Editing Uranus (section)

== Orbit and rotation ==
Uranus orbits the Sun once every 84 years. As viewed against the background of stars, since being discovered in 1781,<ref>{{Cite news |last=McKie |first=Robin |date=16 July 2022 |title=Journey to the mystery planet: why Uranus is the new target for space exploration |url=https://www.theguardian.com/science/2022/jul/16/uranus-mission-space-exploration-nasa |url-status=live |archive-url=https://web.archive.org/web/20240106022932/https://www.theguardian.com/science/2022/jul/16/uranus-mission-space-exploration-nasa |archive-date=6 January 2024 |access-date=28 April 2024 |work=The Observer |language=en-GB |issn=0029-7712}}</ref> the planet has returned to the point of its discovery northeast of the binary star [[Zeta Tauri]] twice—in March 1865 and March 1949—and will return to this location again in April 2033.<ref>{{Cite web |last=Fahad |first=Engr |date=26 December 2022 |title=Uranus Size and Uranus Distance from the Sun |url=https://www.electroniclinic.com/uranus-size-and-uranus-distance-from-the-sun/ |url-status=live |archive-url=https://web.archive.org/web/20230301094631/https://www.electroniclinic.com/uranus-size-and-uranus-distance-from-the-sun/ |archive-date=1 March 2023 |access-date=28 April 2024 |website=Electronic Clinic |language=en-US}}</ref>

Its average distance from the Sun is roughly {{convert|20|AU|e9km+e9mi|sigfig=1|abbr=unit|lk=on}}. 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 dwarf planet [[Pluto]].<ref name=AA>Jean Meeus, ''Astronomical Algorithms'' (Richmond, VA: Willmann-Bell, 1998) p 271. From the 1841 aphelion to the 2092 one, perihelia are always 18.28 and aphelia always 20.10 astronomical units</ref> The intensity of sunlight varies inversely with the square of the distance—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.<ref>{{cite web | title=Next Stop: Uranus | publisher=Astronomical Society of the Pacific | work=The Universe in the Classroom | url=https://astrosociety.org/file_download/inline/be6d544d-9619-4a20-9614-9f3d097fc32d | date=1986 | access-date=4 May 2021 | archive-date=4 May 2021 | archive-url=https://web.archive.org/web/20210504003407/https://astrosociety.org/file_download/inline/be6d544d-9619-4a20-9614-9f3d097fc32d | url-status=live }}</ref>

The orbital elements of Uranus were first calculated in 1783 by [[Pierre-Simon Laplace]].<ref name="georgeforbes" /> With time, discrepancies began to appear between 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 September 1846, [[Johann Gottfried Galle]] located a new planet, later named [[Neptune]], at nearly the position predicted by Le Verrier.<ref>{{cite web | title=Mathematical discovery of planets | last1=O'Connor | first1=J J. | last2=Robertson | first2=E. F. | website=MacTutor | name-list-style=amp | url=http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Neptune_and_Pluto.html | date=September 1996 | access-date=13 June 2007 | archive-date=20 August 2011 | archive-url=https://web.archive.org/web/20110820080638/http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Neptune_and_Pluto.html | url-status=live }}</ref>

The rotational period of the interior of Uranus is 17&nbsp;hours, 14&nbsp;minutes, and 52&nbsp;seconds<ref name="Lamy2025">{{cite journal |last1=Lamy |first1=L. |last2=Prangé |first2=R. |last3=Berthier |first3=J. |last4=Tao |first4=C. |last5=Kim |first5=T. |last6=Roth |first6=L. |last7=Barthélémy |first7=M. |last8=Chaufray |first8=J.-Y. |last9=Rymer |first9=A. |last10=Dunn |first10=W. R. |last11=Wibisono |first11=A. D. |last12=Melin |first12=H. |title=A new rotation period and longitude system for Uranus |journal=Nature Astronomy |date=7 April 2025 |pages=1–8 |doi=10.1038/s41550-025-02492-z |url=https://www.nature.com/articles/s41550-025-02492-z |language=en |issn=2397-3366}}</ref> which was determined by tracking the rotational motion of Uranus's aurorae.<ref>{{cite news |url=https://science.nasa.gov/missions/hubble/hubble-helps-determine-uranus-rotation-rate-with-unprecedented-precision/?utm_source=FBPAGE&utm_medium=NASA%27s+Hubble+Space+Telescope&utm_campaign=NASASocial&linkId=794640986&fbclid=IwY2xjawJjwbFleHRuA2FlbQIxMAABHtFT6KdfU0L0HFsadSMK22xZx4PCRt3vCs3qB5C9mUNKQOYUIWP_EjYeweQy_aem_qbiW_Oe3wOw9UvtY1f0FiA |title=Hubble Helps Determine Uranus' Rotation Rate with Unprecedented Precision |publisher=NASA Hubble Space Telescope imaging team|date=9 April 2025 |access-date=9 April 2025}}</ref> As on all [[giant planet]]s, 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 hours.<ref>{{Cite web |last1=Gierasch |first1=Peter J. |last2=Nicholson |first2=Philip D. |name-list-style=amp |date=2004 |title=Uranus |url=http://www.warrentboe.org/_files/TeacherPages/792/Uranus_Article.pdf |url-status=live |archive-url=https://web.archive.org/web/20150402112123/http://www.warrentboe.org/_files/TeacherPages/792/Uranus_Article.pdf |archive-date=2 April 2015 |access-date=8 March 2015 |website=World Book}}</ref>

