, and found that the diameter of the comet
increased in proportion to the power, as it ought to be, on the
supposition of its not being a fixed star, while the diameters of the
stars to which I compared it were not increased in the same ratio.
Moreover, the comet being magnified much beyond what its light would
admit of, appeared hazy and ill-defined with these great powers, while
the stars preserved that lustre and distinctness which from many
thousand observations I knew they would retain. The sequel has shown
that my surmises were well-founded, this proving to be the
have lately observed.
Herschel notified the
Nevil Maskelyne of his
discovery and received this flummoxed reply from him on 23 April 1781:
"I don't know what to call it. It is as likely to be a regular planet
moving in an orbit nearly circular to the sun as a
Comet moving in a
very eccentric ellipsis. I have not yet seen any coma or tail to
Although Herschel continued to describe his new object as a comet,
other astronomers had already begun to suspect otherwise.
Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was
the first to compute the orbit of the new object. Its nearly
circular orbit led him to a conclusion that it was a planet rather
than a comet. Berlin astronomer
Johann Elert Bode
Johann Elert Bode described Herschel's
discovery as "a moving star that can be deemed a hitherto unknown
planet-like object circulating beyond the orbit of Saturn". Bode
concluded that its near-circular orbit was more like a planet than a
The object was soon universally accepted as a new planet. By 1783,
Herschel acknowledged this to
Royal Society president Joseph Banks:
"By the observation of the most eminent
Astronomers in Europe it
appears that the new star, which I had the honour of pointing out to
them in March 1781, is a Primary
Planet of our Solar System." In
recognition of his achievement, King George III gave Herschel an
annual stipend of £200 on condition that he move to Windsor so that
the Royal Family could look through his telescopes.
The name of
Uranus references the ancient Greek deity of the sky
Uranus (Ancient Greek: Οὐρανός), the father of
and grandfather of
Zeus (Jupiter), which in Latin became "Ūranus"
(Latin pronunciation: [ˈuːranʊs]). It is the only planet
whose name is derived directly from a figure of Greek mythology. The
adjectival form of
Uranus is "Uranian". The pronunciation of the
Uranus preferred among astronomers is /ˈjʊərənəs/, with
stress on the first syllable as in Latin Ūranus, in contrast to
/jʊəˈreɪnəs/, with stress on the second syllable and a long a,
though both are considered acceptable.[f]
Consensus on the name was not reached until almost 70 years after the
planet's discovery. During the original discussions following
discovery, Maskelyne asked Herschel to "do the astronomical world the
faver [sic] to give a name to your planet, which is entirely your
own, [and] which we are so much obliged to you for the discovery
of". In response to Maskelyne's request, Herschel decided to name
the object Georgium Sidus (George's Star), or the "Georgian Planet" in
honour of his new patron, King George III. He explained this
decision in a letter to Joseph Banks:
In the fabulous ages of ancient times the appellations of Mercury,
Saturn were given to the Planets, as being
the names of their principal heroes and divinities. In the present
more philosophical era it would hardly be allowable to have recourse
to the same method and call it Juno, Pallas, Apollo or Minerva, for a
name to our new heavenly body. The first consideration of any
particular event, or remarkable incident, seems to be its chronology:
if in any future age it should be asked, when this last-found Planet
was discovered? It would be a very satisfactory answer to say, 'In the
reign of King George the Third'.
Herschel's proposed name was not popular outside Britain, and
alternatives were soon proposed. Astronomer
Jérôme Lalande proposed
that it be named Herschel in honour of its discoverer. Swedish
Erik Prosperin proposed the name Neptune, which was
supported by other astronomers who liked the idea to commemorate the
victories of the British Royal Naval fleet in the course of the
American Revolutionary War
American Revolutionary War by calling the new planet even Neptune
George III or
Neptune Great Britain.
In a March 1782 treatise, Bode proposed Uranus, the Latinised version
of the Greek god of the sky, Ouranos. Bode argued that the name
should follow the mythology so as not to stand out as different from
the other planets, and that
Uranus was an appropriate name as the
father of the first generation of the Titans. He also noted that
elegance of the name in that just as
Saturn was the father of Jupiter,
the new planet should be named after the father of
Saturn. In 1789, Bode's Royal Academy colleague Martin
Klaproth named his newly discovered element uranium in support of
Bode's choice. Ultimately, Bode's suggestion became the most
widely used, and became universal in 1850 when HM Nautical Almanac
Office, the final holdout, switched from using Georgium Sidus to
Uranus has two astronomical symbols. The first to be proposed, ♅,[g]
was suggested by Lalande in 1784. In a letter to Herschel, Lalande
described it as "un globe surmonté par la première lettre de votre
nom" ("a globe surmounted by the first letter of your surname"). A
later proposal, ⛢,[h] is a hybrid of the symbols for
Mars and the
Uranus was the Sky in Greek mythology, which was thought
to be dominated by the combined powers of the
Sun and Mars.
Uranus is called by a variety of translations in other languages. In
Chinese, Japanese, Korean, and Vietnamese, its name is literally
translated as the "sky king star" (天王星). In
Thai, its official name is Dao Yurenat
(ดาวยูเรนัส), as in English. Its other name in
Thai is Dao Maritayu (ดาวมฤตยู, Star of Mṛtyu),
after the Sanskrit word for "death",
Mrtyu (मृत्यु). In
Mongolian, its name is Tengeriin Van (Тэнгэрийн ван),
translated as "King of the Sky", reflecting its namesake god's role as
the ruler of the heavens. In Hawaiian, its name is Hele‘ekala. In
Māori, its name is Whērangi.
