As we march through the solar system, the seventh night of Chanukah brings us almost another billion miles further out, to the seventh planet from the sun, Uranus.
1) It takes Uranus 84 Earth years to finish a lap around the sun. That’s about the same as the average life expectancy of women living in 24 countries. The picture isn’t quite so optimistic for men, though.
2) While Earth is tilted about 23° relative to its orbital plane, Uranus’s tilt is almost 98°. So, it, its moons, and its rings all seem to roll around the solar system like a giant wheel or a rolling bullseye target. This tilt gives is some very strange seasons and day-night patterns. The equator gets direct sunlight during the time of the Uranian year near its equinoxes. Since the equator is facing the sun at these times, and a given point on the planet rotates toward and then away from the sun each day, this time of the year is the only time when there the rhythms of day and night are similar to the way they are on other planets. From equinox to equinox, the poles get 42 Earth years’-worth of continuous daylight, followed by 42 years of darkness.
3) Even though Uranus is as massive as 14 Earths, its gravity isn’t as strong as Earth’s. So, if you could find a place to stand, you’d weigh less there than you do on Earth.
4) Uranus’s rings were discovered in 1977, while astronomers were watching for it to occult a distant star. The star disappeared and reappeared five times before it disappeared behind the planet itself.
5) The only close-up view we’ve had of Uranus came in 1986, when Voyager 2 flew through its neighborhood. When it did, it discovered 10 moons, two more rings, and an almost completely featureless atmosphere. Voyager 1 could not be reached for comment. It’s recently been seen, though, that Uranus’s atmosphere isn’t boring, and there are storms and cloud bands that aren’t able to be seen in visible light.
6) Uranus has 27 moons, but compared to the other giant planets, Uranus’s are very small. It’s largest, Titania is less than half the size of the moon, and its five biggest moons, Titania, Miranda, Ariel, Unbriel, and Oberon are all less massive than Neptune’s moon, Triton.
7) Uranus is the coldest planet in the solar system, colder than the more distant Neptune. The lowest temperature measured there is 49 K; 49 degrees above absolute zero.
8) Uranus had been seen since ancient times, but since it moved so slowly compared the other starts nearby, people thought it was also a star. It was then discovered and rediscovered a few times before William Herschel discovered it again in 1781, and even that time it was kind of accidental. At first, he thought it was a comet, but before long he figured out it was a planet. Even after it was figured to be a planet, Herschel wanted to name it George’s Star (Georgium Sidus). The George in question was the king of England. This name didn’t fly outside England.