Uranus

 
 

Uranus

 

 

Click on the images for larger ones below

 

While surveying the skies on a March evening in 1781, English astronomer Sir William Herschel discovered the planet Click here for larger imageUranus, at first mistaking it for a comet. After observing Uranus' path among the stars, astronomers determined that Uranus' orbit extends 19 times farther from the Sun than Earth's orbit. Although the diameter of the planet is four times greater than that of Earth, at this distance it appears in the sky as a faint disk spanning one thousandth of a degree, making it barely visible to the unaided eye only on clear, dark nights.

Early astronomers observed that the orbits of the four then-known Uranian moons were tipped 98 degrees relative to the planet's orbit around the Sun. These satellites, as well as Miranda (a Uranian moon discovered in 1948), and 10 small inner moons discovered by Voyager 2 in 1986 (bringing the total number of Uranian moons to 15), all lie in Uranus' equatorial plane. Several more Uranian moons were discovered in 2003 bringing the total number of Uranian mooms to 27.

Tipped Uranus behaves as a giant top as it spins on an axis almost in the plane of the orbit. This motion leads to extreme seasonal variation in what sunlight is available. Over the period of I Uranian year (84 Earth years), the polar regions of the planet go through four seasons, as on Earth, with perpetual sunlight in the summer, and total darkness in the winter. Periods of alternating day and night are interspersed in the spring and fall.

Click here for larger imageWith winters and summers extending for 21 Earth years, it would seem that Uranus should experience drastic temperature changes, but this is not the case. Uranus is so far from the Sun that its energy input per area is 360 times less than that on Earth; thus, little heating occurs during the summer. The rate of heat loss depends on the temperature of the region that is exposed to space; low cloud temperature leads to little heat loss during the winter. Despite Uranus' strange seasons, the temperature of the clouds shrouding the planet remain somewhat constant at -220 ~C.

Only one spacecraft has observed Uranus at close range Voyager 2. The Voyager spacecraft revealed that recurring patterns in radio signals from the planet indicated a rotation period (length of day) of 17.3 hours. Voyager scientists also discovered that, while the strength of Uranus' magnetic field is similar to Earth's, the Uranian poles are an amazing 60 degrees away from the rotational pole.

When Voyager 2 flew by the planet, the spacecraft's cameras revealed an almost featureless atmosphere; however, faint cloud markings between 20 and 50 !S latitude were recorded. The rotation rate of these clouds compared with the rotation of the magnetic field indicated wind speeds of 100-600 km/hr, which, unlike the winds of Jupiter and Saturn, blow westward.

Click here for larger imageIn 1977, Uranus was observed passing in front of a star. During this observation, it was revealed that Uranus possesses a system of at least 11 thin, widely, separated rings. In 1986, Voyager 2 confirmed the rings' existence.

Radio measurements showed the outermost ring, the epsilon, to be composed mostly of ice boulders several feet across. However, a very tenuous distribution of fine dust also seems to be spread throughout the ring system.

Incomplete rings and the varying opacity in several of the main rings leads scientists to believe that the ring system may be relatively young and did not form at the same time as Uranus. The particles that make up the rings may be remnants of a moon that was broken by a high-velocity impact or torn up by gravitational effects.

Today, we know that the dimly lit Uranian system consists of a planet surrounded by a flat system of rings and satellites. Bits of debris are concentrated into thin rings that orbit the planet between 1.4 and 2.0 Uranian radii, with the tiny moon Cordelia orbiting inside the brightest, outermost ring. Nine other small moons orbit from 2.1 to 3.4 Uranian radii. The five outer moons, with diameters ranging from 13 to 15 percent the size of our Moon, revolve around the planet at distances from 4 to 15 radii, or one-third to one-and-a-half times the distance between Earth and our Moon. Voyager 2 revealed that a remarkable variety of surface features mark these larger satellites, including craters, fractures, and frozen water.

Because no missions are currently being planned to return to Uranus, future information will need to be gained using ground-based or Earth-orbiting facilities.

 

 

Fast Facts

Distance from Sun

2.871 Billion Kilometers

Period of Revolution
(1 Uranian Year)

84.01 Earth Years

Equatorial Diameter

51,118 Kilometers

Atmosphere
(Main components)

Hydrogen and Helium

Moons

(15)In Ascending Distance from the Planet:
Cordelia, Ophelia, Bianca, Cressida,
Desdemona, Juliet, Portia, Rosalind,
Belinda, Puck, Miranda, Ariel,
Umbriel, Titania, Oberon

Several of Uranus' 27 known moons were discovered as recently as 2003. There may be more undiscovered moons out there.

