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== Orbital characteristics ==

== Orbital characteristics ==

Uranus' average distance from the sun (semi-major axis) is 19.1 AU, which is close to the 19.6 AU predicted by the [[Titius-Bode law]]. Its sidereal year is 84.02 [[Earth]] years. The orbital excentricity is 0.046, which is nearly circular (though the orbit of Earth is more circular still). Uranus' orbit is very slightly inclined to the plane of the ecliptic; in fact its orbital inclination with respect to the ecliptic is the least of those of all the planets.

Uranus's average distance from the sun (semi-major axis) is 19.1 AU, which is close to the 19.6 AU predicted by the [[Titius-Bode law]]. Its sidereal year is 84.02 [[Earth]] years. The orbital excentricity is 0.046, which is nearly circular (though the orbit of Earth is more circular still). Uranus's orbit is very slightly inclined to the plane of the ecliptic; in fact its orbital inclination with respect to the ecliptic is the least of those of all the planets.

== Rotational characteristics ==

== Rotational characteristics ==

Uranus' sidereal day is 17.24 Earth hours. Uranus' rotation is ''retrograde'' with respect to its orbit around the Sun and the orbits of most of the other planets. Moreover its axis is tilted 97.86° with respect to its orbital plane, so that in a sense the planet is rolling on its side.

Uranus's sidereal day is 17.24 Earth hours. Uranus's rotation is ''retrograde'' with respect to its orbit around the Sun and the orbits of most of the other planets. Moreover its axis is tilted 97.86° with respect to its orbital plane, so that in a sense the planet is rolling on its side.

The planet has a magnetic field, whose axis is oriented 60° away from its rotational axis and, furthermore, does not intercept the planet's center.

The planet has a magnetic field, whose axis is oriented 60° away from its rotational axis and, furthermore, does not intercept the planet's center.

=== Atmosphere ===

=== Atmosphere ===

[[Voyager 2]] did not resolve many more features than can be seen through an ordinary earthbound telescope. But seven years of observation by the [[Hubble Space Telescope]] have shown that Uranus' atmosphere is quite active. It has even developed a visible storm (the dark spot), which Voyager 2 did not capture.

[[Voyager 2]] did not resolve many more features than can be seen through an ordinary earthbound telescope. But seven years of observation by the [[Hubble Space Telescope]] have shown that Uranus's atmosphere is quite active. It has even developed a visible storm (the dark spot), which Voyager 2 did not capture.

== Ring system ==

== Ring system ==

=== Orientation of the Uranian system ===

=== Orientation of the Uranian system ===

According to evolutionary theories of how the Solar System formed (i.e. the [[nebular hypothesis]]), Uranus' axis should not be tilted 98 degrees with respect to its orbit. Moreover its moons orbit Uranus around its equator, like the hands of a clock around a clock face. Uranus' thirteen rings also are around its equator, so they look vertical. The nebular hypothesis predicts none of these observations.

According to evolutionary theories of how the solar system formed (i.e., the [[nebular hypothesis]]), Uranus's axis should not be tilted 98 degrees with respect to its orbit. Moreover its moons orbit Uranus around its equator, like the hands of a clock around a clock face. Uranus' thirteen rings also are around its equator, so they look vertical. The nebular hypothesis predicts none of these observations.

Naturalistic [[Astronomy|astronomers]] theorize that Uranus originally formed upright, but suffered a collision with another object, producing its severe tilt. This, however, raises more questions:

Naturalistic [[Astronomy|astronomers]] theorize that Uranus originally formed upright, but suffered a collision with another object, producing its severe tilt. This, however, raises more questions:

# Why is its orbit less eccentric than those of all the other planets except only those of [[Venus]], [[Neptune]], and [[Earth]]?

# Why is its orbit less eccentric than those of all the other planets except only those of [[Venus]], [[Neptune]], and [[Earth]]?

# Why is Uranus' orbit less inclined to the ecliptic than is that of any planet except Earth?

# Why is Uranus's orbit less inclined to the ecliptic than is that of any planet except Earth?

# Why are the orbits of Uranus' moons so slightly inclined with respect to Uranus' present equator?<ref name=AiG>Psarris, Spike. "[http://www.answersingenesis.org/creation/v24/i3/uranus.asp Entry for Uranus]." ''Creation'', 24(3):38-40, June 2002. Now hosted by [[Answers in Genesis]]. Accessed April 25, 2008.</ref> Indeed, the vertical orientation of Uranus' moons and of some of its rings was already well-known to astronomers before the Voyager 2 flyby. If the moons formed before the collision, then another series of precisely timed collisions would have been required to change the azimuths of all the orbits, ''and'' the rings&mdash;an absurd violation of [[Occam's razor]]. And if they formed after the collision, then in the absence of any condensing gas cloud, they ought to be inclined at random.

# Why are the orbits of Uranus's moons so slightly inclined with respect to Uranus's present equator?<ref name=AiG>Psarris, Spike. "[http://www.answersingenesis.org/creation/v24/i3/uranus.asp Entry for Uranus]." ''Creation'', 24(3):38-40, June 2002. Now hosted by [[Answers in Genesis]]. Accessed April 25, 2008.</ref> Indeed, the vertical orientation of Uranus's moons and of some of its rings was already well-known to astronomers before the Voyager 2 flyby. If the moons formed before the collision, then another series of precisely timed collisions would have been required to change the azimuths of all the orbits, ''and'' the rings&mdash;an absurd violation of [[Occam's razor]]. And if they formed after the collision, then in the absence of any condensing gas cloud, they ought to be inclined at random.