Orbit and rotation
A 1998 false-colour near-infrared image of
Uranus showing cloud bands,
rings, and moons obtained by the Hubble Space Telescope's NICMOS
Uranus orbits the
Sun once every 84 years. Its average distance from
Sun is roughly 20 AU (3 billion km;
2 billion mi). The difference between its minimum and
maximum distance from the
Sun is 1.8 AU, larger than that of any other
planet, though not as large as that of pluto, the nearest dwarf
planet. The intensity of sunlight varies inversely with the square
of distance, and so on
Uranus (at about 20 times the distance from the
Sun compared to Earth) it is about 1/400 the intensity of light on
Earth. Its orbital elements were first calculated in 1783 by
Pierre-Simon Laplace. With time, discrepancies began to appear
between the predicted and observed orbits, and in 1841, John Couch
Adams first proposed that the differences might be due to the
gravitational tug of an unseen planet. In 1845, Urbain Le Verrier
began his own independent research into Uranus's orbit. On 23
Johann Gottfried Galle
Johann Gottfried Galle located a new planet, later
named Neptune, at nearly the position predicted by Le Verrier.
The rotational period of the interior of
Uranus is 17 hours,
14 minutes. As on all the giant planets, its upper atmosphere
experiences strong winds in the direction of rotation. At some
latitudes, such as about 60 degrees south, visible features of the
atmosphere move much faster, making a full rotation in as little as 14
The Uranian axis of rotation is approximately parallel with the plane
of the Solar System, with an axial tilt of 97.77° (as defined by
prograde rotation). This gives it seasonal changes completely unlike
those of the other planets. Near the solstice, one pole faces the Sun
continuously and the other faces away. Only a narrow strip around the
equator experiences a rapid day–night cycle, but with the
over the horizon. At the other side of Uranus's orbit the orientation
of the poles towards the
Sun is reversed. Each pole gets around
42 years of continuous sunlight, followed by 42 years of
darkness. Near the time of the equinoxes, the
Sun faces the
Uranus giving a period of day–night cycles similar to
those seen on most of the other planets.
Uranus reached its most recent equinox on 7 December 2007.
One result of this axis orientation is that, averaged over the Uranian
year, the polar regions of
Uranus receive a greater energy input from
Sun than its equatorial regions. Nevertheless,
Uranus is hotter at
its equator than at its poles. The underlying mechanism that causes
this is unknown. The reason for Uranus's unusual axial tilt is also
not known with certainty, but the usual speculation is that during the
formation of the Solar System, an Earth-sized protoplanet collided
with Uranus, causing the skewed orientation. Uranus's south pole
was pointed almost directly at the
Sun at the time of Voyager 2's
flyby in 1986. The labelling of this pole as "south" uses the
definition currently endorsed by the International Astronomical Union,
namely that the north pole of a planet or satellite is the pole that
points above the invariable plane of the Solar System, regardless of
the direction the planet is spinning. A different convention
is sometimes used, in which a body's north and south poles are defined
according to the right-hand rule in relation to the direction of
From 1995 to 2006, Uranus's apparent magnitude fluctuated between +5.6
and +5.9, placing it just within the limit of naked eye visibility at
+6.5. Its angular diameter is between 3.4 and 3.7 arcseconds,
compared with 16 to 20 arcseconds for
Saturn and 32 to
45 arcseconds for Jupiter. At opposition,
Uranus is visible
to the naked eye in dark skies, and becomes an easy target even in
urban conditions with binoculars. In larger amateur telescopes with
an objective diameter of between 15 and 23 cm,
Uranus appears as
a pale cyan disk with distinct limb darkening. With a large telescope
of 25 cm or wider, cloud patterns, as well as some of the larger
satellites, such as Titania and Oberon, may be visible.
Size comparison of
Earth and Uranus
Diagram of the interior of Uranus
Uranus's mass is roughly 14.5 times that of Earth, making it the least
massive of the giant planets. Its diameter is slightly larger than
Neptune's at roughly four times that of Earth. A resulting density of
1.27 g/cm3 makes
Uranus the second least dense planet, after
Saturn. This value indicates that it is made primarily of
various ices, such as water, ammonia, and methane. The total mass
of ice in Uranus's interior is not precisely known, because different
figures emerge depending on the model chosen; it must be between
9.3 and 13.5
Hydrogen and helium
constitute only a small part of the total, with between 0.5 and
Earth masses. The remainder of the non-ice mass (0.5 to
Earth masses) is accounted for by rocky material.
The standard model of Uranus's structure is that it consists of three
layers: a rocky (silicate/iron–nickel) core in the centre, an icy
mantle in the middle and an outer gaseous hydrogen/helium
envelope. The core is relatively small, with a mass of only
Earth masses and a radius less than 20% of Uranus's; the
mantle comprises its bulk, with around 13.4
Earth masses, and the
upper atmosphere is relatively insubstantial, weighing about
Earth masses and extending for the last 20% of Uranus's
radius. Uranus's core density is around 9 g/cm3, with a
pressure in the centre of 8 million bars (800 GPa) and a
temperature of about 5000 K. The ice mantle is not in
fact composed of ice in the conventional sense, but of a hot and dense
fluid consisting of water, ammonia and other volatiles. This
fluid, which has a high electrical conductivity, is sometimes called a
The extreme pressure and temperature deep within
Uranus may break up
the methane molecules, with the carbon atoms condensing into crystals
of diamond that rain down through the mantle like
hailstones. Very-high-pressure experiments at the Lawrence
Livermore National Laboratory suggest that the base of the mantle may
comprise an ocean of liquid diamond, with floating solid
The bulk compositions of
Neptune are different from those
Jupiter and Saturn, with ice dominating over gases, hence
justifying their separate classification as ice giants. There may be a
layer of ionic water where the water molecules break down into a soup
of hydrogen and oxygen ions, and deeper down superionic water in which
the oxygen crystallises but the hydrogen ions move freely within the
Although the model considered above is reasonably standard, it is not
unique; other models also satisfy observations. For instance, if
substantial amounts of hydrogen and rocky material are mixed in the
ice mantle, the total mass of ices in the interior will be lower, and,
correspondingly, the total mass of rocks and hydrogen will be higher.
