Uranus is the seventh planet from the Sun, and it earns its “sideways” nickname because its rotation axis is tilted nearly 90 degrees from the plane of its orbit. Rather than spinning upright like a top, it rolls around the Sun on its side. NASA says a collision with an Earth-sized body long ago may have caused the tilt, but that explanation is a hypothesis, not an established certainty.
Why Uranus appears to roll around the Sun
Because the axis is almost parallel to the orbital plane, the planet’s poles take turns facing the Sun rather than its equator. NASA notes that one pole can point toward the Sun for nearly a quarter of the Uranian year. A single Uranian year lasts about 84 Earth years, so the result is seasons unlike any on the inner planets.
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What the seasons look like
- Long summer and winter: the pole tilted toward the Sun receives sunlight for a very long stretch of its orbit, while the opposite pole is turned away.
- Dark winter: NASA describes about 21 years of winter darkness for the hemisphere turned away from the Sun.
- Slow reversal: as the planet moves along its 84-year orbit, the sunlit pole gradually changes, so no season resembles an Earth season in length or pattern.
What is observed and what is still a hypothesis
Several features of Uranus are well documented, while others rest on interpretation. The table separates them so you can see which claims are direct observations and which are explanations or catalogue counts that may change.
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|---|---|---|
| Axial tilt of nearly 90 degrees | Observed | NASA Science, Uranus facts page (undated in the source consulted) |
| Tilt caused by a collision with an Earth-sized body | Hypothesis | NASA says this may explain the tilt; it is not established as certain |
| Magnetic axis tilted about 60 degrees from the spin axis and offset from the center | Observed during the 1986 flyby | NASA Science, Uranus facts page |
| Flyby magnetosphere readings affected by a solar-wind event | Reanalysis finding | NASA JPL report, November 11, 2024 |
| Voyager 2 as the only spacecraft to visit | Mission history | NASA mission pages and a 2025 NASA expert feature |
| 13 rings and 28 known moons | Catalogue count | NASA Science, Uranus facts page; counts can be updated as observations improve |
An ice giant with no surface to land on
Uranus belongs to the ice giant class, alongside Neptune. The word “ice” refers to chemistry, not to a frozen crust you could stand on. NASA says 80% or more of the planet’s mass is hot, dense fluid made of “icy” materials, namely water, methane, and ammonia, lying over a small rocky core. Because the interior grades into fluid, there is no true surface on which a lander could touch down.
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The outer atmosphere is mostly hydrogen and helium, with methane and traces of water and ammonia. Methane absorbs red light, so reflected sunlight leaves the planet looking blue-green.
Temperatures and winds
NASA’s facts page reports atmospheric temperatures as low as 49 K (-224.2 °C) and winds reaching 560 miles per hour (900 km/h). These are reference values published by NASA, not new measurements made for this article, so treat them as the figures NASA currently gives rather than fixed limits.
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A magnetic field that does not line up
NASA describes the magnetic axis as tilted nearly 60 degrees from the spin axis and offset from the planet’s center by about one-third of its radius. As a result, the field and the auroras it produces do not line up the way Earth’s do.
Voyager 2’s measurements during its 1986 flyby are a snapshot, and a November 11, 2024 NASA JPL report says reanalysis of the data indicates a solar-wind event was under way at the time. That event may help explain unusual magnetosphere readings, so the flyby should not be taken as typical of Uranus at all times.
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Rings and moons
NASA’s facts page lists 13 faint rings. As the page describes them, nine are narrow, dark inner rings, and two outer rings appear reddish and blue. The same page lists 28 known moons, whose names come from works by Shakespeare and Alexander Pope. Both counts reflect NASA’s current listing and could change as astronomers identify more objects.
Discovery, orbit, and day length
William Herschel discovered Uranus in 1781, the first planet found with the aid of a telescope. He initially thought it was a comet or a star. NASA describes its general acceptance as a planet about two years later, following observations that included those of Johann Elert Bode.
Uranus orbits the Sun at about 2.8 billion kilometers (1.7 billion miles), and one orbit takes about 84 years. Voyager 2 measured a day, meaning one rotation, as 17 hours and 14 minutes, according to NASA’s Voyager fact sheet.
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Yes, once. Voyager 2 flew past Uranus on January 24, 1986, and NASA says it is the only spacecraft to have visited. The close-range encounter lasted only hours. NASA’s 2025 expert feature and mission pages describe it that way, and no second close spacecraft visit appears in the NASA material consulted for this article. Nothing in that material indicates a human visit or landing, and none is possible with current technology for a planet with no surface to land on.
How Uranus compares with Neptune and Earth
Neptune: both planets are ice giants. According to NASA’s facts page, Uranus is slightly larger in diameter but less massive. The sources consulted do not support a broader ranking of weather, interior structure, or habitability between the two, so those comparisons are better left to dedicated studies.
Earth: the most useful axes are tilt, length of day and year, and surface. Earth’s axis is tilted far less than Uranus’s, Earth’s year is much shorter, and Earth has a solid surface, which Uranus lacks.
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