Naturalists try to explain that last by suggesting that Uranus' moons are leftover debris from the collision that tilted its axis. However, Uranus' moons make up only one hundredth of one percent of the mass of the planet, and an impact violent enough to knock the giant over would have produced far more debris than that. (Earth's [[Moon]], also supposed to be the result of a giant collision involving its primary, has a mass of 1.23% that of earth.)<ref name=AiG/><ref name=Psarris>Psarris, Spike. ''Our Created Solar System'' Seattle Creation Conference, 2006.</ref> Moreover, not only are the moons of Uranus oriented well to Uranus' equator, but many of them orbit retrograde to Uranus' own rotation.

Naturalists try to explain that last by suggesting that Uranus's moons are leftover debris from the collision that tilted its axis. However, Uranus's moons make up only one hundredth of one percent of the mass of the planet, and an impact violent enough to knock the giant over would have produced far more debris than that. (Earth's [[Moon]], also supposed to be the result of a giant collision involving its primary, has a mass of 1.23% that of earth.)<ref name=AiG/><ref name=Psarris>Psarris, Spike. ''Our Created Solar System'' Seattle Creation Conference, 2006.</ref> Moreover, not only are the moons of Uranus oriented well to Uranus's equator, but many of them orbit retrograde to Uranus's own rotation.

=== The magnetic field ===

=== The magnetic field ===

As mentioned, Uranus' magnetic axis is 60 degrees displaced from Uranus' axis of rotation, and the axis also does not intercept the planet's center. Moreover the strength of Uranus' magnetic field presented another problem for the evolutionary model when Voyager 2 flew by the planet in 1986; however, it did not surprise creationists, as Dr. Russell Humphreys predicted its strength based on the creation model two years before Voyager flew by.<ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''Creation Research Society Quarterly'' 21(3), December 1984. Accessed April 29, 2008.</ref>

As mentioned, Uranus's magnetic axis is 60 degrees displaced from Uranus's axis of rotation, and the axis also does not intercept the planet's center. Moreover the strength of Uranus's magnetic field presented another problem for the evolutionary model when Voyager 2 flew by the planet in 1986; however, it did not surprise creationists, as Dr. Russell Humphreys predicted its strength based on the creation model two years before Voyager flew by.<ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''Creation Research Society Quarterly'' 21(3), December 1984. Accessed April 29, 2008.</ref>

=== Radiation of energy ===

=== Radiation of energy ===

The other three gas giants ([[Jupiter]], [[Saturn]], and [[Neptune]]) radiate more energy than they absorb from the Sun. Uranus does not. Yet Uranus and Neptune are of comparable size, mass, atmospheric composition, and length of the sidereal day. No naturalistic theory can account for this salient difference. Uranus' peculiar lack of an internal heat source was known before Voyager and confirmed by Voyager.<ref name=AiG/><ref name=Psarris/><ref name=Henry>Henry, Jonathan. "[http://www.answersingenesis.org/tj/v15/i3/uranus_energy.asp The energy balance of Uranus: implications for special creation]." ''Journal of Creation'' (formerly ''TJ''), 15(3):85-91, December, 2001. Hosted by [[Answers in Genesis]]. Accessed April 25, 2008.</ref>

The other three gas giants ([[Jupiter]], [[Saturn]], and [[Neptune]]) radiate more energy than they absorb from the Sun. Uranus does not. Yet Uranus and Neptune are of comparable size, mass, atmospheric composition, and length of the sidereal day. No naturalistic theory can account for this salient difference. Uranus's peculiar lack of an internal heat source was known before Voyager and confirmed by Voyager.<ref name=AiG/><ref name=Psarris/><ref name=Henry>Henry, Jonathan. "[http://www.answersingenesis.org/tj/v15/i3/uranus_energy.asp The energy balance of Uranus: implications for special creation]." ''Journal of Creation'' (formerly ''TJ''), 15(3):85-91, December, 2001. Hosted by [[Answers in Genesis]]. Accessed April 25, 2008.</ref>

== Satellites ==

== Satellites ==

Uranus has twenty-seven named satellites and a number of concentric rings. The orbits of its satellites are slightly inclined to Uranus' own equator. Remarkably, many of the revolutions of Uranus' moons are retrograde. Uranus' satellites include [[Miranda]], easily the most remarkable natural satellite in all the [[solar system]].

Uranus has twenty-seven named satellites and a number of concentric rings. The orbits of its satellites are slightly inclined to Uranus's own equator. Remarkably, many of the revolutions of Uranus's moons are retrograde. Uranus's satellites include [[Miranda]], easily the most remarkable natural satellite in all the [[solar system]].

== Missions to Uranus ==

== Missions to Uranus ==

The only deep-space probe to visit Uranus thus far has been [[Voyager 2]], which flew by Uranus on January 24, 1986. Voyager 2 discovered ten of Uranus' twenty-seven satellites, and two previously unknown rings. Voyager 2 then continued onward to [[Neptune]] before heading out of the [[solar system]].

The only deep-space probe to visit Uranus thus far has been [[Voyager 2]], which flew by Uranus on January 24, 1986. Voyager 2 discovered ten of Uranus's twenty-seven satellites, and two previously unknown rings. Voyager 2 then continued onward to [[Neptune]] before heading out of the [[solar system]].

== Gallery ==

== Gallery ==