Presently available data does not allow a scientific determination
which model is correct. The fluid interior structure of Uranus
means that it has no solid surface. The gaseous atmosphere gradually
transitions into the internal liquid layers. For the sake of
convenience, a revolving oblate spheroid set at the point at which
atmospheric pressure equals 1 bar (100 kPa) is conditionally
designated as a "surface". It has equatorial and polar radii of
25,559 ± 4 km (15,881.6 ± 2.5 mi) and
24,973 ± 20 km (15,518 ± 12 mi),
respectively. This surface is used throughout this article as a
zero point for altitudes.
Uranus's internal heat appears markedly lower than that of the other
giant planets; in astronomical terms, it has a low thermal
flux. Why Uranus's internal temperature is so low is still not
understood. Neptune, which is Uranus's near twin in size and
composition, radiates 2.61 times as much energy into space as it
receives from the Sun, but
Uranus radiates hardly any excess heat
at all. The total power radiated by
Uranus in the far infrared (i.e.
heat) part of the spectrum is 7000106000000000000♠1.06±0.08 times
the solar energy absorbed in its atmosphere. Uranus's heat
flux is only 6998420000000000000♠0.042±0.047 W/m2, which is
lower than the internal heat flux of
Earth of about
6998750000000000000♠0.075 W/m2. The lowest temperature
recorded in Uranus's tropopause is 49 K (−224.2 °C;
−371.5 °F), making
Uranus the coldest planet in the Solar
One of the hypotheses for this discrepancy suggests that when Uranus
was hit by a supermassive impactor, which caused it to expel most of
its primordial heat, it was left with a depleted core temperature.
This impact hypothesis is also used in some attempts to explain the
planet's axial tilt. Another hypothesis is that some form of barrier
exists in Uranus's upper layers that prevents the core's heat from
reaching the surface. For example, convection may take place in a
set of compositionally different layers, which may inhibit the upward
heat transport; perhaps double diffusive convection is a
Atmosphere of Uranus
Although there is no well-defined solid surface within Uranus's
interior, the outermost part of Uranus's gaseous envelope that is
accessible to remote sensing is called its atmosphere.
Remote-sensing capability extends down to roughly 300 km below
the 1 bar (100 kPa) level, with a corresponding pressure
around 100 bar (10 MPa) and temperature of 320 K
(47 °C; 116 °F). The tenuous thermosphere extends over
two planetary radii from the nominal surface, which is defined to lie
at a pressure of 1 bar. The Uranian atmosphere can be divided into
three layers: the troposphere, between altitudes of −300 and
50 km (−186 and 31 mi) and pressures from 100 to
0.1 bar (10 MPa to 10 kPa); the stratosphere, spanning
altitudes between 50 and 4,000 km (31 and 2,485 mi) and
pressures of between 0.1 and 10−10 bar (10 kPa to
10 µPa); and the thermosphere extending from 4,000 km to as
high as 50,000 km from the surface. There is no mesosphere.
The composition of Uranus's atmosphere is different from its bulk,
consisting mainly of molecular hydrogen and helium. The helium
molar fraction, i.e. the number of helium atoms per molecule of gas,
is 6999150000000000000♠0.15±0.03 in the upper troposphere,
which corresponds to a mass fraction
6999260000000000000♠0.26±0.05. This value is close to the
protosolar helium mass fraction of
6999275000000000000♠0.275±0.01, indicating that helium has not
settled in its centre as it has in the gas giants. The
third-most-abundant component of Uranus's atmosphere is methane (CH
Methane has prominent absorption bands in the visible and
near-infrared (IR), making
Uranus aquamarine or cyan in colour.
Methane molecules account for 2.3% of the atmosphere by molar fraction
below the methane cloud deck at the pressure level of 1.3 bar
(130 kPa); this represents about 20 to 30 times the carbon
abundance found in the Sun. The mixing ratio[i] is much
lower in the upper atmosphere due to its extremely low temperature,
which lowers the saturation level and causes excess methane to freeze
out. The abundances of less volatile compounds such as ammonia,
water, and hydrogen sulfide in the deep atmosphere are poorly known.
They are probably also higher than solar values. Along with
methane, trace amounts of various hydrocarbons are found in the
stratosphere of Uranus, which are thought to be produced from methane
by photolysis induced by the solar ultraviolet (UV) radiation.
They include ethane (C
6), acetylene (C
2), methylacetylene (CH
2H), and diacetylene (C
2H). Spectroscopy has also uncovered traces of water
vapour, carbon monoxide and carbon dioxide in the upper atmosphere,
which can only originate from an external source such as infalling
dust and comets.
The troposphere is the lowest and densest part of the atmosphere and
is characterised by a decrease in temperature with altitude. The
temperature falls from about 320 K (47 °C; 116 °F) at
the base of the nominal troposphere at −300 km to 53 K
(−220 °C; −364 °F) at 50 km. The
temperatures in the coldest upper region of the troposphere (the
tropopause) actually vary in the range between 49 and 57 K
(−224 and −216 °C; −371 and −357 °F) depending on
planetary latitude. The tropopause region is responsible for
the vast majority of Uranus's thermal far infrared emissions, thus
determining its effective temperature of 59.1 ± 0.3 K
(−214.1 ± 0.3 °C;
−353.3 ± 0.5 °F).
The troposphere is thought to have a highly complex cloud structure;
water clouds are hypothesised to lie in the pressure range of 50 to
100 bar (5 to 10 MPa), ammonium hydrosulfide clouds in the
range of 20 to 40 bar (2 to 4 MPa), ammonia or hydrogen
sulfide clouds at between 3 and 10 bar (0.3 and 1 MPa) and
finally directly detected thin methane clouds at 1 to 2 bar (0.1
to 0.2 MPa). The troposphere is a dynamic part of
the atmosphere, exhibiting strong winds, bright clouds and seasonal
Uranus taken by the Space
Telescope Imaging Spectrograph
(STIS) installed on Hubble.
