The seventh planet from the Sun is Uranus. The Greek god of the sky Uranus (Caelus), who was the great-grandfather of Ares (Mars), the grandfather of Zeus (Jupiter), and the father of Cronus, is referenced in the name of the object (Saturn). In the Solar System, it possesses the fourth-largest planetary mass and the third-largest planetary radius. Neptune and Uranus share similarities in their bulk chemical compositions, which are different from those of Jupiter and Saturn, the two larger gas giants. To distinguish Uranus and Neptune from the other large planets, astronomers frequently label them as “ice giants.”
Ice giants, like gas giants, lack a distinct “solid surface.” The atmosphere of Uranus is mostly made of hydrogen and helium, like that of Jupiter and Saturn, but it also contains a greater amount of “ices” including water, ammonia, and methane as well as traces of other hydrocarbons. With a minimum temperature of 49 K (224 °C; 371 °F), it has the coldest planetary atmosphere in the Solar System. It also has a complex, layered cloud structure, with water thought to make up the lowest clouds and methane thought to make up the uppermost layer of clouds. Ices and rock make up the majority of Uranus’ interior.
Uranus has a magnetosphere, a ring system, and multiple moons, just like the other major planets. The axis of rotation of the Uranian system is slanted sideways, almost into the plane of its solar orbit, giving it a peculiar structure. Therefore, its north and south poles are located where the equator is on the majority of other planets. Images taken by Voyager 2 in 1986 revealed Uranus to be an almost featureless planet in visible light, devoid of the cloud bands or storms found on the other large planets. The only spacecraft to have ever visited the planet is Voyager 2. As Uranus reached its equinox in 2007, observations from Earth revealed seasonal shifts and increased weather activity. Winds can travel at much to 250 m/s (900 km/h; 560 mph).
With an axial tilt of 97.77°, the axis of rotation of Uranus is roughly parallel to the plane of the solar system (as defined by prograde rotation). Due to this, it has seasonal variations that are entirely different from those of other worlds. Only a small area surrounding the equator has a quick day-night cycle, with the Sun low above the horizon, as both poles face the Sun continuously in the vicinity of the solstice. The poles’ direction towards the Sun is reversed on the other side of Uranus’ orbit. There are roughly 42 years of nonstop sunlight at each pole, followed by 42 years of total darkness. The Sun faces Uranus’ equator during the time of the equinoxes, creating a period of day-night cycles resembling those on most other planets.
The near-polar areas of Uranus receive more energy from the Sun than its equatorial portions on average across the Uranian year as a result of this axis position. The equator of Uranus, however, is hotter than the poles. Unknown underlying factors are responsible for this. Although the cause of Uranus’ odd axial tilt is likewise unknown with certainty, the common theory holds that a protoplanet the size of Earth collided with Uranus during the formation of the Solar System, resulting in Uranus’s distorted orientation. According to research by Durham University’s Jacob Kegerreis, the planet’s tilt occurred between three and four billion years ago as a result of a planet-sized rock colliding with it.
When Voyager 2 flew by Uranus in 1986, its south pole was practically exactly facing the Sun. The International Astronomical Union now supports the definition that the north pole of a planet or satellite is the pole that points above the constant plane of the Solar System, regardless of the direction the planet is rotating. This definition is used to label this pole as “south.” In an alternative convention, the north and south poles of a body are occasionally determined using the right-hand rule in reference to the rotational axis.
Uranus’s apparent magnitude ranges between 5.38 and 6.03, with a mean of 5.68 and a standard deviation of 0.17. This brightness range is quite close to the threshold for human vision. The degree to which the planetary latitudes are lighted by the Sun and are visible from Earth determines a large portion of the variability. Its angular diameter is between 3.4 and 3.7 arcseconds, while Saturn’s is between 16 and 20 arcseconds and Jupiter’s is between 32 and 45 arcseconds. When Uranus is in opposition, it is visible to the unaided eye in dark sky and is a straightforward target for binoculars even in crowded cities.
At the time of Voyager 2’s flyby of Uranus in 1986, its south pole was nearly pointing directly at the Sun. Using the definition currently recognized by the International Astronomical Union, which states that the north pole of a planet or satellite is the pole that points above the constant plane of the Solar System, regardless of the direction the planet is rotating, this pole is designated as the “south.” An alternative convention is occasionally applied, where the north and south poles of a body are determined using the right-hand rule in reference to the rotational axis.
