Geek Trivia: 21 years cold

What planet in our solar system has the harshest winter, one that is measured in decades?

What planet in our solar system has the harshest relative winter, one that is measured in decades?

Take a bow, Uranus, as your winter lasts roughly 21 Earth years. But that's not the half of it, as Uranus has the most extreme seasonal variation of any local planet.

Uranus' axial tilt is roughly 82 degrees, more than triple Earth's 23.5-degree inclination. In fact, it's really close to the 90-degree inclination (obviously) that would have its poles aligned with the ecliptic plane of the solar system.

Put another way, it's like someone knocked over Uranus, so that either its Southern or Northern hemisphere points away from the sun for half of Uranus' orbit. The wintering hemisphere is shrouded in almost persistent night, whilst the summer hemisphere bakes in almost perpetual sunlight. Thus, for one-quarter of its 84-Earth-year orbit, one of Uranus' poles endures the most extreme relative winter in our solar system.

Regardless of the season, Uranus is cold, with an average surface temperature (or, in the case of a gas giant, temperature at the tropopause) of -357 degrees Fahrenheit (-216 degrees Celsius).

Neptune actually has seasons that last over 42 Earth years, and its average surface temperature is slightly (four degrees Celsius) colder than that of Uranus, but Neptune experiences almost no appreciable seasonal changes in temperature or weather. It's equally cold all the time. The same is generally true of Venus, Jupiter, and Saturn -- they simply don't experience any major seasonal variation.

(As for Pluto, astronomers have no idea; it's not necessarily a planet, but its distance precludes any knowledge of whether it experiences seasons.)

Mars and Mercury, on the other hand, almost defy seasonal description. Mars has the most eccentric orbit of the local planets, with its distance from the sun changing so radically during the Martian year that Mars' atmospheric pressure swings by 25 percent, continent-sized dust storms rage across the planet, and the polar ice caps expand and contract visibly like mini-ice ages -- only with dry ice. Mercury, meanwhile, has a day that lasts 1.5 Mercurial years, no axial tilt, and no atmosphere to create weather, let alone seasons. However, Mercury's night is 1000 degrees Fahrenheit colder than its day -- except at the poles, where the temperature never changes.

That's not just calendar-crushing variation on a late spring, it's some seasonally sensational Geek Trivia.

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