The middle layer of the Uranian atmosphere is the stratosphere, where
temperature generally increases with altitude from 53 K
(−220 °C; −364 °F) in the tropopause to between 800
and 850 K (527 and 577 °C; 980 and 1,070 °F) at the
base of the thermosphere. The heating of the stratosphere is
caused by absorption of solar UV and IR radiation by methane and other
hydrocarbons, which form in this part of the atmosphere as a
result of methane photolysis. Heat is also conducted from the hot
thermosphere. The hydrocarbons occupy a relatively narrow layer at
altitudes of between 100 and 300 km corresponding to a pressure
range of 10 to 0.1 mbar (10.00 to 0.10 hPa) and temperatures
of between 75 and 170 K (−198 and −103 °C; −325 and
−154 °F). The most abundant hydrocarbons are methane,
acetylene and ethane with mixing ratios of around 10−7 relative to
hydrogen. The mixing ratio of carbon monoxide is similar at these
altitudes. Heavier hydrocarbons and carbon dioxide have
mixing ratios three orders of magnitude lower. The abundance ratio
of water is around 7×10−9.
Ethane and acetylene tend to
condense in the colder lower part of stratosphere and tropopause
(below 10 mBar level) forming haze layers, which may be
partly responsible for the bland appearance of Uranus. The
concentration of hydrocarbons in the Uranian stratosphere above the
haze is significantly lower than in the stratospheres of the other
The outermost layer of the Uranian atmosphere is the thermosphere and
corona, which has a uniform temperature around 800 to
850 K. The heat sources necessary to sustain such a high
level are not understood, as neither the solar UV nor the auroral
activity can provide the necessary energy to maintain these
temperatures. The weak cooling efficiency due to the lack of
hydrocarbons in the stratosphere above 0.1 mBar pressure level
may contribute too. In addition to molecular hydrogen, the
thermosphere-corona contains many free hydrogen atoms. Their small
mass and high temperatures explain why the corona extends as far as
50,000 km (31,000 mi), or two Uranian radii, from its
surface. This extended corona is a unique feature of
Uranus. Its effects include a drag on small particles orbiting
Uranus, causing a general depletion of dust in the Uranian rings.
The Uranian thermosphere, together with the upper part of the
stratosphere, corresponds to the ionosphere of Uranus.
Observations show that the ionosphere occupies altitudes from 2,000 to
10,000 km (1,200 to 6,200 mi). The Uranian ionosphere is
denser than that of either
Saturn or Neptune, which may arise from the
low concentration of hydrocarbons in the stratosphere. The
ionosphere is mainly sustained by solar UV radiation and its density
depends on the solar activity.
Auroral activity is insignificant
as compared to
Jupiter and Saturn.
Temperature profile of the Uranian troposphere and lower stratosphere.
Cloud and haze layers are also indicated.
Zonal wind speeds on Uranus. Shaded areas show the southern collar and
its future northern counterpart. The red curve is a symmetrical fit to
The magnetic field of
Uranus as observed by
Voyager 2 in 1986. S and N
are magnetic south and north poles.
Before the arrival of Voyager 2, no measurements of the Uranian
magnetosphere had been taken, so its nature remained a mystery. Before
1986, scientists had expected the magnetic field of
Uranus to be in
line with the solar wind, because it would then align with Uranus's
poles that lie in the ecliptic.
Voyager's observations revealed that Uranus's magnetic field is
peculiar, both because it does not originate from its geometric
centre, and because it is tilted at 59° from the axis of
rotation. In fact the magnetic dipole is shifted from the
Uranus's centre towards the south rotational pole by as much as one
third of the planetary radius. This unusual geometry results in a
highly asymmetric magnetosphere, where the magnetic field strength on
the surface in the southern hemisphere can be as low as 0.1 gauss
(10 µT), whereas in the northern hemisphere it can be as high as
1.1 gauss (110 µT). The average field at the surface is
0.23 gauss (23 µT). Studies of
Voyager 2 data in 2017
suggest that this asymmetry causes Uranus's magnetosphere to connect
with the solar wind once a Uranian day, opening the planet to the
Sun's particles. In comparison, the magnetic field of
roughly as strong at either pole, and its "magnetic equator" is
roughly parallel with its geographical equator. The dipole moment
Uranus is 50 times that of Earth.
Neptune has a
similarly displaced and tilted magnetic field, suggesting that this
may be a common feature of ice giants. One hypothesis is that,
unlike the magnetic fields of the terrestrial and gas giants, which
are generated within their cores, the ice giants' magnetic fields are
generated by motion at relatively shallow depths, for instance, in the
water–ammonia ocean. Another possible explanation for the
magnetosphere's alignment is that there are oceans of liquid diamond
in Uranus's interior that would deter the magnetic field.
Despite its curious alignment, in other respects the Uranian
magnetosphere is like those of other planets: it has a bow shock at
about 23 Uranian radii ahead of it, a magnetopause at 18 Uranian
radii, a fully developed magnetotail, and radiation belts.
Overall, the structure of Uranus's magnetosphere is different from
Jupiter's and more similar to Saturn's. Uranus's magnetotail
trails behind it into space for millions of kilometres and is twisted
by its sideways rotation into a long corkscrew.