=== Axial tilt ===
[[File:Uranus orientation 1985-2030.gif|thumb|Simulated Earth view of Uranus from 1986 to 2030, from southern summer solstice in 1986 to equinox in 2007 and northern summer solstice in 2028.]]
The Uranian axis of rotation is approximately parallel to the plane of the Solar System, with an [[axial tilt]] of 82.23°.<!-- To match the description on the page [[Axial tilt]], 82.23° and not 97.77° is used throughout this page. See the following explanation. --> Depending on which pole is considered north, the tilt can be described either as 82.23° or as 97.77°. The former follows the [[International Astronomical Union]] [[axial tilt|definition]] that the north pole is the pole which lies on Earth's North's side of the [[invariable plane]] of the [[Solar System]]. Uranus has [[Retrograde and prograde motion|retrograde]] rotation when defined this way. Alternatively, the convention in which a body's north and south poles are defined according to the [[right-hand rule]] in relation to the direction of rotation, Uranus's axial tilt may be given instead as 97.77°, which reverses which pole is considered north and which is considered south and giving the planet prograde rotation.<ref>{{cite web |url=http://roger.ecn.purdue.edu/~masl/documents/masl/coords.html |title=Coordinate Frames Used in MASL |date=2003 |access-date=13 June 2007 |archive-url=https://web.archive.org/web/20041204061125/http://roger.ecn.purdue.edu/~masl/documents/masl/coords.html <!--Added by H3llBot--> |archive-date=4 December 2004}}</ref> This gives it seasonal changes completely unlike those of the other planets. Pluto and asteroid [[2 Pallas]] also have extreme axial tilts. Near the [[solstice]], one pole faces the Sun continuously and the other faces away, with only a narrow strip around the equator experiencing a rapid day–night cycle, with the Sun low over the horizon. On the other side of Uranus's orbit, the orientation of the poles towards the Sun is reversed. Each pole gets around 42&nbsp;years of continuous sunlight, followed by 42&nbsp;years of darkness.<ref>{{Cite web |last=Sromovsky |first=Lawrence |date=2006 |title=Hubble captures rare, fleeting shadow on Uranus |url=http://www.news.wisc.edu/releases/12826.html |url-status=dead |archive-url=https://web.archive.org/web/20110720221646/http://www.news.wisc.edu/releases/12826.html |archive-date=20 July 2011 |access-date=9 June 2007 |website=University of Wisconsin Madison}}</ref> Near the time of the [[equinox]]es, the Sun faces the equator of Uranus, giving a period of day–night cycles similar to those seen on most of the other planets.

