What is Axial tilt?
[[File:AxialTiltObliquity.png|thumb|380px|Axial tilt of Earth is 23.439281°]] In [[astronomy]], '''axial tilt''' is the angle between a [[planet|planet's]] [[axis of rotation|rotational axis]] at its north pole and a line perpendicular to the [[Orbital plane (astronomy)|orbital plane]] of the planet. It is also called '''axial inclination''' or '''obliquity'''. The axial tilt of Earth is the cause of [[season]]s like summer and winter on Earth. == Axial tilt of bodies in the Solar System == {{double image|right|Globespin-tilt-23.4.gif|170|Right-hand grip rule.svg|150|To understand axial tilt, we employ the [[right-hand rule]]. When the fingers of the right hand are curled around in the direction of the planet's rotation, the thumb points in the direction of the north [[Geographical pole|pole]]}} *[[Sun]] 7.25 (to the [[Ecliptic]]) *[[Mercury (planet)|Mercury]] ~0.01 *[[Venus (planet)|Venus]] 177.4 *[[Earth]] 23.439281 *[[Moon]] 1.5424 *[[Mars (planet)|Mars]] 25.19 *[[Ceres (dwarf planet)|Ceres]] ~4 *[[Jupiter (planet)|Jupiter]] 3.13 *[[Saturn (planet)|Saturn]] 26.73 *[[Uranus (planet)|Uranus]] 97.77 *[[Neptune (planet)|Neptune]] 28.32 *[[Pluto (planet)|Pluto]] 119.61 ==Axial tilt of Venus, Uranus, Pluto== The axial tilts of Venus, Uranus and Pluto are greater than 90 degrees for the following reasons: * '''Venus''': Venus is rotating very slowly in a [[retrograde]] direction, opposite to the direction of planets like Earth. The north pole of Venus is pointed 'down' (southward); hence the angle between the rotational axis of Venus passing through its north pole and the line perpendicular to its orbital plane is 177.4 degrees. There are various theories as to why this is. Its rotation and lack of a moon may be explained by gigantic impacts early in its life.<ref>{{cite news|publisher=Scientific American |date=October 2006|title=Double impact may explain why Venus has no moon|author=Musser, George |url=http://www.sciam.com/article.cfm?articleID=0008DCD1-0A66-152C-8A6683414B7F0000&ref=sciam |access-date=2011-12-