Uranus's magnetosphere contains charged particles: mainly protons and
electrons, with a small amount of H2+ ions. No heavier ions
have been detected. Many of these particles probably derive from the
thermosphere. The ion and electron energies can be as high as 4
and 1.2 megaelectronvolts, respectively. The density of
low-energy (below 1 kiloelectronvolt) ions in the inner
magnetosphere is about 2 cm−3. The particle population is
strongly affected by the Uranian moons, which sweep through the
magnetosphere, leaving noticeable gaps. The particle flux is high
enough to cause darkening or space weathering of their surfaces on an
astronomically rapid timescale of 100,000 years. This may be
the cause of the uniformly dark colouration of the Uranian satellites
Uranus has relatively well developed aurorae, which are
seen as bright arcs around both magnetic poles. Unlike Jupiter's,
Uranus's aurorae seem to be insignificant for the energy balance of
the planetary thermosphere.
Main article: Climate of Uranus
Uranus's southern hemisphere in approximate natural colour (left) and
in shorter wavelengths (right), showing its faint cloud bands and
atmospheric "hood" as seen by Voyager 2
At ultraviolet and visible wavelengths, Uranus's atmosphere is bland
in comparison to the other giant planets, even to Neptune, which it
otherwise closely resembles. When
Voyager 2 flew by
1986, it observed a total of ten cloud features across the entire
planet. One proposed explanation for this dearth of features
is that Uranus's internal heat appears markedly lower than that of the
other giant planets. The lowest temperature recorded in Uranus's
tropopause is 49 K (−224 °C; −371 °F), making
Uranus the coldest planet in the Solar System.
Banded structure, winds and clouds
Voyager 2 found that the visible southern hemisphere of
Uranus can be subdivided into two regions: a bright polar cap and dark
equatorial bands. Their boundary is located at about −45° of
latitude. A narrow band straddling the latitudinal range from −45 to
−50° is the brightest large feature on its visible surface.
It is called a southern "collar". The cap and collar are thought to be
a dense region of methane clouds located within the pressure range of
1.3 to 2 bar (see above). Besides the large-scale banded
structure, Voyager 2 observed ten small bright clouds, most lying
several degrees to the north from the collar. In all other
Uranus looked like a dynamically dead planet in 1986.
Voyager 2 arrived during the height of Uranus's southern summer
and could not observe the northern hemisphere. At the beginning of the
21st century, when the northern polar region came into view, the
Telescope (HST) and Keck telescope initially observed
neither a collar nor a polar cap in the northern hemisphere. So
Uranus appeared to be asymmetric: bright near the south pole and
uniformly dark in the region north of the southern collar. In
Uranus passed its equinox, the southern collar almost
disappeared, and a faint northern collar emerged near 45° of
The first dark spot observed on Uranus. Image obtained by the HST ACS
In the 1990s, the number of the observed bright cloud features grew
considerably partly because new high-resolution imaging techniques
became available. Most were found in the northern hemisphere as it
started to become visible. An early explanation—that bright
clouds are easier to identify in its dark part, whereas in the
southern hemisphere the bright collar masks them – was shown to be
incorrect. Nevertheless there are differences between the
clouds of each hemisphere. The northern clouds are smaller, sharper
and brighter. They appear to lie at a higher altitude. The
lifetime of clouds spans several orders of magnitude. Some small
clouds live for hours; at least one southern cloud may have persisted
Voyager 2 flyby. Recent observation also discovered
that cloud features on
Uranus have a lot in common with those on
Neptune. For example, the dark spots common on
Neptune had never
been observed on
Uranus before 2006, when the first such feature
Uranus Dark Spot
Uranus Dark Spot was imaged. The speculation is that
Uranus is becoming more Neptune-like during its equinoctial
The tracking of numerous cloud features allowed determination of zonal
winds blowing in the upper troposphere of Uranus. At the equator
winds are retrograde, which means that they blow in the reverse
direction to the planetary rotation. Their speeds are from −360 to
−180 km/h (−220 to −110 mph). Wind speeds
increase with the distance from the equator, reaching zero values near
±20° latitude, where the troposphere's temperature minimum is
located. Closer to the poles, the winds shift to a prograde
direction, flowing with Uranus's rotation. Wind speeds continue to
increase reaching maxima at ±60° latitude before falling to zero at
the poles. Wind speeds at −40° latitude range from 540 to
720 km/h (340 to 450 mph). Because the collar obscures all
clouds below that parallel, speeds between it and the southern pole
are impossible to measure. In contrast, in the northern hemisphere
maximum speeds as high as 860 km/h (540 mph) are observed
near +50° latitude.
Uranus in 2005. Rings, southern collar and a bright cloud in the
northern hemisphere are visible (HST ACS image).
For a short period from March to May 2004, large clouds appeared in
the Uranian atmosphere, giving it a Neptune-like appearance.
Observations included record-breaking wind speeds of 820 km/h
(510 mph) and a persistent thunderstorm referred to as "Fourth of
July fireworks". On 23 August 2006, researchers at the Space
Science Institute (Boulder, Colorado) and the University of Wisconsin
observed a dark spot on Uranus's surface, giving scientists more
insight into Uranus's atmospheric activity. Why this sudden
upsurge in activity occurred is not fully known, but it appears that
Uranus's extreme axial tilt results in extreme seasonal variations in
its weather. Determining the nature of this seasonal
variation is difficult because good data on Uranus's atmosphere have
existed for less than 84 years, or one full Uranian year. Photometry
over the course of half a Uranian year (beginning in the 1950s) has
shown regular variation in the brightness in two spectral bands, with
maxima occurring at the solstices and minima occurring at the
equinoxes. A similar periodic variation, with maxima at the
solstices, has been noted in microwave measurements of the deep
troposphere begun in the 1960s. Stratospheric temperature
measurements beginning in the 1970s also showed maximum values near
the 1986 solstice. The majority of this variability is thought to
occur owing to changes in the viewing geometry.