Rings

11

Inclination of Orbit to Ecliptic

0.774 degrees

Eccentricity of Orbit

0.046

Rotation Period
(1Uranian Day)17 Hours 14 Minutes

 

Inclination of Axix

97.86 degrees



 

Uranus auroras glimpsed from Earth

Uranus' moons - Click Here13 April 2012
AGU Release No. 12-19
For Immediate Release

WASHINGTON—For the first time, scientists have captured images of auroras above the giant ice planet Uranus, finding further evidence of just how peculiar a world that distant planet is. Detected by means of carefully scheduled observations from the Hubble Space Telescope, the newly witnessed Uranian light show consisted of short-lived, faint, glowing dots – a world of difference from the colorful curtains of light that often ring Earth's poles.

In the new observations, which are the first to glimpse the Uranian aurora with an Earth-based telescope, the researchers detected the luminous spots twice on the dayside of Uranus – the side that’s visible from Hubble. Previously, the distant aurora had only been measured using instruments on a passing spacecraft. Unlike auroras on Earth, which can turn the sky Uranus Auroras - Click Heregreens and purples for hours, the newly detected auroras on Uranus appeared to only last a couple minutes.

In general, auroras are a feature of the magnetosphere, the area surrounding a planet that is controlled by its magnetic field and shaped by the solar wind, a steady flow of charged particles emanating from the sun. Auroras are produced in the atmosphere as charged solar wind particles accelerate in the magnetosphere and are guided by the magnetic field close to the magnetic poles – that’s why the Earthly auroras are found around high latitudes.

But contrary to the Earth – or even Jupiter and Saturn – “the magnetosphere of Uranus is very poorly known,” said Laurent Lamy, with the Observatoire de Paris in Meudon, Uranus - Click hereFrance, who led the new research.

The 2011 auroras differ not only from Earth’s auroras but also from the Uranian ones previously detected by Voyager 2. When that spacecraft made its flyby decades ago, Uranus was near its solstice – its rotational axis was pointed toward the Sun. In that configuration, the magnetic axis stayed at a large angle from the solar wind flow, producing a magnetosphere similar to the Earth’s magnetosphere, although more dynamic. Under those 1986 solstice conditions, the auroras lasted longer than the recently witnessed ones and were mainly seen on the nightside of the planet, similar to what’s observed on Earth, Lamy said. Hubble can’t see the far side of the planet, however, so researchers don’t know what types of auroras, if any, were generated there.

 

 

 

Hubble Spots Auroras on Uranus

April 10, 2017

 

This is a composite image of Uranus by Voyager 2 and two different observations made by Hubble — one for the ring and one for the auroras.

Click HereEver since Voyager 2 beamed home spectacular images of the planets in the 1980s, planet-lovers have been hooked on auroras on other planets. Auroras are caused by streams of charged particles like electrons that come from various origins such as solar winds, the planetary ionosphere, and moon volcanism. They become caught in powerful magnetic fields and are channeled into the upper atmosphere, where their interactions with gas particles, such as oxygen or nitrogen, set off spectacular bursts of light.

The auroras on Jupiter and Saturn are well-studied, but not much is known about the auroras of the giant ice planet Uranus. In 2011, the NASA/ESA Hubble Space Telescope became the first Earth-based telescope to snap an image of the auroras on Uranus. In 2012 and 2014 a team led by an astronomer from Paris Observatory took a second look at the auroras using the ultraviolet capabilities of the Space Telescope Imaging Spectrograph (STIS) installed on Hubble.

They tracked the interplanetary shocks caused by two powerful bursts of solar wind traveling from the sun to Uranus, then used Hubble to capture their effect on Uranus’ auroras — and found themselves observing the most intense auroras ever seen on the planet. By watching the auroras over time, they collected the first direct evidence that these powerful shimmering regions rotate with the planet. They also re-discovered Uranus’ long-lost magnetic poles, which were lost shortly after their discovery by Voyager 2 in 1986 due to uncertainties in measurements and the featureless planet surface.

 

 

Credit: ESA/Hubble & NASA, L. Lamy / Observatoire de Paris
Text credit: European Space Agency

 

 

 

 

 

Comparing Uranus To Earth

Size comparison of Earth and Uranus

 

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