One result of this axis orientation is that, averaged over the Uranian year, the near-polar regions of Uranus receive a greater energy input from the 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 cause of 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.<ref>{{Cite book |title=Uranus |date=1991 |publisher=[[University of Arizona Press]] |isbn=978-0-8165-1208-9 |editor-last=Bergstralh |editor-first=Jay T. |location=Tucson |pages=485–486 |editor-last2=Miner |editor-first2=Ellis D. |editor-last3=Matthews |editor-first3=Mildred Shapley}}</ref> Research by Jacob Kegerreis of [[Durham University]] suggests that the tilt resulted from a rock larger than Earth crashing into the planet 3 to 4&nbsp;billion years ago.<ref>{{cite news |url=https://www.apnews.com/d1e2c440af57450ab82b62d035adac61 |title=Science Says: A big space crash likely made Uranus lopsided |work=[[Associated Press]] |last=Borenstein |first=Seth |date=21 December 2018 |access-date=17 January 2019 |archive-date=19 January 2019 |archive-url=https://web.archive.org/web/20190119121444/https://www.apnews.com/d1e2c440af57450ab82b62d035adac61 |url-status=live }}</ref> Uranus's south pole was pointed almost directly at the Sun at the time of ''Voyager&nbsp;2''{{'s}} flyby in 1986.<ref>{{cite journal |url=http://www.hnsky.org/iau-iag.htm |title=Report of the IAU/IAG working group on cartographic coordinates and rotational elements of the planets and satellites: 2000 |volume=82 |issue=1 |pages=83 |journal=Celestial Mechanics and Dynamical Astronomy |date=2000 |access-date=13 June 2007 |bibcode=2002CeMDA..82...83S |last1=Seidelmann |first1=P. K. |last2=Abalakin |first2=V. K. |last3=Bursa |first3=M. |last4=Davies |first4=M. E. |last5=De Bergh |first5=C. |last6=Lieske |first6=J. H. |last7=Oberst |first7=J. |last8=Simon |first8=J. L. |last9=Standish |first9=E. M. |last10=Stooke |first10=P. |last11=Thomas |first11=P. C. |doi=10.1023/A:1013939327465 |s2cid=189823009 |archive-date=12 May 2020 |archive-url=https://web.archive.org/web/20200512151452/http://www.hnsky.org/iau-iag.htm |url-status=dead |url-access=subscription }}</ref><ref>{{cite web |url=http://pds.jpl.nasa.gov/documents/sr/stdref_021015/Chapter02.pdf |title=Cartographic Standards |work=NASA |access-date=13 June 2007 |url-status=dead |archive-url=https://web.archive.org/web/20040407151631/http://pds.jpl.nasa.gov/documents/sr/stdref_021015/Chapter02.pdf |archive-date=7 April 2004 }}</ref>

{| class="wikitable" style="text-align: center; margin-left: 20px;"
|+List of solstices and equinoxes<ref>{{cite conference |last=Hammel |first=Heidi B. |date=5 September 2006 |title=Uranus nears Equinox |url=http://www.apl.ucl.ac.uk/iopw/uworkshop_060905.pdf |archive-url=https://web.archive.org/web/20090225084057/http://www.apl.ucl.ac.uk/iopw/uworkshop_060905.pdf |archive-date=25 February 2009 |book-title=A report from the 2006 Pasadena Workshop}}</ref>
|-
! Northern hemisphere
! Year
! Southern hemisphere
|-
| Winter solstice
| 1902, 1986, 2069
| Summer solstice
|-
| Vernal equinox
| 1923, 2007, 2092
| Autumnal equinox
|-
| Summer solstice
| 1944, 2028
| Winter solstice
|-
| Autumnal equinox
| 1965, 2050
| Vernal equinox
|}

=== Visibility from Earth ===
[[File:UranusAndMoon 20221108 fromJP (crop).jpg|thumb|Uranus seen through an amateur telescope, shortly after lunar [[occultation]], during the [[November 2022 lunar eclipse]]]]
The mean [[apparent magnitude]] of Uranus is 5.68 with a standard deviation of 0.17, while the extremes are 5.38 and 6.03.<ref name="Mallama_and_Hilton" /> This range of brightness is near the limit of [[naked eye]] visibility. Much of the variability is dependent upon the planetary latitudes being illuminated from the Sun and viewed from the Earth.<ref name="Schmude_et_al" /> Its [[angular diameter]] is between 3.4 and 3.7&nbsp;arcseconds, compared with 16 to 20&nbsp;arcseconds for Saturn and 32 to 45&nbsp;arcseconds for Jupiter.<ref name="ephemeris" /> At [[Opposition (astronomy)|opposition]], Uranus is visible to the naked eye in dark skies, and becomes an easy target even in urban conditions with binoculars.<ref name="fact" /> On larger amateur telescopes with an objective diameter of between 15 and 23&nbsp;cm, Uranus appears as a pale cyan disk with distinct [[limb darkening]]. With a large telescope of 25&nbsp;cm or wider, cloud patterns, as well as some of the larger satellites, such as [[Titania (moon)|Titania]] and [[Oberon (moon)|Oberon]], may be visible.<ref>{{Cite web |last=Nowak |first=Gary T. |date=2006 |title=Uranus: the Threshold Planet of 2006 |url=http://www.vtastro.org/Articles/uranus2006.html |archive-url=https://web.archive.org/web/20110727233304/http://www.vtastro.org/Articles/uranus2006.html |archive-date=27 July 2011 |access-date=14 June 2007 |website=Vtastro.org}}</ref>