There are some indications that physical seasonal changes are
happening in Uranus. Although
Uranus is known to have a bright south
polar region, the north pole is fairly dim, which is incompatible with
the model of the seasonal change outlined above. During its
previous northern solstice in 1944,
Uranus displayed elevated levels
of brightness, which suggests that the north pole was not always so
dim. This information implies that the visible pole brightens
some time before the solstice and darkens after the equinox.
Detailed analysis of the visible and microwave data revealed that the
periodical changes of brightness are not completely symmetrical around
the solstices, which also indicates a change in the meridional albedo
patterns. In the 1990s, as
Uranus moved away from its solstice,
Hubble and ground-based telescopes revealed that the south polar cap
darkened noticeably (except the southern collar, which remained
bright), whereas the northern hemisphere demonstrated increasing
activity, such as cloud formations and stronger winds, bolstering
expectations that it should brighten soon. This indeed happened
in 2007 when it passed an equinox: a faint northern polar collar
arose, and the southern collar became nearly invisible, although the
zonal wind profile remained slightly asymmetric, with northern winds
being somewhat slower than southern.
The mechanism of these physical changes is still not clear. Near
the summer and winter solstices, Uranus's hemispheres lie alternately
either in full glare of the Sun's rays or facing deep space. The
brightening of the sunlit hemisphere is thought to result from the
local thickening of the methane clouds and haze layers located in the
troposphere. The bright collar at −45° latitude is also
connected with methane clouds. Other changes in the southern
polar region can be explained by changes in the lower cloud
layers. The variation of the microwave emission from
probably caused by changes in the deep tropospheric circulation,
because thick polar clouds and haze may inhibit convection. Now
that the spring and autumn equinoxes are arriving on Uranus, the
dynamics are changing and convection can occur again.
Main article: Formation and evolution of the Solar System
For details of the evolution of Uranus's orbit, see Nice model.
Many argue that the differences between the ice giants and the gas
giants extend to their formation. The
Solar System is
hypothesised to have formed from a giant rotating ball of gas and dust
known as the presolar nebula. Much of the nebula's gas, primarily
hydrogen and helium, formed the Sun, and the dust grains collected
together to form the first protoplanets. As the planets grew, some of
them eventually accreted enough matter for their gravity to hold on to
the nebula's leftover gas. The more gas they held onto, the
larger they became; the larger they became, the more gas they held
onto until a critical point was reached, and their size began to
increase exponentially. The ice giants, with only a few
of nebular gas, never reached that critical point.
Recent simulations of planetary migration have suggested that both ice
giants formed closer to the
Sun than their present positions, and
moved outwards after formation (the Nice model).
Main article: Moons of Uranus
See also: Timeline of discovery of
Solar System planets and their
Major moons of
Uranus in order of increasing distance (left to right),
at their proper relative sizes and albedos (collage of Voyager 2
Uranus System (NACO/VLT image)
Uranus has 27 known natural satellites. The names of these
satellites are chosen from characters in the works of
Alexander Pope. The five main satellites are Miranda, Ariel,
Umbriel, Titania, and Oberon. 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's
satellites, Titania, has a radius of only 788.9 km
(490.2 mi), 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's 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
Among the Uranian satellites, Ariel appears to have the youngest
surface with the fewest impact craters and Umbriel's the
oldest. Miranda has fault canyons 20 km (12 mi)
deep, terraced layers, and a chaotic variation in surface ages and
features. Miranda's past geologic activity is thought to have been
driven by tidal heating at a time when its orbit was more eccentric
than currently, probably as a result of a former 3:1 orbital resonance
with Umbriel. Extensional processes associated with upwelling
diapirs are the likely origin of Miranda's 'racetrack'-like
coronae. Ariel is thought to have once been held in a 4:1
resonance with Titania.
Uranus has at least one horseshoe orbiter occupying the Sun–Uranus
L3 Lagrangian point—a gravitationally unstable region at 180° in
its orbit, 83982 Crantor. Crantor moves inside Uranus's
co-orbital region on a complex, temporary horseshoe orbit. 2010 EU65
is also a promising
Uranus horseshoe librator candidate.
Main article: Rings of Uranus
The Uranian rings are composed of extremely dark particles, which vary
in size from micrometres to a fraction of a metre. Thirteen
distinct rings are presently known, the brightest being the ε ring.
All except two rings of
Uranus are extremely narrow – they are
usually a few kilometres wide. The rings are probably quite young; the
dynamics considerations indicate that they did not form with Uranus.
The matter in the rings may once have been part of a moon (or moons)
that was shattered by high-speed impacts. From numerous pieces of
debris that formed as a result of those impacts, only a few particles
survived, in stable zones corresponding to the locations of the
William Herschel described a possible ring around
Uranus in 1789. This
sighting is generally considered doubtful, because the rings are quite
faint, and in the two following centuries none were noted by other
observers. Still, Herschel made an accurate description of the epsilon
ring's size, its angle relative to Earth, its red colour, and its
apparent changes as
Uranus travelled around the Sun. The
ring system was definitively discovered on 10 March 1977 by James L.
Elliot, Edward W. Dunham, and
Jessica Mink using the Kuiper Airborne
Observatory. The discovery was serendipitous; they planned to use the
occultation of the star SAO 158687 (also known as HD 128598) by Uranus
to study its atmosphere. When their observations were analysed, they
found that the star had disappeared briefly from view five times both
before and after it disappeared behind Uranus. They concluded that
there must be a ring system around Uranus. Later they detected
four additional rings. The rings were directly imaged when
Voyager 2 passed
Uranus in 1986. Voyager 2 also
discovered two additional faint rings, bringing the total number to
In December 2005, the Hubble Space
Telescope detected a pair of
previously unknown rings. The largest is located twice as far from
Uranus as the previously known rings. These new rings are so far from
Uranus that they are called the "outer" ring system. Hubble also
spotted two small satellites, one of which, Mab, shares its orbit with
the outermost newly discovered ring. The new rings bring the total
number of Uranian rings to 13. In April 2006, images of the new
rings from the
Keck Observatory yielded the colours of the outer
rings: the outermost is blue and the other one red. One
hypothesis concerning the outer ring's blue colour is that it is
composed of minute particles of water ice from the surface of Mab that
are small enough to scatter blue light. In contrast,
Uranus's inner rings appear grey.
Animation about the discovering occultation in 1977. (Click on it to
Uranus has a complicated planetary ring system, which was the second
such system to be discovered in the
Solar System after Saturn's.
Uranus's aurorae against its equatorial rings, imaged by the Hubble
telescope. Unlike the aurorae of
Earth and Jupiter, those of Uranus
are not in line with its poles, due to its lopsided magnetic field.
Main article: Exploration of Uranus
Uranus as imaged by
Voyager 2 while en route to Neptune
In 1986, NASA's
Voyager 2 interplanetary probe encountered Uranus.
This flyby remains the only investigation of
Uranus carried out from a
short distance and no other visits are planned. Launched in 1977,
Voyager 2 made its closest approach to
Uranus on 24 January 1986,
coming within 81,500 km (50,600 mi) of the cloudtops, before
continuing its journey to Neptune. The spacecraft studied the
structure and chemical composition of Uranus's atmosphere,
including its unique weather, caused by its axial tilt of 97.77°. It
made the first detailed investigations of its five largest moons and
discovered 10 new ones. It examined all nine of the system's known
rings and discovered two more. It also studied the
magnetic field, its irregular structure, its tilt and its unique
corkscrew magnetotail caused by Uranus's sideways orientation.
Voyager 1 was unable to visit
Uranus because investigation of Saturn's
moon Titan was considered a priority. This trajectory took Voyager 1
out of the plane of the ecliptic, ending its planetary science
The possibility of sending the Cassini spacecraft from
Uranus was evaluated during a mission extension planning phase in
2009, but was ultimately rejected in favour of destroying it in the
Saturnian atmosphere. It would have taken about twenty years to
get to the Uranian system after departing Saturn. A Uranus
orbiter and probe was recommended by the 2013–2022 Planetary Science
Decadal Survey published in 2011; the proposal envisages launch during
2020–2023 and a 13-year cruise to Uranus. A
Uranus entry probe
Pioneer Venus Multiprobe
Pioneer Venus Multiprobe heritage and descend to 1–5
atmospheres. The ESA evaluated a "medium-class" mission called
Uranus Pathfinder. A New Frontiers
Uranus Orbiter has been
evaluated and recommended in the study, The Case for a Uranus
Orbiter. Such a mission is aided by the ease with which a
relatively big mass can be sent to the system—over 1500 kg with
an Atlas 521 and 12-year journey. For more concepts see Proposed
In astrology, the planet
Uranus () is the ruling planet of Aquarius.
Uranus is cyan and
Uranus is associated with electricity, the
colour electric blue, which is close to cyan, is associated with the
sign Aquarius (see
Uranus in astrology).
The chemical element uranium, discovered in 1789 by the German chemist
Martin Heinrich Klaproth, was named after the newly discovered planet
"Uranus, the Magician" is a movement in Gustav Holst's orchestral
suite The Planets, written between 1914 and 1916.
Operation Uranus was the successful military operation in World War II
Soviet army to take back
Stalingrad and marked the turning
point in the land war against the Wehrmacht.
The lines "Then felt I like some watcher of the skies/When a new
planet swims into his ken", from John Keats's "On First Looking Into
Chapman's Homer", are a reference to Herschel's discovery of
Many references to
Uranus in popular culture and news involve humor
about one pronunciation of its name resembling that of the phrase
Solar System portal
Book: Solar System
Outline of Uranus
2011 QF99 and 2014 YX49, the only two known
Colonisation of Uranus
Uranus in astrology
Uranus in fiction
Extraterrestrial diamonds (thought to be abundant in Uranus)
^ These are the mean elements from VSOP87, together with derived
^ a b c d e f g Refers to the level of 1 bar atmospheric pressure.
^ Calculated using data from Seidelmann, 2007.
^ Based on the volume within the level of 1 bar atmospheric pressure.
^ Calculation of He, H2 and CH4 molar fractions is based on a 2.3%
mixing ratio of methane to hydrogen and the 15/85 He/H2 proportions
measured at the tropopause.
^ Because, in the English-speaking world, the latter sounds like "your
anus", the former pronunciation also saves embarrassment: as Pamela
Gay, an astronomer at Southern Illinois University Edwardsville, noted
on her podcast, to avoid "being made fun of by any small
schoolchildren ... when in doubt, don't emphasise anything and
just say /ˈjʊərənəs/. And then run, quickly."
^ Cf. (not supported by all fonts)
^ Cf. (not supported by all fonts)
Mixing ratio is defined as the number of molecules of a compound per
a molecule of hydrogen.
^ a b "Uranus". Oxford English Dictionary (2 ed.). 1989.
^ a b The BBC Pronunciation Unit notes that /ˈjʊərənəs/ "is the
preferred usage of astronomers": Olausson, Lena; Sangster, Catherine
(2006). The Oxford BBC Guide to Pronunciation. Oxford, England: Oxford
University Press. p. 404. ISBN 978-0-19-280710-6.
^ a b c Munsell, Kirk (14 May 2007). "NASA:
Solar System Exploration:
Planets: Uranus: Facts & Figures". NASA. Retrieved 13 August
^ Seligman, Courtney. "Rotation Period and Day Length". Retrieved 13
^ a b c d e f g h i j k l Williams, Dr. David R. (31 January 2005).
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^ "The MeanPlane (Invariable plane) of the
Solar System passing
through the barycenter". 3 April 2009. Archived from the original on
14 May 2009. Retrieved 10 April 2009. (produced with Solex 10
Archived 29 April 2009 at
WebCite written by Aldo Vitagliano; see also
^ Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.;
Francou, G.; Laskar, J. (February 1994). "Numerical expressions for
precession formulae and mean elements for the
Moon and planets".
Astronomy and Astrophysics. 282 (2): 663–683.
^ a b c d e f g h i Seidelmann, P. Kenneth; Archinal, Brent A.;
A'Hearn, Michael F.; et al. (2007). "Report of the IAU/IAG Working
Group on cartographic coordinates and rotational elements: 2006".
Celestial Mechanics and Dynamical Astronomy. 98 (3): 155–180.
^ a b c Jacobson, R. A.; Campbell, J. K.; Taylor, A. H.; Synnott, S.
P. (June 1992). "The masses of
Uranus and its major satellites from
Voyager tracking data and earth-based Uranian satellite data". The
Astronomical Journal. 103 (6): 2068–2078.
^ de Pater, Imke; Lissauer, Jack J. (2015). Planetary Sciences (2nd
updated ed.). New York: Cambridge University Press. p. 250.
^ a b c d e f g h i j k l Podolak, M.; Weizman, A.; Marley, M.
(December 1995). "Comparative models of
Uranus and Neptune". Planetary
and Space Science. 43 (12): 1517–1522.
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(September 1993). "The Atmospheres of
Uranus and Neptune". Annual
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1995–2006". NASA. Archived from the original on 26 June 2007.
Retrieved 14 June 2007.
^ a b c Lindal, G. F.; Lyons, J. R.; Sweetnam, D. N.; Eshleman, V. R.;
Hinson, D. P.; Tyler, G. L. (30 December 1987). "The
Uranus: Results of Radio
Occultation Measurements with Voyager 2".
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Helium Abundance of
Uranus from Voyager Measurements".
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Bliss, D.; Boyce, J. M.; Brahic, A.; Briggs, G. A.; Brown, R. H.;
Collins, S. A. (4 July 1986). "
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2005). "Dynamics of cloud features on Uranus". Icarus. 179 (2):
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^ Herschel, William; Watson, Dr. (1781). "Account of a Comet, By Mr.
Herschel, F. R. S.; Communicated by Dr. Watson, Jun. of Bath, F. R.
S". Philosophical Transactions of the
Royal Society of London. 71:
^ a b c Journal of the
Royal Society and Royal Astronomical Society 1,
30, quoted in Miner, p. 8.
^ Royal Astronomical Society MSS W.2/1.2, 23; quoted in Miner p. 8.
^ RAS MSS Herschel W.2/1.2, 24, quoted in Miner p. 8.
^ RAS MSS Herschel W1/13.M, 14 quoted in Miner p. 8.
^ a b Lexell, A. J. (1787). "Recherches sur la nouvelle Planète,
découverte par M. Herschel & nommée par lui Georgium
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quoted in Miner, p. 11.
^ Miner, p. 11.
^ a b Dreyer, J. L. E. (1912). The Scientific Papers of Sir William
Royal Society and Royal Astronomical Society.
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^ a b Miner, p. 12
^ "Uranian, a.2 and n.1". Oxford English Dictionary (2 ed.).
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^ RAS MSS Herschel W.1/12.M, 20, quoted in Miner, p. 12
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^ a b c Bode 1784, pp. 88–90: [In original German]: "Bereits in
der am 12ten März 1782 bei der hiesigen naturforschenden Gesellschaft
vorgelesenen Abhandlung, habe ich den Namen des Vaters vom Saturn,
nemlich Uranos, oder wie er mit der lateinischen Endung gewöhnlicher
Uranus vorgeschlagen, und habe seit dem das Vergnügen gehabt,
daß verschiedene Astronomen und Mathematiker in ihren Schriften oder
in Briefen an mich, diese Benennung aufgenommen oder gebilligt. Meines
Erachtens muß man bei dieser Wahl die Mythologie befolgen, aus
welcher die uralten Namen der übrigen Planeten entlehnen worden; denn
in der Reihe der bisher bekannten, würde der von einer merkwürdigen
Person oder Begebenheit der neuern Zeit wahrgenommene Name eines
Planeten sehr auffallen. Diodor von Cicilien erzahlt die Geschichte
der Atlanten, eines uralten Volks, welches eine der fruchtbarsten
Gegenden in Africa bewohnte, und die Meeresküsten seines Landes als
das Vaterland der Götter ansah.
Uranus war ihr, erster König,
Stifter ihres gesitteter Lebens und Erfinder vieler nützlichen
Künste. Zugleich wird er auch als ein fleißiger und geschickter
Himmelsforscher des Alterthums beschrieben... Noch mehr:
der Vater des Saturns und des Atlas, so wie der erstere der Vater des
Jupiters."; [Translated]: "Already in the pre-read at the local
Natural History Society on 12th March 1782 treatise, I have the
father's name from Saturn, namely Uranus, or as it is usually with the
Latin suffix, proposed Uranus, and have since had the pleasure that
various astronomers and mathematicians, cited in their writings or
letters to me approving this designation. In my view, it is necessary
to follow the mythology in this election, which had been borrowed from
the ancient name of the other planets; because in the series of
previously known, perceived by a strange person or event of modern
times name of a planet would very noticeable. Diodorus of Cilicia
tells the story of Atlas, an ancient people that inhabited one of the
most fertile areas in Africa, and looked at the sea shores of his
country as the homeland of the gods.
Uranus was her first king,
founder of their civilized life and inventor of many useful arts. At
the same time he is also described as a diligent and skilful
astronomers of antiquity ... even more:
Uranus was the father of
Saturn and the Atlas, as the former is the father of Jupiter."
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1998) p 271. From the 1841 aphelion to the 2092 one, perihelia are
always 18.28 and aphelia always 20.10 astronomical units
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Cloud In The
Atmosphere Of Uranus".
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